Receivers from BRP

[rodom]

Well fellas I'm to the point I need some assistance from the builders out there. I have my semi bolt conversion welded together and need some instruction on how to properly assemble the BRP bolt kit. Does anyone have this procedure saved to a previous string or sticky? How about a .PDF? I really would like any information you might have, as this is my last step before assembly for test firing.

[rodom]

I've gotten the bolt assembled from the BRP kit, and have the charging handle setup and working. I'm trying to setup the bolt, but the recouperator seems to be too long. It's seated against the rear buffer pad, but with it installed, I cannot install the barrel. It hits the plunger on the recoup. The front plunger on the recoup appears to be about 1/4" too far forward.
Also, the bolt and tab for the charging handle seem to be rubbing on the mounting bracket for the recoup. I've tried tweeking the mounting bracket this way and that, and was curious as to if this was kinda normal. The charging handle just barely contacts the tab welded on the bolt, and I was thinking the tab on the bolt might need to be extended, but with it hitting the recoup that might not be good either. I might need to weld a small piece of metal to the charging handle to make it a bit "taller" to insure contact.
I had a friend weld the bolt extension for me with his TIG machine because I didn't want a failure. I managed to screw up the rear post for the bolt, trying to press it in. I didn't realize it was oversized, so I crushed the first one. I called BRP and ordered two, so if I screwed up again I would have a spare. If I ordered one I would have screwed it up, but ordering two insured that I wouldn't make another mistake.
I added a couple of features from the Oak Rodent build that I thought we good. I used his idea of building up a tab on the ratchet plate and adding weld to the "hook" on the charging handle to form a bolt hold open when the handle is fully retracted. It looks like it will work well. I had seen other builds where guys added FAL parts to duplicate that type of bolt hold open, but this just seemed so simple and clean that I decided to try it.
I also used the idea from Mech Warrior at Weaponeer of drilling an access window in the bolt extension so I could see the hammer/firing pin contact.
There seems to be several new members on the website, and they are staring their projects too. I'll post some pictures of the damaged rear post and such in a bit. Everyone can learn from my mistakes too.

[along]

I am just starting my build actually, however I am not at this point yet. I bought a BRP semi auto bolt parts kit and trigger assembly. I put a semi bolt from apex gun parts with the extension and charging handle tab welded on. I am still doing the front shroud work. I can provide measurements of the tab on my bolt if that helps at all

[rodom]

I've run into another problem. The BRP trigger group is hanging up the bolt's motion. With the bolt installed, no recoil spring and the trigger group installed, I'm getting very good hammer to firing pin contact. However the hammer sticks up too high , even retracted in the cocked position, for the bolt to move to the rear after firing. I have seen one or two builds where the builder grinds off some of the upper body of the hammer itself, and was curious as to if this was standard procedure. It does look like some of the hammer will have to come off for it to clear the bolt extension. Any others out there have this problem?

[rodom]

Hi Along, sorry I didn't respond to your post. There are a number of great builders here who are willing to help, so just keep trying and asking questions. I took a couple of pictures I hope will explain my question about the necessity of the hammer being trimmed back

I know it's hard to see, but the contact patch from the firing pin is almost centered in the hammer's face, and it does make a good contact - nice and square. The next picture is a side view of the hammer and you can clearly see the mark I made to indicate where the hammer strikes the firing pin.

My idea was to leave about 1/8" above the contact area, and then trim the hammer back into a gentle arc to remove the excess metal that's hanging up on the bottom of the bolt. I have seen AR hammers before, but this one has a hook on the tail of the hammer that I haven't run across before. I'll end up cutting it off as part of the trimming. We need to have some of the more experienced builders give we newbies a little more detail on some of the finer points of the bolt assembly and fire control group. The only build file I saw anything about trimming the hammer was in the Mechwarrior posting, and only because he had trimmed too much and had to weld up the face. that's the great thing about steel, if you cut too much you can always add more metal back on.

[along]

Hi Rodom,

no problem, I figure most people on here have got jobs, responsibilites, etc. and we're all trying to squeeze in this build for enjoyment. I went over that mechwarrior build several times, but it got pulled recently and I don't know why!?!?! Do you have the build in pdf form by any chance? I thought it was a pretty good tutorial. thompsonmachine.net also makes a mg42 semi auto gripstick, maybe ask for him hammer dimensions?

[rodom]

No problem along. The Mechwarrior build was on the Weaponeer website - the link is http://www.weaponeer.net/forum/forum_po ... PN=1&TPN=1. Try that and let me know if you can find it. It's a very good tutorial, and the photos are excellent.

[along]

oh thanks for the link it works! additionally i was thinking maybe welding a small square or rectangular piece of steel and then grind it down, as opposed to just slapping weld on it. just a thought, let me know how it goes as i have a brp semi trigger group too

[rodom]

To my knowledge, the hammer only really needs to be ground down a bit to allow clearance. The Mechwarrior build, when you read his captions, explained that he modified the hammer before he had a working knowledge of the bolt/hammer relationship. With Der Alder's permission, here's his modified hammer.

As you can see it's much different than Mechwarriors, and much more modestly trimmed. If he's out there, I would like to hear from Mechwarrior, and to thank him for his excellent tutorial. It has helped me much during my build.

[along]

thanks for the picture, I'll make sure to measure it to mine when I get to that stage in the build.

