Please post this for the other users who might have the same problem. I have been through the war, and looks like victory is at hand!

I ended up using both firing pins that came with my MG-42. The first one shot about 5 rounds, and then broke. Thinking this a fluke, I installed the second pin and got off about 15 rounds and the same thing happened. What puzzled me was that the pins were breaking on the rear side of the rear annular ferrule. A call to Brian at BRP cleared up the mystery. There's a hole in the end of the buffer (apparently where a screw went) that on some guns is pinching and grabbing the rear of the firing pin on recoil. The buffer is that piece of round shiny metal sticking forward of the butt stock. It's tearing the back end of the firing pin off. Brian says it isn't consistent with all of the production models since they had so many buffers to work with and they weren't absolutely consistent across the board. I talked with Brian on 2-2-04 and am sending him my buffer to be drilled out for firing pin clearance and he will replace the broken firing pins. He doesn't want any MG's out there that aren't working right. Hope that this helps.

Also, look at the post on 1919a4.com regarding a burr on the upper hammer sear of the BRP MG42. I had a burr on mine that I had to file slightly. How to find out:

1.      Remove trigger pack
2.      Let hammer fall forward gently (you gotta' restrain it by hand) to its "fired" rest position.
3.      Now, pull the trigger, and pull the hammer back fully (like the bolt affects it when it recoils)
4.      You will note that it is caught on the upper sear, even with the trigger pulled
5.      Remove your restraining hand from the hammer
6.      Let the trigger loose to move forward to its rest position
7.      The hammer should turn loose from the upper sear and catch on the lower sear.
8.      If the hammer doesn't release from the upper sear, nudge the trigger forward past the rest postion
9.      The hammer should then fall forward to catch on the lower sear

Now, if #8 happens, there's a burr on the upper sear that will be need to be removed with a couple of swipes of a file - DO NOT REMOVE MORE THAN ABSOLUTELY NECESSARY. After each swipe with a file, do 1-9 again until it works properly by skipping 8. Stop there. Friction and use will polish the job.
 

I think I finally understand the bolt pic. The extension in the rear of the bolt just moves the spring away from rear of the bolt and the slot is so the hammer can travel up through the slot to strike the firing pin. The spring must be shortened though??? Correct??? 

Another thing,

I see that the sear catch is milled into a little square. Is that for a disconnector? It would seem to me that it would be a good idea to weld a little bar or a flat rectangular plate on the rear floor of the receiver. The bolt can only be introduced through the rear of the receiver so this would prohibit a FA bolt from being inserted because the sear catch on the bolt would contact the plate. What did BRP do????

I was thinking of this problem with obtaining a letter. Let's just see if we can get some manuals as the manuals will have the company address and info on the gun. Can someone make some reprints??????

It MAY probably be a good idea to mark the receiver"Copy of BRP semi auto MG-42"

Anyone should be able to build one of these. Even if you're a crappy welder you can still reweld this receiver because the receiver itself takes no load from the cartridge. The barrel collar takes the load when locked to the bolt.

 I think the disconector is in the trigger pack ar style and the little squqar is actuly welded on the bolt body to facillitate the cocking slide bar and a bar welded to the bottom of the reciver will interfeer with its operation

not to burst your bubble but welding that reciver will be no walk in the park. x and y axiel plane plus aradial one to boot . welding two pices togather is not to bad but five is a bit more difficult .

there is not realy a building line to work off of except that of the bore

this will take some thinking

You are correct with you observation on the bolt extension.

That is not a sear catch at all, that is the new cocking nub for the charging handle. If it were centered across the pad like it was originally it would hit the silver block in the grip stick, this piece prevents the FA bolt from being installed.

I have studied the pictures an e-mail back in forth with the owner of this BRP gun, he seems to think that the rails were moved in just a hair, but I don’t believe so since the width of the bolt appears untouched. Since he doesn’t own a FA bolt I sent him some measurement off some of mine. To confirm this rumor.

With a nice thick flat (metal) work surface and good tig welding the receiver is a walk in the park!!
 

screwed up I forgot about the charging handle!!!!!!!!!!

