Receivers from BRP

[Der Alder]

That looks really nice.

[Abominog]

Bravo!

We've lost so many photos over the years- you guys keep up the photo study and discussion to rebuild the lessons!

[Der Alder]

Bravo!

We've lost so many photos over the years- you guys keep up the photo study and discussion to rebuild the lessons!

That's what I'm thinking. Lets use Rodom's build to do an updated semi build. We have had some fantastic tutorial builds here over the years, Pirate, Oak, Flem, Road Runner, the list goes on. I'll throw some of my own pics in from past and current builds as well. There have been a lot of new parts from RTG, BRP and Global Machining that have became available since many of these tutorials were made a few years ago, so perhaps its time for an update anyway. That and I'd like to show that this can be done with hands tools in your garage if you are persistent.

So now that we have the front done, lets move to the next step. We need to get the shells welded together.

[Der Alder]

But first;
Remember the theme of this build is "short cut/garage build", as in using the super easy to install MG3 front bushing all the way back to the MG3 rear receiver stub (no riveting). That and this build will be done with hand tools, no mill needed. I am in no way saying this is the best way to do any of this (its not by any means), but its a way many garage builders could make one of these guns in their spare time with minimum tools using the tools most will have on hand.

Tools; as in a wire welder, dremel (and a few jumbo pacs of fiber cut-off wheels), a drill press can be nice but not necessary, A belt sander, even a small hand held type will be very helpful, some good metal working hand files too. A small carpenters square,a level, a good 3' long straight edge ruler, a tape measure in both inch and metric and your most important tool of all - a good dial caliper will be essential. Again most of this stuff guys will have in their garage.

Remember too that I am using the Global Machine 80% shells in my pics and references. Though much of this process will be the same for other shells, many of the locating points and such are specific to *this* set of shells. BRP has a free download of their blue prints that I highly recommend for these semi mods as well, along with their downloadable semi auto manual which will help you understand this conversion and how it works.

Also as I mentioned earlier John's translated German manuals also will be a very important reference as well. If you don't have a set of his manuals please get them before going any further, its the only way you are going to to fully understand a lot of this upcoming info if you are a first time builder.

So lets begin; Welding the shells.

Using the Global Machining receiver shells required very little fitting so far as width. Check using your dial calipers, check your inside and outside widths and compare to your receiver shroud and or the rear MG3 stub section. They should be very close on ID.

Before welding IMO you should take the time to cut out your charging handle opening. I think it is easier at this point to get to this from the inside with a dremel and cut off wheel, at least rough it in for later. Doesn't have to be exact, just opened up some. It could be done later, but IMO its easier to at least get most of it cut now from the inside. We'll finish it when we get to the charging handle steps. Leave it on the small side for now so we can smooth it out and bring to size later.

A few pics;
Inside rough cut

outside rough cut;



A lot of the tutorials tell you to make the buffer cut slots on the inside before welding. I won't be doing that because we will be using a short cut there and it will not be necessary. We are going to cut the rear section off and splice a German rear stub onto the GM receive, complete with buffer cuts, buffer plates, rear most cuts, buffer stud and remnants of a charging handle slot already there.

So that said, you can make you own rear buffer area and get it all lined up, milled and riveted...or you can cut and splice on an in spec German rear stub. The choice is yours. But this is what we will be rolling with.
The rear MG3 stubs can be bought at RTG BTW.

Here's the latest one I got from Robert along with a nice brown tint bakelite German stock:



Back to welding the receiver;

In order to keep heat to a minimum and avoid warpage, only weld the areas that need to be welded. In other words there is no point in welding up seams where you are going to cut out the ejection port, grip stick slot, almost the entire top side will be cut out, though a tack weld in the center is advised. Mark out the areas to weld and not weld with a Sharpie or paint marker. This does not have to be exact and a little weld over lapping into these "no weld" areas is a good idea in case you rough estimates happen to be off. Approximate where the opening will be. Once marked out, V-notch the welded areas to be welded. Clamp it together. Then stitch weld, alternating, working from the center out to reduce stresses from the welding. Allow it cool from time to time as well as we discussed earlier in this thread.

These are just scotched taped together at this point BTW.
If in doubt you can use the free BRP blueprints we talked about prior:



Once marked we can then cut bevels into the welded areas for better penetration, then clamp it together. didn't go all the way to the ends because they will be cut of using the rear stub mentioned.



Next step will be squaring both the shrouds rear, figuring where to make the cuts for the splice and square the cut for the receiver to shroud using hand tools.

