I am shocked that they did not configure the dust cover!  I think that their trigger and hammer are set a little further toward the front of the grip than what I did.   This may cause more conflicts than I encountered.  I kid you not, my dust cover works perfect and does not look like crap either! 

I would like to see yours (dust cover....LOL) when you get around to doing it, I did like the idea and would like to see it!  I would like to send BRP one of the ideas for the dust cover, as a matter of courtesy.  It is the least that could be done, since he showed the way for a semi MG42.  I am sure he tinkered with it but then again he was busy designing the rest of the thing, I dont even want to Monday morning QB him!

The dust cover mounts in 2 locations, one hole being the trunnion.  The other  hole is located right next to the grip stick on the charging handle side.  I just took a small die grinder bit (less than 1/8") and opened that hole away from the grip stick maybe 1/8". 

There was a small conflict where the grip was interfering with the rod that holds the dust cover.  This conflict was caused by the New Plates in the Grip Stick for the AR15 trigger Group.  Reaming this hole allowed clearance for both , now the rod lays right next to the grip stick which actually holds it tightly in place.  I will post pics in a day or two. 

I am very pleased with the project so far and everything works well in the dry fire simulation,  I just have to get access to a lathe and make that extension on the bolt.  The other part of the bolt is finished.

Any idea what they used for a firing pin?  If not I will make one on the lathe and talk to some one about hardening it or tempering it!  I would think it needs to be hardened the same way you would a "punch"......I am not sure maybe it dont even need to be hardened!

Here are some pictures of the BRP receiver.
 

Also the I.D. for the rails is the same as the FA.

Here are some pics of the Dust Cover modified.

1. 

2. 

3. 

A few more and note the bottom one shows the Dust Cover Rod slightly ajar with the grip stick removed....that is the hole that I elongated to allow the rod to nest right next to the grip stick when it is all seated! 

See 1st pic.

This pic 2,3 you can see the piece of steel that was welded to the spring loaded locking latch.  It was welded to the rear to still utilize the angle that is needed to allow the bolt charging handle catch to push it down and knock the latch catch and in turn open the dust cover. 

Not sure, but I seem to be missing something.  What's the reasoning behind moving grip into the ejector port?  Is this IAW the BRP/ATF authorization?

I thyink its to get the hammer lined up ( perpendicular ) to the firing pin.

there is not that much room to play with and that may have been a logical

way for them (BRP) to go.

 if you make the firing pin longer so you can move the

hammer trigger firing controls back into the grip, the firing pin

 will bottom out on the shock buff when the gun cycles

Removing or grinding away the steel in the Receiver where the FORWARD part of the Grip Stick would dock-up NEGATES the ability of using an original grip stick on the semi auto receiver that is being created!  The original Grip Stick has a Drop Down Sear which allows the OPEN Full Auto Bolt to cycle.  We are creating a closed bolt system that can not be restored back to FA.  It is a good idea to mount the new grip stick much differently than the original and to destroy the original way the original is mounted! 

If you must use a mig welder and/or other heavy milling machine shop type tools to make something illegal out of your project, you are not going to fall into the readily convertable or readily restorable back to Full Auto area.    

Moving the grip into the ejection port seems to solve these problems.  It would not be wise to cut corners in this department. 

IMO any of these projects that have even a hint of being readily restored may fall under the "once an mg always an mg BS". 

A parts kit that is welded up  into a dummy falls under these "once an mg......" rules. You see certain parts have not been removed, they actually get re-introduced on the dummies even though the dummy does not function.  That is why dummies with original parts are frowned upon by the ATF, they are not necessarily illegal but they could be upon inspection.  You are at the mercy of the inspectors judgement! 

We, on the other hand are taking a parts kit that has been destroyed by BATF standards and then permanently destroying its FA capability and manufacturing a new gun!  This is a very different story than the "dummy" project.  This is why it is very important to render the receiver impossibly restorable as an automatic weapon.

The dummy guns out there are not doing this, they are just welding barrels shut or putting lead in the breaches, or rendering the bolts useless then welding the receiver closed, or things of that nature!

IMO, again, I would recommend modifying your receivers to totally not allow the old grip stick by a very obvious means!

The MG42 is very simple, it has a Grip Stick that allows the bolt to go back and forth until the trigger is released.  The bolt cycles on a set of simple rails that guide it over the grip stick and into the breach, it is that simple!  Our only real choice to modify this and to control what the bolt does is to introduce the new grip stick and not allow the old one. 

BRP came up with this design and the BATF said OK.  I trust it and after studying it for some time it all makes perfect sense. 