Actually welding this thing back up will be a walk in the park for me!!! The hardest receiver I have ever had to reweld is the one for a DShK and that was due to it being almost 1/2" thick in some places.

To start rewelding you must first have a good level surface to start with and ensure that the receiver components are nice and square and not warped from demill. This is actually not too much a problem because their demil guys are good. Another thing is that you canot use a rewelding jig like the ones I have designed for the Bren and DShK. You will have to use small pieces of copper for backups. You will have to clamp the sections to the work surface (on top of a copper plate) and work one cut at a time. Be sure to start from the rear and incorporate your semi route into the first weld as once you start to reweld just one cut you have violated demill.

From the booster cone to the trunnion is original 42 on a BRP so this is why I stress this to you guys. Working on the shroud first will constitute construction of an MG because it is considered part of the receiver by ATF. As you weld this thing back up be carefull of warpage and use heat sinks. Once you have secured one component down to the work surface use a straight edge to line up the next section. Take note of the position of the forward section of demilled rails in the rec. and mirror them to the the new ones to give you the correct measurement.

Be carefull and stay legal!!!!!!!!!!!!!!

Just a note:

I spoke to Brian at BRP Guns and asked to purchase an MG42 semi-auto bolt.  He replied after a week or so and told me NO PROBLEM!  He said that he has a limited supply of bolts and parts right now but they would be available at a later time!  I then asked if I supplied the bolt could he do it, again he replied and said yes.  If I sent him my bolt he would do it for $250.00.  Remember you must supply the bolt!

$250.00 to me is a very fair price!  There is a lot of fabrication involved and if you screw up you can ruin the bolt and will have to start from scratch. 

I am not going to purchase one at this time but I did want to share the info with the forum!

The MG42 Semi-Auto bolt is the heart of the semi conversion and can only be done with a mig welder and a lathe to fabricate the extension and the dimple recess to allow the spring to seat in the rear of the bolt!

The pistol assembly is a little chore but can be done in the basement as well as the rest of the project!

If any one attempts the project remember to modify where the pistol mounts to the receiver as a priority!  The original pistol assembly must not be able to be mounted in the semi-auto and modifying the receiver to not accept one is a big step in avoiding the accidental fabrication of what the BATF may interperate as a machinegun!  Having a spare STRIPPED Full Auto pistol grip on hand would be a good idea to show if it was ever questioned.  This would cover your ass in the "intent" dept!

This is a do-able project by anyone who considers himself a hobbyist!  It may not be as pretty as BRP's but I am sure it is possible.   A Lathe, Drill Press, MIG Welder, Bench Grinder/Wire Wheel,  Die Grinder/Dremmel, should be all you need...maybe a Mill but not necessary.  You can get a mini lathe for $300.00 bucks (Harbor Freight Tools).  It may come in handy to fabricate the firing pin also but I am not positive of that!

Good luck and if any questions let me know I have put forth a lot of thought into doing this project and would be glad to share any info with anyone interested!  I will do this!

I was told by others that Brian at BRP is a good guy and I am sure that he knows that his design will be copied by others.  As long as no one is selling his design there should be no problem!  It is perfectly legal to build your own rifle and that is all this is!  I do stress that the receiver must not accept an original grip stick.  The new grip stick must be modified to no longer accept the drop down sear.  Cutting the area out and then welding plates on it with the pin holes for the AR15 trigger and hammer does accomplish this! 

Remember this is a home build and copying the design not for resale is legal.  I personally would not condone any Class 2 copying this and selling them because that is illegal and morally wrong!

I have 90% completed the Grip assembly and it works well.  It is not an exact copy, I actually did it slightly different and am currently working on the "safety" which I will complete in the next few days but the rest works fine.  Trigger, disconnector, and the hammer.  The disconnector has to be "smithed" a little bit to catch the sear when released.  The hammer must be "smithed" alot to allow it to fall deep enough for the bolt to pass over rearward and FORWARD!

I only have the section completed where the grip stick mounts and sliding  the bolt on the rails just on this section.  Once I feel it is good I will weld the next pieces of the receiver together.  Once I get the safety done this will no longer accept Full Auto bolt or sear parts and it will be OK to complete.  The stock bolt sear catch cannot pass over the hammer there is not enough clearance that is why the new bolt has the catch to the side where it cears the hammer by about 1/8".   This will not allow FA parts therefore it is OK to continue!

