Receivers from BRP

[rodom]

And I'm still trying to make progress. I got the shroud squared up, and the receiver shells tacked together. I had to split them apart and use the belt sander on them to narrow them a bit. The shells as delivered were 2.235" wide, while the specs call for them to be 2.20". I touched them up and got them down to 2.210" but I wanted to leave them a bit wide so the bolt will have plenty of clearance.

I also am using the MG3 rear stub from RTG , per Der Alder's building tips and shortcuts , so I have that cleaned up and ready to use. It's squared up and the stubs of the rails and rivets are gone. I don't know why the 2ndpicture looks so out of square, it's really quite square.

[rodom]

The receiver shells are welded and ready to be cut to length. I've been tinkering with the ratchet plate, and after purchasing one from Wiselite with the slot cut, I used it as a template to cut the slot on the one from Global. I git the slot cut using Der Alder's trick of stacking Demel cut off wheels to get the groove size I needed. After doing this I tried to fit the plate to the charging handle and found the bottom of the plate hits the handle. I trimmed it down and now the tab on the handle fits nicely into the groove on the plate. So now I have two usable ratchet plates. Can you see where this is header? I'm gonna wind up with two of everything and HAVE to build another? Oh NO Mr Bill!

[Der Alder]

Looks like you are making good progress. Just keep going slow and taking your time as you have been and you will do fine.

By the time you are done, being that you are doing a a .308 conversion you will have a lot of spare parts.These builds are addicting BTW. Thats like I had more than enough spare parts after a few builds to do another minus the shroud...then Apex offered shrouds for sale (picked up a nice one), so now a whole other kit minus a couple small odds and ends. I'm just glad I bought several barrels over the years as they are getting expensive.

The big hold up for me right now is the semi auto bolt carrier. Still waiting on BRP to get them in stock. I've had good luck with the BRP semi parts. I talked to Brian and he said their bolt carrier supplier went out, so now they will be making their own B/C's in house again on their CNC machines.

[rodom]

Well I got the shells welded, and the welds ground down and it's looking good.The ends of the receiver weren't smoothed out as much as the rest of the receiver, as the camming area is excess, and the end will be cut off and replaced by the receiver end stub I purchased from RTG, as one of DerAlder's time saving short cuts.

I started the cutting, by first cutting the front section, removing the excess from the camming area. After I got this area squared up I started to fit it to the shroud. Der Alder warned me this is time consuming but he didn't mention how nerve wracking it can be. It took me two days - not 48 hours but spread out over two days to get the shroud to receiver fit where it needed to be.

Hopefully tomorrow, I'll get the shroud and receiver tacked together so I'll have something solid to work with. The next step will be to cut off the end piece, after careful measurement, and square it up so it can be connected to the new read stub. The stub is already square, so once the receiver is squared I can get it tacked together.
I need to find a good 8mm barrel, so I can have enough parts to be able to shoot both calibers. I think Apex has barrels, but without the barrel extension. My extension that came with my kit was kinda messed up when they torch cut it, but I'm hoping to be able to use it. I'm not even half way done with the receiver and I'm already thinking about shooting it, NOT too excited, HUH?

[rodom]

Moving forward, I tacked the front portion of the shell to the shroud, and began to fit the rear stub.

I wanted to make sure the overall length was still within specs.

Sorry about the upside down photo and glare, but at this point I'm 1/16 over. After final fitting it was right at the 37 11/16" spec. Per Der Alders recommendation, I have 29mm between the back of the camming window and the front of the first cover pads.
Now for some more "V"ing of the areas to be welded and then the welding itself. I just couldn't help myself so I did a quick mockup to show some progress.

[rodom]

Okay I'm throwing this out to all the membership and anyone bored enough to read this. Der Alder has been kind enough to coach me on the receiver and shroud fitment, but I would like to hear from others out there as to how you were able to get the two major components squared up and straight.
From my pictures you can see ( I hope) I was able to get the two mated correctly. This was done with a string, a level, a square and a lot of swearing. Next time (see, I'm already hooked) I'd like to do it with less swearing. Not that I'm a prude, I'm actually pretty good at swearing. Just ask anyone who knows me. But it's rough on the digestive track, and my wife's nerves. So I'm open to any ideas as to how to make this step more of a no brainer, and less of an aggreviant. I think I just made up that last word because my spell checker choked on it. Anyway, this is for the benefit of our membership as all of this is public domain stuff, including my new word. Has anyone calculated the taper of the shroud so we could place incremental blocks at key points to allow the shroud to remain level at all times? I gave this a lot of thought but couldn't get it worked out in my pea sized brain. I thought about assembling the barrel and bushing in the shroud and place a wooden dowel rod in the barrel long enough to go from the breech to past the muzzle so you could place a small bubble level on it. Once this was leveled the receiver could be butted up and marked. Sound good? It's simple enough for almost anyone to do at home. If the taper is even on all four sides this should work for the "left, right up and down" needed for the proper receiver fit.