Any one who does this project will learn as they go along and really understand the differences of how a closed bolt system works as opposed to the open bolt system the weapon originally had.  The guidelines of how the BATF defines a semi-automatic firearm are clearly noted in this design (BRP).  I have made sure that I have followed it very closely and even in some areas I have made extra sure I have complied with these guidlines. 

These are my opinions from spending countless hours on other forums and trying to learn how to do things in a legal manner.  I personally do not intend to walk on any thin lines either!  I may not be right on everything and would welcome all opinions....That is the whole point of posting on a forum.  This forum seems to be a bunch of us that have the same agenda and I want to help the guys who may lack in the engineering skills and hope the guys with the legal skills can help vice-versa.

On another note, does anyone have any ideas on finishing the gun.  I mean ie... painting, bluing, parkerizing...things of that nature.  I have instant gun bluing that blends real nice but it is far from looking great!  The pics of the BRP look as if it is painted with some hard enamel?????

Painting could cover up some of the inperfections rather nicely, what do you guys think?

If anyone needs parts I recommend this guy Robert Johnson.  He has all kind of stuff and his prices are great!

http://www.robertrtg.com/mg.html

Aren't we getting rails from Robert Johnson?????

I did get my rails from Robert Johnson, who is http://www.robertrtg.com/. They were MG3 rails which are actually better than original MG42 rails, they are made of harder steel.  The only thing is they do not have the holes drilled for the rivets.  I used my cut rails as a template to drill the holes in the new ones.  This procedure worked just fine.  I used nuts and bolts to hold the rails in place when I made my initial spot welds to put the receiver back together.  I also used clamps to make sure they were true to eacother as I welded them back up!  All worked out fine, there may be a better way but that is what I did! 

Question:

Does anyone have any idea what BRP did for the rear of the BOLT where the firing pin comes through?

It looks like to me that he possibly made a "bushing" that fits into the rear bolt body snugly inside the ejector part that strikes the buffer (you know the part that goes in and out of the rear of the bolt).  A hole is drilled in this bushing that allows the firing pin to travel through it. 

The "ejector" part is held in place by the BOLT GUIDE which coincidently goes through it and the bolt body from top to bottom.

I know that what I just said will not make sense to most but it was the best I can explain it.  There is a photo on the first page of this post that shows what I am talking about.  It is so nicely done that it looks factory original.  If you look at your bolt from your parts kit you will see exactly what I am talking about.

I had thought about just drilling through the "Bolt Guide" a hole big enough for the firing pin but......It looks like that part where the hole would be drilled (right dead center in the middle) is pretty thin.

Any ideas!...........How about you EZFEED?  I have looked over this forum and I see you got your @#*%  together!!!

Well, still haven't taken any pictures, but I have a report, of sorts, for you all.  The BRP gun is a mix of excellence and stupid shortcuts.  The receiver is a jewel.  The pin, 3/8 dia. is riveted in right behind the rear tripod lug.  Also the safety block in the pistol grip sticks up high enough to perform the same function.  Most of the other details have been covered here before.

   I fired about 45 rounds before the firing pin broke.  The way the bolt is set up, you must have a round in the chamber or the ejector "hammer" can go forward and leave the firing pin un-supported. There must be a spring inside the bolt to hold that plug in the back, out. The gun had severe "trigger snap" and there were fitting issues everywhere I turned. I am reluctant to be critical of Brian because I understand the enormous pressure he is under to manufacture the products he sells.  On the other hand, it would be less than truthfull to give the gun a totaly glowing report.  I think the fireing pin issue has been addressed here. 

   I spent four hours remaking the trigger group so it would function as intended.  I spent another four hours spring loading the ejector block in the back of the bolt so it would support the pin at all times, chambered round or not.  I did not have to change out any parts, just straighten out the parts so they would work.

If I have time, I'll figure out how to post some pictures later.  I'm not good at that.

larryr

Nothing gets done to the rails the mods are done to the receiver.

Receiver must be modified to:

NOT allow a stock grip stick

NOT allow a stock bolt to be used

FIRE from a CLOSED BOLT with a hammer and disconnector

An original grip stick and original bolt are used BUT are heavily modified.  These modifications interfere with certain mods that have been done to the receiver. 

i.e.    original bolt can not pass over the hammer in the modified grip stick (hammer is in the way).  Hammer sits more forward in the modified grip stick therefore metal must be ground away from receiver where it mounts in front.  A new catch must be added to the modified grip stick to allow it to grab receiver in a more forward position!   These are just to name a few!

All the info is on these pages of this post with detailed photos.  There is also a link to the homesmith section in herre somewhere also....good luck!

I may have missed this but does the BRP finally use the bolt catch?