[roadrunner]

Nice work Der Alder,
It is time to breathe new life into the build topics. You should consider reposting this in a new thread so it doesn't get confused with the brp title. It deserves it.
I am working on an mg1 and mg74 clone right now. Want to get a bit further before I start the thread. Trick is remembering to bring the camera to the shop.
Rodom, keep up the good work. Nice progress.

[rodom]

Der Alder,
Thanks so much for the layout for "weld" and "don't weld". I see the raised area's on the bottom of the shells are being welded together.. I thought most of that would be cutout for the grip stick? Or is it just for support thru the cutting process until the opening for the ejection port and gripstick are cut?
See so many questions and so few answers to a novice like me. I ordered another rear section, but after looking at the one I already have, it would be great if I could open up the bent areas. It's so long I can set the rear of the rails using it.
And everyone who has posted has the same thought, Der Alder should run with this thread, and Salt6 needs to move it to the proper area, because it's going to be a great tool for any new members looking to stretch their abilities on a project like this.

[rodom]

Der Alder,
I really think we need you to add numbers - even rough ones - to the weld/no weld layouts. And the same for the cocking handle cut out. I've already purchased the manuals from John, so if you could do page references where ever applicable it will really help a novice like me understand the bigger picture. I've also printed out the excellent documents from BRP and Brian has been very helpful in putting them on line at their website. Once you have assembled this documentation, the suggestions and guidance from fellows like Der Alder are made much more clear for us noobs to follow along.

[Der Alder]

Road Runner and Rodom have me thinking,,,
Those are good points they make. I didn't really think about the fact that the title of this thread is "receivers from BRP", then we have since changed courses from the beginning and are now using the GM shells. That might be confusing to someone just walking into this.

So with that said, I think I'll start a new thread in the MG42 build area and transfer some of this info and add a lot more. I'm taking pics of my current build (an MG1 clone) and still have a lot of pics from my last MG3 clone, maybe I'll combine the pics and add the needed text, starting from unboxing the kit all the way through test firing and tuning. Maybe add some videos as well.

Rodom go ahead and keep this thread going with your updates and questions and I'll begin a new tutorial. I'll giving you some numbers on the openings you asked about. I'm on my way to work right now and will get those posted tonight.

Good luck
Tom

[Abominog]

NOTE!! For Yugo kit owners

Adler's approach uses the barrel bushing from the MG3 variant as well as an MG3 rear section w/ the buffer tabs.

The Yugo M53 buffer will NOT fit up with the MG3 buffer tabs (or the MG42 for that matter).

[Der Alder]

NOTE!! For Yugo kit owners

Adler's approach uses the barrel bushing from the MG3 variant as well as an MG3 rear section w/ the buffer tabs.

The Yugo M53 buffer will NOT fit up with the MG3 buffer tabs (or the MG42 for that matter).

I used to think that the Yugo buffers would not fit either till I tried several. Actually many Yugo buffers will fit the German MG3 rear stub. I have a sample in front of me as we speak. Of course the MG3 buffer fits like a glove. I just tried a Yugo buffer from my most recent M53 kit and it fit nice as well; only it must be turned from the other side.

With the German stock/buffer, place the top of the stock to the left, then turn to the right (up). (makes sense as it clears the longer MG3 recuperator). Whereas with the MG3 rear stub and Yugo stock/buffer, place it into the rear with the left side of the stock facing up and turn to the left (up).

Course this would not fit with the long MG3 recuperator installed because it does not have the clearance cut, but if running an 8mm type recup it will work. I do have another Yugo buffer that is quite snug, but will turn and fit. Then I yet another and it does not fit at all.

So I'd say *some* Yugo buffers will fit right into the MG3 rear stub, some may require some fitting, some may not at all without major work.

But of course the stocks themselves do not interchange as they have a different thread pitch. But odds are about 1 in 3 your yugo buffers may fit the MG3 rear (using my sampling), that is so long as you plan on running the 8mm type recup. If running the MG3 recup you may as well get the MG3 buffer and much nicer German bakelite stock IMO.

Here's a pic of an unmodified Yugo buffer that fits perfect in the MG3 rear.

And the MG3 type for comparison.



I'm not saying all the Yugo buffers will fit the German MG3 rear,but I guess the answer is *some* Yugo stocks may fit the German MG3 rear, some may not.