Here are the SA bolt specs, I havent had a chance yet to compare them to the FA bolt yet. These measurements were taken with a certified set of calipers.

1. 1.092 Front of Bolt Body to Front of Charging Handle Lug
2. .500& Lug depth front to back
3. .150& Lug thickness
4. 1.150& Top of Bolt Body to bottom of Lug

5. 2.960& - Bolt Extension length (new extension where welded to orig. Bolt Body)
6. 1.270& Extension diameter
7. .990 Extension top flat to extension bottom flat
8. .625& Extension Guide width measured from top guide to underside of bottom Guide
9. .625& Extension Guide length (measured from front to rear)
10. 1.192& Extension rear counterbore dia
11. .184&Extension rear counterbore depth

OK here is what I am going to do and I think this is what BRP did as well. Either way it WILL work.

Take your bolt apart and find part #99,,,,,,chunk it. You cant use it from what I see. Also part #68 from what I see is not like what we have. Our rotator (feed arm stud, whatever you call it) is a solid part that is staked into the bolt body but is still loose to allow it to rotate. As eveyone knows other guns like the 1919 don't have such fancy things like this, the 1919's is just a fixed stud and quite smaller than this so I would say that keeping it to where it rotates is unneccessary.

On the bottom of the bolt body I would take a cutoff wheel and make a slice accross the surface intercepting both bolt in a permanent location (no more rotation). Carefully drill a hole through it's center for the firing pin to slide through. Now you could also possibly drill it out larger but you will have to open up the slots on the ejector extension as well. This may give you more meat to play with for the hole but you probably don't need it.

Drill through part #67 using the FP hole as a guide. Now you will reassemble your bolt without #99 and set the bolt in the locked position and insert a straight wire or peice of clotheshanger through the rear of the bolt all the way out through the firing pin hole. Note how far it protrudes (try to make it protrude out as far as the original in fire position) and hold it there and mark it on the rod on the rear side (ejector side). This will give you the roundabout length of your new firing pin. Give yourself 1/16"-1/8" to play with.

I think the FP that BRP made is ridiculous, it seems to thin. You should be able to turn one out of 1/4" stock or so with two stepped down areas. One step down area will be long and that will be the cartridge side. The other side wont be very long, maybe 1/2" or so. This short end will be the end inserted into the bolt body and will pass through the hole you put in the feed arm stud and the 1/4" area will back up on it and allow only 1/4" or so of the smaller diameter to protrude from the rear.  The long side will be protruding from the bolt head side and you will slip you ejector in and FP spring will slide over as well and back up between the larger diameter FP body and the flat side of #67. Now assemble the bolt and you will have a spring loaded FP that can be pushed forward from the rear and will retract on it's own (when bolt is locked).

Now I bet you're wondering what will happen when the bolt recoils with the pin protruding a bit from the rear and a empty case in the mouth of the bolt.  Bet you're worried that as the buffer enters the welded on spacer shroud and impacts the ejector it will break or otherwise hammer out the end of the firing pin (side that the hammer strikes). Here's the answer.

Look into the buffer (in the middle of the spring) and you will see a flat headed screw. You will drill small pocket into the head of this screw so that the end of the FP will have a recess to go into to escape damage when the buffer impacts the ejector.

Hope this helps!!!!!!! I'm just doing this in my mind but I will get around to it eventually!!!!!!!!!!

I dont know what brp used, but until I get access to a lathe my fp is a lenth of 1/8 309 welding rod w/ 2 washers welded in place . I started with an ar15 fp welded to a larger dia stock . but the gun ran away !! There is compomise in there, weight / spring compresseion/ hammer speed ect. test it with a short belt and watch your primers as there is no #99 in the bolt to  keep it locked up until the pressure drops.

Just my 2 ct's worth

When your bolt was locked was the FP  COMPLETLEY  withdrawn? If yes then I would look at your spring. When the bolt locks up into it's collar it is a pretty abrupt thing. You may have too much front to rear movement and because the FP is pretty heavy, it may be slamming forward upon chambering a round.