There is different "lingo" used by some of us (no big deal!) what are you referring to as the bolt catch?

The internal piece that sits internally in the bolt or the piece on the bolt that sticks out for the charging handle to grab?

The BRP does not use the first thing I mentioned and the second is ground off the original and relocated to a different position to allow it to pass by the hammer when the bolt is cycled.

Although BRP does not use it another member here built his and incorporated it by drilling it hollow and allowing the firing pipn to ride in it.  I am working on a similar design myself.

Hope this answers your question!

larryr; the measurment from the rear of the reciever to the end of the thread at the muzzle is 37 11/16 according to the calibrated stanley tape. The distance from the pin at the rear of the pistol grip mount to the end of the thread at the muzzle is 33 9/16. the exact distance from the trunion to the muzzle does not need to exact as the booster asembly gives you a little to work with. I wish I could give you a moe exact measurement but I do not have anything to measure that long of a distance with any precision.

Thanks ScenarioL113. Yes I was refering to the internal spring device. I originally thought (like many others)it was speed reducer but it was being refered to as a bolt catch in this thread.

There was some discussion about its need and function in a semi auto design. I had originally thought of omiting that part and using a firing pin return spring in its place but MG81 scared me with the following two sentences:

"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."

Then there is the article at mg42.net which indicates it is used to correct a design flaw, although the flaw is only described as "prematurely unlocking due to harmonics in the roller/wedge system".

Before I build any conversion (with or without bolt catch) I would like to find a more detailed description of the problem. I'm still looking for a more detailed discussion of the problem. Haven't found any info.

art887, the bolt catch was intruduced after the 42 was intruduced into service becuse the guns were occasionally firing while the bolt was not fully locked into the barrel extension. This unlocking was caused by bolt bounce. The problem of bolt bounce is inherent in all full auto guns and most all semi auto guns. The bolt bounce problem can be explaned by what happens when you take a hammer and hit another metal object with it, the hammer bounces back, the same thing happens(on a much smaller scale) when the components of the bolt slam into the barrel extension. The bolt runs forward striking the barrel extension next the bolt carrier runs home pushing the locking wedge ahead of it the locking wedge carries the firing pin, the firing pin has just struck the primer igniting it,now the powder in the case is burning generating recoil and pressure while this is all going on the bolt carrier is in the proccess of bouncing back (think off the hammer) off the locking wedge and the bolt head this allows the locking rollers come out of battery  and the bolt can open even though the chamber pressure is still way too high. The spring in the bolt catch holds the locking wedge shut while the bolt carrier comes back to the fully forward and locked position from the bounce.I hope this helps. 
 

Thanks Mg81.

hehe... ok let me see if I got this yet.

The issue is bolt bounce - so in a semi design, their would only be an issue if you were to time your trigger pull as to have the hammer drop while the bolt is experiencing the bolt bounce (in other words near after chambering a round).

If you fire after chambering and the bolt is at rest ( bolt bounce has already occured), the bolt catch has no effect.

Is this right?
 

This bolt catch device.  I do understand its function but there has been some debate on it.  Nobody has really mentioned the spring,  is the spring necessary or is it more the weight of the item that helps the bolt bounce.

I planned on omitting the item but was thinking about turning one on the lathe as a solid piece and drilling it out hollow for the firing pin to go through it.  I figured this would work to support the firing pin, and help stabilize the bolt with the added weight.  It would also leave more options on locating the return spring to prevent slam firing......

I have not really decided what to do yet since there have been a few different ideas and opinions on the bolt and firing pin setup!  I could turn it on the lathe and incorporat the spring also but if it not necessary then it is a waste of time........I just want to prevent the broken firing pins.....any thoughts......

FV

senarioL113, the spring on the bolt catch is what does all the work, the weight of the bolt catch assembly is not the key to function. The catch assembly is simply a spring loaded plunger. Look at the ends of center part of the catch assembly you will see there are slots that the end pieces can move in on, it is that distance  that the spring can act on the locking wedge after the bolt carrier has moved to the rear.Put the assembeled bolt in the barrel extension and push it into battery and you will feel the action of the bolt catch spring as you push (very hard) in on the bolt carrier.  art887 the catch assy. is working every time the gun fires. in the full auto the firing sequence is startd by the bolt carrier running into the locked bolt. In a semi you no longer have that sequence of events, the firing sequence is started when the hammer hits the firing pin.The safegaurd of the bolt being closed and locked is no longer there. It is possible that the hammer can fall is the bolt carrier is not fully forward or is in the bounce proccess.The distance between locked and not locked  are so small that I don't think it's posssible to use the firing pin length the saftey mechanism for this problem, I think it would be to unreliable when you wanted it to fire.So the bolt catch is just as important in the semi as the full autos. One more thought the brp firing pins are breaking bucuse there is too much unsupperted area the bolt catch around the pin will eliminate that. I have never broken a pin in my gun , the issue with mine is riviting of the head where the hammer strikes it. I am working on a new design for the firing pin end. When I complete it I will post it,it will eliminate riviting and retention problems.(eta 4weeks or so) 

In talking to a few folks in-the-know, I really feel the best approch to me helping everyone is to build up a 80% MG42 receiver.  Here is what I feel should apply to keep all safe and legal.