[rodom]

I'm hoping to be able to use the MG 53 stock, as I've already begun refinishing the wooden stock. Didn't I see in one of the older posts/builds that another builder had the problem of the Yugo buffer not wanting to fit, and he turned the buffer down a bit to get it fitting correctly?

[roadrunner]

I grabbed some buttsocks and buffers to check this out.
All three of my Yugo buffers fit well in the mg3 receiver stubs.
However swapping Yugo buffers into german and Austrian stocks is tight and leaves a gap.
Attempted mg3 buffer into three Yugo stocks and none started.
Just another bit of trivia.

[Der Alder]

I'm hoping to be able to use the MG 53 stock, as I've already begun refinishing the wooden stock. Didn't I see in one of the older posts/builds that another builder had the problem of the Yugo buffer not wanting to fit, and he turned the buffer down a bit to get it fitting correctly?

Keep in mind though if you are using the 8mm type recuperator and the yugo buffer fits you are ok, but if you plan to use the MG3 long recup either the M53 buffer will need a clearance cut or you will have to use a MG3 buffer. Myself I prefer the MG3 buffer only because it allows me to use the German bakelite butt stock.

[Der Alder]

I grabbed some buttsocks and buffers to check this out.
All three of my Yugo buffers fit well in the mg3 receiver stubs.
However swapping Yugo buffers into German and Austrian stocks is tight and leaves a gap.
Attempted mg3 buffer into three Yugo stocks and none started.
Just another bit of trivia.

Road Runner, not to derail this thread, but I'd love to hear more about your upcoming MG74 clone build perhaps in another thread.

I was considering doing one of these as well not long ago.
With my limited garage tools I can't get past the coolest part of the MG74, its front end with its cooling fins, which IMO make it the coolest looking MG42 variant of all.



Not to mention it was the only one that could fire selectively in semi auto. The green stock, grips and unique drums were neat too.




I had the idea of taking an MG3 bushing, turning it down as small as possible (for the inner bearing channels), then making a sleeve with the fins to slip over that. Problem is I don't have a lathe, I was thinking that would be doable. The rest would basically be a MG3 clone minus the AA sights (74 has its own optional type) with green stock and grip panels which can be found. BTW there is a MG74 G/S on GB right now if interested. The MG74 drums I've never seen available, but they were pretty neat too. They must be uber rare in the US.

[Der Alder]

Der Alder,
Thanks so much for the layout for "weld" and "don't weld". I see the raised area's on the bottom of the shells are being welded together.. I thought most of that would be cutout for the grip stick? Or is it just for support thru the cutting process until the opening for the ejection port and gripstick are cut?
See so many questions and so few answers to a novice like me. I ordered another rear section, but after looking at the one I already have, it would be great if I could open up the bent areas. It's so long I can set the rear of the rails using it.
And everyone who has posted has the same thought, Der Alder should run with this thread, and Salt6 needs to move it to the proper area, because it's going to be a great tool for any new members looking to stretch their abilities on a project like this.

To answer your question Rodom, the area on the bottom rear, behind the G/S will be where the bolt blocker goes, you could skip welding that part too being it will be cut out and the bolt blocker installed. I forgot about that part, but it won't hurt to weld that small amount.

There is also a small square cut out behind that where the grip hanger /recup support goes up through the bottom of the receiver. You could skip welding both of these areas as well so long as you had them layed out, then just weld on back. I didn't weld all the way back because I was planning to cut off the front and rear section being I was using the MG3 rear stub and my front shroud has and intact camming area. this is something new builders should take note of depending on how their kit was demilled and what parts you plan to use.

Again, this was just a very rough layout meant to minimize the amount of heat/weld used where it is not needed, You could over lapp some of these areas some and it would not hurt anything.

Once the bolt blocker is welded into place/ once you figure where it goes you can also weld the grip hanger over that, but thats later in the build which is why I didn't mention it.

One more issue to note if you are building with the rear MG3 sections I mentioned and also plan on using the MG3 recuperator, then you can cut the grip hanger off flush as there is no need for it to go up into the receiver as a recup support being the buffer plates will be doing that, so that is one less cut (square hole) into the bottom if making a post war type.

The BRP blueprints have many of the specs you will need so I won't bother listed them all. The ejection port is 6mm from the camming piece back and the ejection slot is 16mm wide for 8mm type slot. I make my .308 type a tad wider at 18mm (as did the post war Germans). If you follow the BRP prints on back it should give you all the specs you need. Let me know if you want something specific measured though and I'd be glad to help.