This is a good place to start checking. You may need a stiffer spring.

Also your FP may be too long. It doesn't have to be flush with the bolt face when retracted. It can be a little way in there but not much. I am working from a drawing I made right now and I see alot of play in there.

I'll drink to that!!

I figured the part about drilling through the "Feed Arm Stud" but I was not sure how to incorporate a spring to keep the FP retracted.

It made better sense when I drew it on paper as I read your post.

Great idea for figuring length also! 

Can not get over to buddies place to use his lathe, so I just bought one!  Once it comes in I can do the bolt extension and the lathe right here at the house! 

Then hopefully my fingers will be sore from loading empty belts by hand!

By the way, EZFEED you are a bad influence.......After reading some of your posts I probably will have a neverending supply of semi-builds that are waiting to be done in my basement!  But I will have a crapload fun guns to shoot!

Just imagine Smithys pin but turned out of a peice of 1/4" round stock (1/4" or whatever would fit best). The spring would back up between the flat round side of #67 and, looking at Smithys pin again, the large welded on centralizer on the cartridge side of the pin (left side of the pic).

Tension from the spring pushing against these two areas which are closer together when the bolt is locked, forces the pin back towards the rear of the bolt butting it up against feed arm stud. This also forces the pin to protrude from the rear of the bolt for the hamer to strike it. What keeps the pin from being pushed out the rear of the bolt is the rear centralizer (right side of pic) butting up against the now stationary and drilled through feed arm stud.

You ought to visit and join:

http://www.1919a4.com/ (kind of everyones home here!!!! the Mother site!!)

http://www.brenlmg.com/

http://www.m2hb.net/

www.m2hb.net/dshk/index.php (my specialty!!!!!!!!)

This stuffs just too fun!!!!!!!!!! I wish ATF would see it like we see it!!!!!

The Firing Pin looks much like a standard M60 firing pin
 

I think the M60 Firing Pin closely resembles BRP's but I think it is too short.  I think the M60 used 2 different Pins over the years and the longest was just under 5 inches.....4.97 or close to it!  It may be utilized if an extension is put on it.  I think one of us with a lathe could make some up for everyone interested.....I am sure we all could work something out.....to cover costs.   I do not think they will cost much at all to make them up... stock is very inexpensive, the only trick is to heat treat and temper it! (which I do not know how to do!)
 

The M60 firing pin uses an extension on the end. The only thing I don't like about the M60 firing pin is it's not chrome plated like the M16. I'm sure the bolt would require a lot of modifications, but using a standard firign pin has advantaged when you need to replace one!

Then again it may be more work than it's worth.

What about using two AR pins but don't weld them together.  The aft pin would be trimmed to fit the overall desire length.  Might use a cotter pin for each to hold it in a sleeved and extended bolt.  Additionally each pin could have it's own light-weight spring to keep FP inertia low enough to prevent a runaway.

We are all trying to come up with a functioning idea and sometimes the end result is "Whatever works!".  I like one continuos pin, with one piece there are no tolerences to deal with and no extra wear points.   The 2 piece MG42 bolt is a little sloppy to begin with (well mine is) and when the rollers lock it moves forward to allow the triangular FP holder to go forward (more play), I feel a continous FP may work better!

If someone comes up with a 2 piece

Hey guys, I met with Brian at BRP yesterday to check on some items he has of mine. In talking with him I asked about him doing Bolt and trigger work for those of us that purchased 42 kits. He said that he would do the work on our parts or as trade in parts towards the purchase of his trigger groups and bolts. Most of his kits are matching numbers so he doesn't want to sell out parts.

He also said he doesn't mind people using his design either and thought it was kind of cool. As for the receivers, which cost him a bunch of money to get set up and stamped he indicated for his design to work best, you really needed one of his. (this is not meant to deter the home welder). I saw many of them after the black oxide finish was applied, and it was very nicely done and looked great.