1. The rewelded receiver needs to have the extra length cut thru the pistol grip opening so the stock grip cannot work.

2. The bolt rails will not be installed in the receiver.

3. A bar or side rail/bolt guide needs to be added to block the access of a unmodified MG42 bolt group.

I know that these steps are toward building the semi-auto, but I can't just reweld the receiver and ship it out without doing something else to prohibit the function of a live MG.  The only other way (which all here don't want to think about) is to build it up as a dummy receiver and add a friggin' welded piece of bar-stock down the middle of the receiver that you would never be able to cut out.  I will keep you all posted.  Thanks & signing off.

I will check around in the next few days to see if these items only will comply with ATF regs.

C2 and Big Mike,

Please see http://www.weaponeer.net/forum/forum_posts.asp?TID=376&PN=1

This is one of my letters stating the legality of building SA receivers from demilled receivers. The only stipulation in building a SA receiver from a controlled one is to ensure that the receiver was demilled to ATF specs BEFORE you reweld it. 

In receiver buildup, ATF wants there to be no "gray" areas during construction.  When rewelding the receiver on the 42 you need to start from the rear and weld in the block to prevent the FA bolt from installing. Once you finish the rear of the receiver to SA configuration you can then zap up the front. Know that anytime you reweld any demil cut you are violating the demil and from that point on you could be considered to be manufacturing a MG. Incorporate the SA mod FIRST when rewelding and your OK.   

C2, you should be OK in building 80% receivers with no problems legally and for sure the purchaser won't need to fill out a form 1 or any other form. You should be able to do the reweld in the legal fashion and return it to the customer at profit.  Just to cover your butt, find out what ATF will consider 80% on this FIRST. Sketch a drawing of what you want to do and write an explanatory letter and submit it to ATF fierearms tech branch. Be sure to state what it can and cannot accept!!!!!! The area forward of the trunnion you should be able to leave alone but the rear will have to have the mods.

All the semi conversions that I have had reclassified have been hampered by the exceptionally slow response time of ATFFTB. It seems that there must be a black hole that sucks up mail in between my house and their offices because I keep having things get lost on a regular basis. They're reall busy with all the Homeland Security stuff as well as the things they get from the PD's across the Nation so this is understandable. I'm told to fax things from now on because of this. ATFFTB just moved to a new office so their mail system should be better now and you should have less chance of them losing your letter but you can fax it to them as well to (304) 260-1701. (Their fax might be down right now but it will be up soon)

Never rely on word of mouth from ATF officials, many of the guys have different views on things and how they perceive your question and usually they will just try to get you off their back so they can finish their work. Many of them know the CFR's and different rulings back to front but for the most part they wont be able to give you a definite answer on anything but the simplest of questions over the phone. To cover themselves from persecution for giving you the wrong answer they choose the easiest way out and just tell you that whatever it is it's illegal (I think that's a smart move on their part). The only way for you to get a definite straight answer is if you submit it in writing. It's a wait but if you have it on paper it's concrete.

You don't really have to do the above but it is a measure to ensure that your butt is officially covered and the 80% is a legal, unregulated 80%. As long as the receiver is constructed to where it cannot accept the FA bolt, FA trigger housing, and cannot be finished in less than 8 hrs (I think that's the time span??) then you should be OK. For the most part you basically need to make a little less than a SA receiver.

Hope this helps!!!!!!!

Here are a few pictures of the milling process for opening the SA-42 trigger opening. This seems to be the most popular style everyone is wanting. Anyone here recognize their receiver? This was one of the earlier one done. More pics to follow later.

jeffcob; Sorry i have not replied to you but I just got my computer fixed after it decided to take a crap on me. I will measure the bolt extension and the shuttle for you and post the results. I do not have a scanner so I will have to put it all in text. As to the trimming of the driving spring, my gun uses the full length spring. I added an extension to the back of the buffer tube in the butstock to make up for the added length of the bolt extension.