[ScottishTerrier]

This is an excellent thread. Keep up the good work rodom and der alder. The shortcuts and current build tutorial are extremely helpful. Can't wait to see how der alder does his cuts and drills his holes.

[Der Alder]

Lookin good man. I've been away again for a few days. Just popped in to say hi and that we are getting ready for white tail season here in NW PA (its a national holiday here lol), even the schools are closed mon.

Glad to see you making progress and taking your time Rog.

We'll catch up later.

Tom

[rodom]

Small steps and plenty of them I still need to make. I differed the actual welding to a friend who has a TIG machine, my last shots were of the shroud and receiver tacked together using my MIG. After the receiver and shroud were welded, I cleaned up the welds.

After everything was smooth, I laid out and made my cuts on the top surface.

The BRP blueprints call for a 15 degree cut to be made to the center channel on both top and bottom edges. Anybody has any insights into making this cut? Do you have a method, or is it just a SWAG? (Scientific Wild ASS Guess?)
After making my cuts, I fit the camming piece onto the shroud, and got a nice tight fit, while still being able to pop the rivet thru the window. The small camming piece had to be tapped into place with my plastic mallet.
And then I fit the feed assembly and top cover, getting it close enough that the cover actually latches closed. This last shot is with all the above components in their proper places.

The next step will be the lay out and cutting of the bottom openings. One question on that, does anyone use the ejection port cover? I have viewed several tutorials of other builds, and I don't see where anyone has mentioned installing or using it. I'll be cutting the ejection port, trigger opening and semi auto blocker opening. Since I'm using the MG3 rear section, and the MG3 recuperator there's no need for the square hole behind the trigger opening.

[rodom]

Der Alder, I know what you mean about Deer Season. I used to work for a fellow who owned a stamping plant in Cory Pa. He HATED Thanksgiving, because the following Friday he would NEVER have enough employees to run the plant. He started giving the day off by default, because he knew he could never get his workers out of the field. Good luck to you.

[rodom]

As I was laying out the bottom cut lines for the trigger and ejection port openings I had a thought. The BRP blueprints I'm using are fairly old, I'm guessing from the time of Brian's first build and first generation trigger and bolt. As such, have there been any changes to the templates for the new second gen trigger stick? Do the openings stay the same, or have they been modified? I haven't really heard anyone reference these changes as any kind of update to the blueprints. I've included a photo of my bottom side of the receiver with my openings defined and marked for cutting. The trigger opening has several special cuts that I'm not sure are needed now with the new trigger stick. Can anyone offer some insights?

[roadrunner]

Rodom, the radius cuts in the ejection port are used for the twist in lugs on the semi gripstick.
You will need these for sure. I used the trigger adapter from brp and at 25 dollars it can't be beat.
I'm pretty sure the same dimensions apply for the aluminum gripstick. I would stick to the dimensions
Brian has laid out as there hasn't been any dispute previously.
Your making great progress.

[rodom]

After laying out and cutting the openings for the ejection port and the gripstick, I cleaned up the cuts and dressed with a small file.

This was my first attempt to fit the grip.

After many attempts to find a solution, without success, I started to re-read all of the other build posts. I finally came across the build from oakrodent(?) who mentioned that the back section of the ejection port from the circular cutout to the bottom of the port needed to be opened up to 18mm. I measured my grip and that area is .730" or slightly more than the 18mm listed which is .708"
So after expanding the bottom end of the ejection port to .730" I was able to seat the grip properly.

I was checking my distances from the rear of the receiver to the back of the grip, and I'm finding it's a bit short as compared to the blueprints from BRP.
It should be .570" from the rear of the receiver to the pin hole on the gripstick, where mine is currently only .550"

Going from the large pin that's part of the recoup support, it's about .012" short. It should be .420" and mine is about .408"

So at this point I think my trigger stick needs to be moved forward about .020" or so to get the gripstick closer to where it needs to be. Here's a shot of the front of the gripstick and how it's fitting into the notched area.

Any advice from the membership is always gratefully accepted.