[rodom]

Okay I know it's not much progress but I did finally make my first cut on the receiver. As Der Alder suggested, I made the charging handle cut before welding the receiver shells together.

I also tried placing the charging handle into place, but the cuts haven't been made to the shell for the handle, so it's not going all the way to the frame. By the way, my handle seems to have a "bow" to it. Is this normal?

I hope you can see the bend I talking about. I guess the next step will be to weld the shells together and square the ends up to be mated to the shroud.

[Der Alder]

IMO at the point you are at on the build I would just get the C/H opening started and roughed in is about all I'd do. This is just to make it easier because to get the opening started with hand tools from the inside is easier, later all the finishing and final opening can be done from the outside.

On my last build I did the charging handle slot early, as the below pics will show, but IMO I think it may be best to wait till later after you get the grip stick installed after you really know how much clearance you will need there along with it relation to the semi bolt lug..and all this can only happen after the rails are in.

Not saying this is the only way, but as a matter of preference as a hand builder it just makes sense to me in this order to wait till later.

I'll list a few pics from my last build in that area. I didn't get a pic of it, but I used a dremel with stacked cut off wheels for the proper width of the C/H receiver slot, then when close to the right size I finished it with a small hand file. The nice thing about the RTG rear MG3 stubs is you can copy all the slots and cuts.

On the Ratchet plate, I used a Wiselite RP which already has the proper width slot cut into its back side, making it much easier for the hand tool garage builder, one less thing to deal with as a builder. The tricky part is getting the receiver slot the proper depth and width, along with grinding and milling the charging handle so that it fits, works smoothly, clears the grip assembly and catches the B/C lug. In a few spots you will most likely be breaking through the low spots on the receiver for the slot, this is normal, or has been in all the ones I've seen.

This is something you want to go slow and easy on grinding and fitting till it fits, when it is close use some oil to smooth out its operation. Some die-chem helps here too to show the high spots. IMO the charging handle semi mods are the most difficult part of this build, at least for me.

Here's a few pics to give you some ideas, you may find something that works better so far as tools, but this it what worked for me. I basically copied a Wiselite M53 I have using its C/H for a guide.

Rough cutting the slot to match the RTG rear stub's slot;


Using a hand file after the dremel with stacked cut off wheels to finish and smooth out the slot;


Comparing the modified C/H to an unmodified, note the width and area under the rivets;


Grinding on the C/H to get the width smaller;


"milling" with a dremel to remove metal under the rivets for clearance.


Fitting the modified C/H into the slot, this will take many attempts, go slow;


Test fitting holding it together by hand with RP just to see how close I'm getting. You can use C-clamps for this as well;


Another shot of the same;


Now this next mod may not be needed on some builds, but I noticed on my WL M53 they had an extension on the end (part added sticking out). What this is for is if the opening is too large, the C/H may pop out when fully retracted. The added length keeps it in place from popping out. Mine worked very smooth so I copied this mod and made my opening a tad large. Again this may not be needed, but I thought I would list it here case anyone has this problem and is looking for an easy solution. One thing to be aware of is you want this no longer than need be as if it were too long is could hit the barrel extension.


This should give you a general idea of what mods are needed. If you need the specs of the the C/H let me know and I can mic them.

[rodom]

Thanks Der Alder, my next step will be to work on the charging handle. Did I miss something in the other builds I've read on line? I had no idea the charging handle rod was too wide for our builds, so how much does it need to be narrowed? And sounding like a noob, why is this? Why does the piece need to be altered? Is the aftermarket receiver/ratchet plate tolerances off/skewed causing this? Just curious as to if there's an answer for this. Once I get the handle slot cut I'll prep the shells for welding.

[roadrunner]

Rodom, the charging handles always seem to take that set (bend). Years of yanking on em' I guess.
I have had good luck straightening them by just squeezing them in a milling vice. The brp prints show the
Dimensions of the c/h grooves and ratchet plate. With these you can figure the c/h width. Then subtract .005"
or so for clearence.
Der alder, on the mg 74 clone. I am doing just that. Sleeving an original style crimp on barrel bushing that I turned down. I'm turning a bushing and it will be a shrink fit and profiled after. I agree, they are the most refined version. "Cool!"
Like to find Steyr grips but 200 bucks for a buttwalked pair on gunbroker is just too much.
When I get some more done I'll start a thread.

[roadrunner]

Oh yeah, If anyone has a line on an mg74 belt drum and reasonably priced steyr grip panels or complete gripstick please let me know. Thanks