He has a finite amount of kits and doesn't have "spares" to sell, but would be interested in reworking our parts for a fee. What the fee is, I didn't get into. I would be happy to coordinate with Brian if there is interest in several people having their parts milled and reworked to the BRP design. Keep in mind that the original receiver would have to be modified to the BRP design. He would also sell receivers as well in the white.

The information shared on this site is excellent and I don't want to take away from any of the designs and ideas noted in the forum. All are very impressive. However for some of the less machined inclined, having BRP mill the weld and modify our parts might save an eye or two when we try out our basement products at the range.

Drop me an email if you are interested.

Conical One

I built a semi 42 two years ago . BRP did exactly what I did with the AR internalsin the trigger pack. The bolt catch(#99)should be retained at all costs. It is n easy matter to turn a tube to replace the solid center section of the bolt catch through that the firing pin can pass. My firing pin is a piece of 1/8" drill rod with a collar soldered on to it . The collar sits between the post of the feed stud( now soldered in place) and the rear of the hollow bolt catch. No firing pin spring is required. My gun has never slam fired.The imoprtance of the bolt catch is obvious when you think of how the mg42 locks up. The germans exerienced blow up untill this part was introduced. I would like to keep my eyesight and skin.

MG81

I had thought of drilling through this piece (#99) but kind of got presuaded against it when I saw BRP successfully omitted it!

I did not logically figure out how to either drill through it or replace a part with a hollow tube. 

Do you think you could post a schematic drawing of this or explain it in intricate detail?

I would definately try to employ the idea?

FV

the bolt catch is inerta activated how can it work staticly ? re firing from a closed bolt

The bolt catch forces the locking wedge to hold the rollers locked for a millisecond or so by compressing as the inertia of the bolt head is trying to force the rollers in (the locking wedge back). As the rear of the bolt body  starts to move to the rear the spring on the bolt catch extends and lets the locking wedge move to the rear and then the rollers can unlock from the barrel extension. The tube I made for catch is the same dimension as the original except it now has a hole for the firing pin to pass through. It can be made by duplicating the diameter of the original and then boring the hole and then mount it in a mill and mill the flats for the retaining pins to slide in (4 of them). After this is done you must relieve the interior of the bolt carrier as the bolt catch is now on the centerline of the carrier. In the original form it is not .You must remove this material to provide room for the ejector activator to work. 

Oops I forgot, most all of the kits come with the 750 gram bolt(weight) if your are lucky enough to have gotten a 950 bolt the catch was never installed in the they used a solid "inertia piece" and you do not need the spring loaded piece as the extra mass of the carrier provides the same function as the spring on the bolt catch.

maby i'm missing somthing but the bolt catch is to short to (it rattles) keep constant pressure on the firing pin holder ?

I must also be missing something cause I dont understand how the bolt catch can work statically.
 

In a semi design, I *assumed* that when the hammer struck the firing pin, it and the spring between the firing pin and bolt body would assist in pushing the bolt forward to help lock it if needed. The hammer/spring would be applying some force to help delay premature unlocking of the bolt also, possibly preventing a "nasty".
Ofcourse I may not know what the heck I am talking about too

OK me too, I do not see where this part is neccessary for SA. We will not be running at 1500 RPM so I can see no use for it. Evidentally BRP feels the same.

And to add another thing,

The trunnion cams are responsible for actuating the unlocking and locking of the rollers assisted with force from the drive spring.

I am however experiencing this fkcunig problem when i first started my testing i was using a heavy fp and experiencing run on then I went the lighter for mentioned fp ok sfsg with the exception of primer craters on all cases re cold barrel, hot barrel ,CZ ammo,AUS ammo,US ammo all w/same thing.

 then holes in the primers tried different ammo CZ ammo,AUS ammo,US ammo all w/same thing.  any one know how to check head-space on a 42 not theories but factory tolerances. My main spring has 5 coils cut off I couldn't fit one more the receiver is 1/6 " shorter than specs trunnion fit up is good. recupper? booster cone is proper size. I just don't know

the funny thing is when it had run on it was flawless ( the spent cases that is)