[rodom]

Here are a couple more photos of the additional ideas I have been given by others. Der Alder strongly recommended the charging handle "kickoff" mod be added to assist in breaking the bolt rollers free from the camming area.

Also, the mod for the charging handle to be locked open from Oak Rodent seems to work well. For just a little welding it's a lot less work than some of the more extravagant methods some of the other builders used. The one by Mechwarrior is great, but the one I used is simplicity in action.

As you can see, I'm getting very close to having a working semi auto. One thing I would like to pass on to the new builders out there is that I had to trim the recoup more than I originally did. The edge of the mounting area was hitting the bolt and causing drag, and I didn't find it until I painted the bolt with red dycum to identify the effected area and track down why. Since I had thinned the rails, thinking they were causing the drag, I might have to cut a shim for them to remove some of the play. I also want to let the other newbies out there know about the amount of effort it takes to cock the rifle. The rollers once deployed and extended into the camming area by the bolt take more than a little effort to compress back into their seats to allow the bolt to be cycled. Since I had never shot anything like the M53/MG42 I was completely unaware of this, and that's why the pushoff area on the charging handle cutout is a necessity.

[along]

Thank you for the pictures, very clear.

where exactly is the kickoff mod in the picture? I am still learning all the cutouts and functions of the receiver so I'm still a noob at this.

Also keep up the good work, your'e getting close to it being finished it seems. I'm still trying to figure out what shim stock to buy to head-space my barrel to my barrel extension. I've got my go and no-go gauges for fitting. I've been looking all over amazon for what steel shim stock to buy, I guess the smaller thickness the better? Smallest seems to be .001''. Thanks again for the pictures. Also how exactly is the recuperator trimmed?

thanks.

[rodom]

Thanks Along. Yes you do want the thinnest possible shins. Granger Supply is a great place for that type of supply, and you can find them on the internet. The built up area by the charging handle is the push off I created. I welded some scrap metal in and then built up weld around it so it could be ground down to like what you see. If you look at your shells, there shouldn't be like it already on it. The arm on the charging handle - when pulled back to cock - pushes against that area to give leverage to the handle. As you get further into the build these things will become more self evident.

[along]

oh I see so the pushoff area is that ramp?

the bold hold open doesn't seem too hard to install, was it?

yea man I figure just more and more research (and building of course) will open up a lot more understanding.
I still haven't really looked into how the recuperator works.

[rodom]

Along - if you go to the Oak Rodent build, you can see how easy the bolt hold open was to create. A small piece of metal, a little careful welding and then a Dremel tool to cleanup the weld is all you need.
As for the push off area, just click on the picture and enlarge it. Then compare the picture to your charging handle and you can see what it does, how it uses a finger to push against the area I welded to force the bolt rearward.
Some of the same scrap steel I used on the bolt hold open was used on the push-off area construction.

[along]

is there a pdf or forum of the build? I'm sure there is I just couldn't find it when searching for it

[rodom]

Along, it's the very first string in this "build" section. Page 1, item 1.

[along]

ok thanks rodom, I didn't realize it was oakrodent's build but I have actually started looking at this build before.

[rodom]

Ok fella's it's bragging time. I fired my project for the first time today. I followed Der Alders recommendation and test fired the gun with primer only brass, which allowed me to check the feeding and ejection of empty cases. The primer only brass had excellent primer strikes, well centered and strong. Ejection and feeding were as they should be, without mis-feeds (even without a bullet to help guide them) and emptys dropped out the bottom without issue.
After testing with empty cases, I loaded a started tab with one round, set it next to the feed stop and closed the cover. Racking the charging handle, the round fed in as normal. Then I pulled the trigger, which fired the round and ejected the empty brass. Next, I loaded two rounds into a starter tab, and repeated the procedure. Bang, bang and no problems. Each fed and ejected just like it should. The next step was loading five rounds into the belt. Each was fired in a slow steady pace, and each round ejected and loaded as it should. Then I took the testing further, with 10 rounds loaded into the belt. I don'r need to tell you guys how cool it felt to watch the belt feed in and listen to her bark.
Back to the shop, and I inspected all my welds for cracking. I'll tear her down and give everything a good cleaning, but so far the welds look like they are holding up just fine. One thing I did notice, the rifle is rough on the brass. The shoulders have a fairly large dent in them, but I'm hoping re-sizing them will pull some of that out. Der Alder recommended using surplus ammo, but I couldn't find any locally (or quickly) so I used the white box Winchester, which is listed as a military over-run by Midway USA.
I haven't tried firing from the Lafette yet, so there's more to look forward to. And let me finish by thanking all of the members out there who's help contributed to the successful completion. Der Alder, Road Runner, thanks again for the advice and "coaching" thru this. Without you guys, I would never have finished such a complicated and difficult project.

[JBaum]

Another MG42 lives! Now when someone brags about building an AK or FAL, you can just smile. You've done what few others have done (compared to building other guns).

I have seen AR hammers before, but this one has a hook on the tail of the hammer that I haven't run across before.

The tail is because it was an M16 hammer, not one for an AR15 (no tail). Best to cut/grind it off, so there's no "full auto parts" crap from anyone. The sear holds that tail (which holds the hammer back) until it the bolt moves forward and pivots the bottom of the sear rearward, which then releases the tail. That keeps the M16 from firing before the bolt is fully forward in full auto fire mode.