Jeff. Cobb, thanks for the info on the feedtray, already milled out the spot and remounted using 8-32 fh screws instant conversion from 308 to 8mm with simple allen  heads. Being as work is getting slow and the tourists here in Wisconsin are as bad as mosquito's I do not spend much time fishing for muskies I might be able to help you guys that do not have a lathe and mill do some of those bolt conversions and extensions. I have to make mine yet I'll keep track of time but this would be a limited number being as I work full time 50-55hrs per week  I can do only so much. We get very short lead times on dies and form tools. Anybody with ideas let me know.

Well here she is, my camera isnt the best plus my lighing is bright.

I will post some pictures of the bolt and the little block I have inside the receiver to prevent the un-modified bolt installation when I take it apart to clean it (feeling kind of lazy right now ) after 1500 plus rounds I haven’t take the bolt out in a while its getting to be a pig pen in the receiver. But the bolt is an EXACT copy of BRP's in fact they will interchange and run (I have tried it, my semi42 bolt to brps and vice versa)

Notice how none of the weld shows thru the blue, it was blued with brownells number 7 formula after it was glass beaded then I ran the receiver thru brownells blue remover. I even blued the bolt carrier to match a blued original I had seen.

This is the style of Full Auto bolt stop I have made. Just a piece of steel radiused ends so the spring will not bind with a stud welded in  and to the reciever. The clearance on right side is for cocking nub on bolt which I made long and cut down the right side of grip frame to accomodate it. Their is close to a full 1/4" of engagement with the cocking arm so you can really pull on it.  It is probably overkill but I prefer it.

Thankyou Huntsinmtns, very nice pics! My trigger pac pin locations are probably off a little. I'll show it to a gun smith friend of mine to smoth it out. For the full auto bolt stopper I was just going to run a 7/16 l pop rivet up thru it. Or would that be to gray of an area with out welding it in place? Bolt is still at the machine shop, hope to get it back modified before Christmas . talk to ya latter Slowfinger

I would probably make a heavier type of stop, you can drill out a rivet very quickly. IMO the stronger the better that way no one could question it. Ask your machinist freind for a 3/8" x 1/2" dowel pin. It is hardend and very durable. Drill a 3/8" hole where you want and weld up the opposite side, make sure you put the bolt in 1st so you can get clearance for the extractor I used .040 between pin and extractor push down on bolt that way you know it will not bind, then weld.

The BRP 42 uses only a rivet. Installed in the back of the receiver. It actually goes thru the barrel reciprocator (and of course the receiver.) Why get carried away re-inventing the wheel save your time for the rest of the project you’ll need it.

I have a torch cut receiver that I'd like to build into a semi some day.But I heard that the receivers from BRP are saw cut.Is there any truth to this?Has anyone bought an MG42 parts kit from BRP?

The BRP receivers provided with their parts kits are useless, because they are saw cut they are missing large sections.

If you don't want to wait  for welding service....and can weld..... go back and rereed all the pages here on building a SA42 untill you fully under stand them and using your own kits parts as a jig and temp. install the rails with bolts for space and top cover. zap it up mig weld stlye. Have someone hold front piece in place with barrel installed. This needs to be close otherwise you may have to shorten your barrel a little bit like me. It turned out very ok and the basic ginding and sanding of welds in and outside. and you know what, I'm not a C2 person just a C&R. When doing the butstock piece fit every thing first. Then install buffer and or butstock assemble just to tack weld that area. Let cool and remove buffer and stock. You do this for two reasons, to get alingment for buffer assemble and spacing. Comeon guys this just is't hard to do. I wish I had time to do a few of them for you. But you can supprise yourself when the need arises. And it's FUN! 

Great advice Slowfinger!  By all legal rights, you just told guys here the steps to weld-up a illegal machine gun.  I hope you don't mention my name when ATF agents pay you a visit.  There are certain steps that need to be taken and in a certain order on these receivers BEFORE you even start welding or tack-welding ANYTHING.  I talked with BATF Tech Branch for several weeks before this all started, and they have no problem with going after who they can to arrest and prosecute on these kits.  They tried to shut it down with the confiscation and charges against Inter Ordnance on these MG kits.  Don't ruin it for these guys here (or anywhere).  Slowfinger, I really hope you were just joking, if not, go for it.  Just remember, when you drop your soap in the showers at the pen, don't bend over to pick it up!

salt6

Trunion disassembled.

The trunnion is in two parts (or should be, remove the rivet from the right side and slide the small rt. side section out), the large part will fit over the feed tray area and slide forward toward the muzzle. You'll need to use a rubber mallet (or similiar) to tap it forward into place. the small righthand part will theen slide into the grooves from the front of the barrel gate opening towards the rear. replace large rivet and your done.

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