Let me try a different angle. The catch #12 is not loose in the bolt  when the bolt is locked into battery, you can put the complete bolt into the barrel extension and when the rollers are locked you will feel spring tension on the bolt carrier when you try to push in on it. This spring tension keeps the locking wedge#8 locked even though the bolt carrier has started to move to the rear as the round fires. It is correct that it is the job of the trunion cams to unlock the rollers BUT the important part is that the bolt catch DELAYS the unlocking of the rollers. As the round in the chamber fires the recoil force moves the barrel and bolt head to the rear, the  bolt carrier being a seperate part is also moved but as the bolt head (for lack of a better term) smackes the bolt carrier and starts to move it to the rear the spring on the bolt catch since it was compressed as all this started starts to expand but becuse the bolt carrier weighs less than the barrel and bolt head it must push the bolt carrier to the rear AS the assembly is recoiling BEFORE the locking wedge can allow the rollers to unlock.With out the bolt catch as soon as the assembly starts to the rear there would be no delay in the roller unlocking. Becuse as soon as the trunion cams act on the l;ocking rollers and push in the wedge#8 is more or less "squirted" out from the pressure on the rollers. And the fact that these guns are no longer full auto 1500 to 1800 rounds a minute has no bearing on this firing cycle. In full auto form the gun will not fire unless locked up becuse the firing pin is fixed in the wedge#8, but now it will fire as soon as the hammer hits the firing pin regardless if the rollers are locked or not. if the firing pin length is off even a very little the hammer will hit the firing pin before the bolt all the way forward. I know this has been very long winded but I hope this explanation helps.( Think Benelli shotgun it's the same principle of operation) The bolt catch DELAYS unlocking that is the key to understanding it's function. The germans introduced it to control bolt bounce but we need it for safety.

Should have read the board first, but in responce to "smithy" my gun has the full length main spring. I made a tube extension the same length as the bolt carrier extension and welded this tube to the back of the buffer tube inside the buttstock. By doing this you can keep the full spring length and operating travel of the bolt.

I used the BROWNELLS Aluma Hyde in semi-black to paint my Semi-receiver.  The Brownell stuff works great and dries real hard.  I will post a few pics when I get the Gun back together.

Still waiting to finish the bolt extension and firing pin..........I can not wait to fire this thing!

FV

OK,

Not to beat a dead horse but here is a pic from the inside of the receiver.  It shows the Dust Cover in its final form.

Note:

a. The silver block just to the right of the hammer is the dual purpose forward mount of the grip stick.  It has a lip toward the front (which catches the Dust Cover Latch) and a lip toward the rear (which catches the receiver).  

There are other ways probably but this works for me.

b. The  piece in the middle (that looks like it should not be there) gets tripped by  the Bolt Catch to open it up when you cycle the bolt to load up a belt.

This was posted earlier but since it was finished I think it is easier to make out without all the grinding marks and scratches!

The flash reflection is hard to eliminate but here it is:

So the spring on the bolt catch acts as the fp return spring?

That bolt Catch #99 assembly:

Is that the original one that has been drilled through to allow the firing pin to travel through it?

OR

Is it a new one that you turned on a lathe? If so how did you do it and keep the spring?  Does it come apart?

FV

The center of the bolt catch is a new part. It is easy to make, bore a .130 hole in a piece of bar stock then mount this between centers and turn the outside to the same diameter as the original center section of the bolt catch, cut to length, then mill the four flats to take the retaining pins of the end caps. A sleeve is then turned to press over the rear end of the rear cap and the open section of this is opened up to clear the collar on the firing pin. My firing pin has no return spring and does not need one. the drag from the floating bolt catch is enough to prevent slam fires. My gun has never slam fired or failed to fire when the trigger is pulled. The bolt catch in no way affects the return of the firing pin, the pin floats in the bolt.My bolt catch assembly comes apart the same way as the original by removing the four pins.

mg81

I can not figure out how to get the thing apart!

Does the spring need to be compressed to get to the 4 pins? If it is it very hard to compress!

I am confused on how to do this, usually I figure these thing out but I am stuck on this one...

