Link the videos below I’m sure people will appreciate. I never said I was an expert. I built the gun and it didn’t blow up. So I do have that going for me. I made the video because I couldn’t find any video’s on how to do one.

No hostility intended. Pick up an Armorer’s Manual. Fluted chamber floats the case, which pushes on the bolt, causing the trunnions to push the rollers in, which drives the locking piece back. The bolt carrier moves roughly 4:1 compared the bolt due to carefully engineered ratios/angles. Too much bolt gap, bolt carrier moves too fast. Not enough bolt gap, moves too slow. Cartridges and primers don’t explode. Primers burn with extreme brisance. The powder in a cartridge creates hot, rapidly expanding gases. The HK91 is a blowback, roller delayed. Design. If it was a simple blowback (like a 9mm handgun) the bolt would have to weigh 35 lbs. There’s much, much more to know. For the last 35 years I’ve searched for everything I could find. That’s how I found your video. Good luck with your channel. 👍

Thanks

@@adamsgunroom9331 Not everyone can even grasp these concepts, nevermind explain them. I've seen some CETME build videos that show some bad info and building techniques that are really questionable or just flat out wrong, which can be dangerous to the viewers. I think it's important that if you're going to put this stuff out here that it's correct. I think yours is exceptional. So thank you.

Thanks

I can give it a try. I am not the best at doing videos but I will do my best. Lol

@@adamsgunroom9331 Sounds good.. Thanks

You could press the barrel first but I welded the trunion into the receiver then pressed it in. I would weld the pins on the inside of the receiver. If you dimple the sheet metal in on the receiver you could weld it on the outside as well.

The only thing you can do is to drive out the barrel pin or press it out. Press out the barrel from trunnion turn your barrel 180 degrees. repress with proper bolt gap and then pin the barrel again. I think this is the best fix for your situation. I would take apart the bolt and measure the rollers for excessive wear. I would also check the locking piece for excessive wear as well. Good luck sounds like a fun project!

Could you not purchase larger rollers? +4,+6????

Bulge is concerning as it sounds like you are going to have a case failure. you might have too much bolt gap or a headspace problem.

Case bulging is seen as normal, but still probably able to be improved

I honestly don’t know why.

It’s not too bad if your mechanical. You will need some tools so if you don’t have a welder, hydraulic press, drill or drill press. It’s cheaper to just buy a ptr. Otherwise take your time and it’s totally possible

I just built a working 3d printed one using surplus parts not too hard

I will add it’s the cheapest build as well, so if it goes bad you are not out a huge pile of cash.

Not exactly because there could be some tolerance stacking occurring with the bolt itself. Headspace would be measured from bolt face to datum line in chamber. I wouldn’t use gap off back of carrier.

Through the comment section

The trunions are different so they are not interchangeable

@@adamsgunroom9331 ah damn, i knew i shouldve waited until i got a reply. i literally just dropped a bunch of money on a new bolt carrier, bolt head, firing pin and spring. do you know how different in spec the trunnion is? could it be corrected with larger rollers? i know theres lots of mixed opinions on this, but i want to suppress it. i got the 36° locking piece and wanted to make sure my bolt gap is in spec, but seeing how the trunnion is different, i dont want to blow my rifle up and probably myself in the process.

I didn’t use it. If I want to shoot irons I left enough room to add it later in front of the rail I welded to the receiver.

You can use negative rollers for example you can buy -3 rollers or you can pull the barrel pin turn 180 degrees repress and pin the barrel to proper spec

Thanks.