[roadrunner]

Rodom, If I understand right, you don't have your bolt carrier yet. You want your hammer to be square with the rear of the carrier where it contacts the firing pin. I would hold off on fine adjustment until you can mock it up and see the angle of hammer contact and go from there. A lafette is also handy because it is a good gauge for that length.
Nice job so far.

[rodom]

Yes you are correct in that I don't have a bolt carrier yet. I have been in contact with Brian at BRP inquiring as to if he might have an ETA on his second gen bolts, but he's not sure. He was also kind enough to offer advice on the trigger group fitting. I had spoken to Der Alder about this, and he suggested the Lafette as an option to aid in grip location.
So I ordered one the other day and am waiting for it's delivery so I can rough in the gripstick location. I believe I'm going to have to look into the bolt kits that BPR sells as an option to their 2nd gen replacement bolts. Does anyone have much experience with them?

[rodom]

While I'm waiting for my Lafette to arrive. I thought I would start working on the receiver rails and recuperator. So an open question to the masses, whem the rails are installed, do they go so far forward in the receiver as to touch the camming piece, or is there a small gap left between them?
I've been using DerAlder's shortcuts, and one of them is the MG3 rear receiver section since it has the buffer pads already installed. The spacing is a bit different for the rivets on the MG3 stub though. The BRP prints show 2.869" from the rear of the receiver to the first rivet, while my stub has a rivet at 2.945". Should I stick to the prints or go with the spacing found on an actual receiver?

[roadrunner]

There was some discussion on how far forward the rails should be on my" new m53 build" thread. The consensus was as close as possible. This way the d-holes back up the cam piece. All my cam pieces show finish wear from rail contact and others saw the same thing.
Are you using new undrilled mg3 rails? Rail holes don't seem entirely consistent between manufacturers.
I verified my ratchet plate location as a guide for the rear ones and used the print for the rest.

[rodom]

Hi Roadrunner,
Thanks for the feedback. My gut was telling to get the rails as close as possible, as a gap might cause problems with the bolt moving at the speeds that even a semi-automatic will move at. Yes, I'm using new undrilled rails from BRP, but I did use my old rails as a template to drill and tap the new ones with. The new rails seem to be a bit longer than the MG53 rails, so I think they'll need to be trimmed to clear the buffer cuts inside the receiver. I'm in the process of laying out the locations for the recoup, and the left and right side rivets. I'm going to use screws as DerAlder advised, as I like the idea of being able to remove and replace the rails easily. I'm going to cut the "D" holes and drill only the rear rivet holes, so if the rails aren't close to the camming piece I can weld the hole shut and redrill in the correct location.
I've already trimmed the recouperator down, and once I get the Lafette I can mark the gripstick and drill and mount the rear bolt for the recoup. Once that stuff is done, I'll need to decide if I'll purchase the BRP bolt conversion kit, or wait for the 2nd gen bolts. I wish I had a clue as to how long that might take. And of course I'll need to decide on a finish. I guess parkerizing is close to the original finish, but I did hear someone say there were blued samples too. I'm leaning more towards bluing right now.

[rodom]

So I got the recoup cut down and wanted to get it mounted in the receiver but as shipped the front mounting bolt wasn't installed. No big deal, right? Wrong. I can't keep the bolt in place with the crimp that is on the tube of the recoup, along with the bevel on the bolt itself. i tried the mounting bolt from the MG53 recoup, but it has a double sided curved piece that won't go under the crimp either. Does this crimp need to be removed before the bolt is installed? I've included a couple of photos to explain the problem, and I'm certainly hoping for feedback from the builders out there.

[rodom]

As I'm still waiting for the Lafette to arrive, I been trying to mount the rails inside the receiver, without much success. For the past two days I have tried to drill and align the mounting holes in the frame for the rails, and made a mess of my receiver. I'll need to weld up some of the holes after I get everything straightened out.
I used my MG53 rails as a template and drilled and tapped the holes in them as Der Alder had advised. I tried using the specs from the BRP .PDFS, but it didn't quite work out as planned. Anyway, after getting the rails mounted reasonably straight and level, I tried to drop the bolt head down thru the rails and to the camming piece. It stopped just at the camming piece and had to be forced thru (no barrel) to the shroud. I removed the rails, and the bolt head falls right thru the camming piece, so I know there's no problem with it. I have tried to align the rails as seen in some of the other builds, with the top of the pad on the rail level to the larger pad on the camming piece. When that didn't work I tried moving the front of the rail up and down as it relates to the camming piece, and I could make it worse, or tighter, but never eliminate it it has to be pulled with some effort thru the camming piece.
As always, I'm looking for someone who has "been there and done that " to advise me as to what is wrong.