To dissassemble the bolt catch the spring does not need to be compressed, but the spring is quite strong. If you closley examine the four retaining pins you will see that one end of the pins looks bigger than the other this is from the splines pressed on the pins opening up the holes they sit in as they are pressed in. To remove the pins you will need a short starter punch that fits well. Find the small end of the pin and with the bolt catch in a bench block give the starter pinch a GOOD smack with the hammer and the pin will move, drift it out the rest of the way with a regular punch. When you remove the other pin on the same end of the catch assembly be sure you contain the components as the spring and the rest of the bolt catch assembly will become airborne when the last pin moves out if you don't.

I must have a different type of Bolt Catch.  Mine does not have pins that are accessible, there is only one hole in each of the end caps.  Weird, it must be either an early or late version, on Robert Johnsons site there are 2 slightly different versions of this device.

Enough said, I sawzalled the freakin thing in half (it is being replaced anyway!).  As I thought there is no retaining pins on mine, there is actually a retaining washer (snap ring type of item) of some sort that is actually in therer that holds the thing together.  The end caps cannot come off!

I would have to think that this is not a servicabe item.

I know this sounds wierd but I messed with this stupid thing for a few hours to no avail!

No problem because I will fabricate an entire new one on the Lathe!  With pins!!!

I do want to incorporate this item whether it is needed or not because it holds the firing pin so nicely in its place and will support it pretty much the entire length!

The Bolt catch will not center or hold the firing pin in the bolt carrier, it's the other way around, the firing pin centers the bolt catch. If you make a new one you could incease the diameter.  In the stock form the bolt catch is smaller in diameter than the bore in the bolt carrier becuse the ejector activator must ride above it inside the bolt carrier.When I made mine I milled and ground out the inside of the bolt carrier so there would be room for the ejector activator above the bolt catch that is now centered inside the bolt carrier. I have never seen a different style of catch assembly, sorry if I led you on a wrong turn.

So is this component only needed on the lighter bolt????

I was thinking I could add some weight and forgo machining of this peice. Surely the new skirt welded to the bolt bumps up the weight to what is needed.

No problem like I said I will manufacture a whole new assembly, it is really no big deal.

Here is a pic of the different one:

They may have kept the different types of catches secured with different types of pins or snap ring type devices.  If you have a lathe it is really easy to just turn all the parts you need from stock and drill holes yourself to add the pins. 

FROM TOP TO BOTTOM
1. Yugo straight jacket, holds the the bolt wedge under pressure throughout the firing cycle
2.-3. Only apply presure to the bolt locking wedge when counter-bouncing against it.
4. MG3 bolt catch , which works the same as #2\3 , but is shorter and designed to bounce back and forth inside the bolt carrier, hammering the bolt locking wedge to keep it forward until the camming piece unlocks the bolt/barrel connection.

Nice to see a picture of the different style bolt catches. As to the bolt catch not being used in the 950 gram bolt, the heavy bolt uses a solid bar called an inertia piece that does the same job as the spring loaded part. The 950 gram bolt is quite a bit larger, I don't think it would be feasable th weld enough material on the 750 gram bolt to get it to this weight. The 950 bolt is a large rectangular shape that extends into the guide rails the full length of the bolt carrier and is very thick in sross section. I have put some thought into the prospect of making the rear of a new bolt carrier in this style and then welding the lugs and short section of tube from the original 750 gram carrier. I don't think this would be to difficult to do but I just have not got around to it yet.

Regarding the bolt conversion involving a bolt catch:

I am in the process of combining all the emails that have been posted here on this subject.  This should explain why this conversion is superior to the BRP method.

If I can get dimensions on the various parts, I have friend who has volunteered to do AutoCad drawings for us.  She (yes, a woman) is excited about doing this and would like to include all information that can be given to her.

When finished, the narrative, photos, AutoCad drawings, etc., would be available to anybody that contributed to this effort of designing a better bolt conversion as well as every friend of these contributors.

Hopefully someone can be found to convert bolts for those of us who do not have the expertise/facilities to do so - much like c2builder is doing on the receivers.  Obviously there is a market for SA-42's (as c2builder has called this rifle) as evidenced by BRP, TNW (who has advertised their waiting list on the website) and perhaps even US Ordnance (where I spoke to Curtis a while back about the semi project and got on their mailing list) and therefore there must be a market for the converted components for the homebuilt world.

Till later,

jeffcobb

Jeff

I am working on gathering all the details for everyone along pictures of the completed 42 and some of the rivet tooling used (this was the biggest pain in the a-s)
-I have spoken with my tig welder buddy to find out exactly what rod\wire we used.
-Also will confirm the brownells formula my gunsmith used (I believe its #7)
- I was fortunate enough to borrow a BRP from a friend to copy it exactly.

After studying BRP’s 42 One very important piece was omitted which I believe makes for a much better performing semi. Due to the increased SA bolt length when charging it is so critical to pull the bolt all the way till it contacts the buffer. The reason is simple; it needs ALL the power of the compressed (now shortened) recoil spring to always have enough force to push the cartridge out of the belt.
What I noticed about brp’s 42 is most shooters will pull the bolt back to charge the round and aren’t able to keep the bolt all the way on the buffer and quickly remove their hand from the cocking handle. What happens is the operator just for a split second will surf the cocking handle, this drastically reduces the amount of energy the new bolt will need to effectively strip and chamber the round EVERY time. Also they are the biggest pain in the but to change the barrel because there is no way to lock the bolt back!!!!!!

So what I incorporated into my design is an opposing wedge to hold the bolt back. This is located right in front of the factory stop, this result is awesome and snaps shut like two dozen mouse traps which insures it will strip and chamber the round every time.


More to come…

Dear ak47dennis,

Thank you so very much for sharing.

So the defect with the BRP bolt conversion maybe insuffient forward spring thrust on initial charging stroke.  A bolt hold open device overcomes this problem.  I think we will all find a hold open capability a much enjoyed for the  SA-42.

I take it, you have had no problem with broken firing pins.

Very interesting.  Again we all look forward to your future comments about your success.

Till later,

jeffcobb

Hey Dennis,

Do you think it would help if we reduced the amount of spring that was shortened? (I'm talking about when you trim the drive spring for the skirt) If we left maybe a coil or two more extra maybe it would help out a little? Is there not enough clearance? It would seem that with the increase bolt weight, it would have enough umph to strip the cartridges with ease?

EZ

What I discovered is if you leave the re-coil spring as much as a 1/2 coil to long your 42 will not eject. The spring needs to really be installed and tested to get the length just perfect. If it’s a tad to long the spring will "stack" and the bolt wont contact the buffer = no ejection. If you remove too much from the length it will lack power to strip the rounds from the later war dated belts.
The later (war dated) belts have the little dimples to increase the tension on the cartridge. The earlier belts are smooth and I believe made from spring steel material.

Also the "newer" style BRP firing pins have the edges radiuses which seem to have eliminated breakage.

anybody set up to drill through the hardened steel striker for the original firing pin?

 i gave it a shot and real quick saw i was getting nowhere, then tried two local machine-shops to see if they'd be able to anneal ,drill , and re-harden,  but their not interested in such small work and winded up giving me the run around until it became obvious they didn't want the job.   

Yeah, that can be done w/out annealing and rehardening it. Can do the back of bolt carrier for your feed stud also. E-mail me

Some of guys have asked for extensions only, not a problem 35.00 includes shipping. Let me know what you need.

Drooling Idiot,  

 You need a drill press and a  CARBIDE Drill bit to get thru the hardened steel.  I think a 2 flute carbide bit to be more specific.  This was discussed very early on in this thread and if you look there may actually be a link to a place where you can buy one.
I also did not even scratch it when I tried at fiirst.  After I got the carbide drill bit it went thru fairly easily, just go slow and it will steadily go thru.
Since it is  now hollow, the urgency of being hardened is not  a problem anymore.
I am sure others will agree. 

Today while reworking some post war bolts I ran into a new problem. These bolts have the ejector collar hole offset. This is the piece that contacts the buffer, when your FP is thru the hole and your retainer comes in contact with it will wipe it out real fast. This is on 2 post war steyr bolts that I recieved. Just so you guys know.

If any one has rails not installed yet , could you please measure and tell me the length of them?    Thanks

Looks to be around 13 3/16" with tape measure, If you need a more accurate reading I can use large calipers at work.

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