AR Tuning question

[brutus1776]

Pulled block. Mic on hole was showing .076 best I can tell. I then got a thing piece of plastic stock and worked it circularly into the hole, then mic’ed it and got .077. The gas ring around the port is exactly centered.

 

[msgriff]

Thanks
The bcg I put in is also a bcm albeit with about 25k rounds on it.

What the port size need to be to not wear out rings fast in those round counts? I can’t be replacing gas rings after every class or every few training sessions if this is the problem.

Gas rings are only half of the bolt's gas system seal. The other half is the tail of the bolt and the corresponding bore of the carrier. It's a very tight tolerance fit, and I wouldn't be surprised to see it out of spec on a 25k round count BCG/bolt/carrier. The only way to check is with specialty pin and ring gauges.

 

[brutus1776]

The 25k plus bolt is the bolt that works in gun. The new bcg with a little under 2k doesn’t work.

 

[mettee]

Its crazy that you put an older bcm bcg in and it worked.

Something is up with the original one for sure.

Can you try the brake now with good bcg, or did you already do that

 

[tomme boy]

The internal specs of your bcg are f'ed up. The rings are only a part of the system. Swap the carrier that works with the bolt that does not. That will tell you everything you need to know about what is going on. If it works then your newer carrier is the problem. If not then it is your bolt causing it.

And to just prove it, swap the bolt that does work into the carrier that does not right now.

Just make sure which parts go where they need to.

 

[brutus1776]

Its crazy that you put an older bcm bcg in and it worked.

Something is up with the original one for sure.

Can you try the brake now with good bcg, or did you already do that

Yes, did this Sunday and got lock back with noticeably more gas/recoil, and was able to tune the gas block a bunch of clicks before no more lock back

 

[brutus1776]

The internal specs of your bcg are f'ed up. The rings are only a part of the system. Swap the carrier that works with the bolt that does not. That will tell you everything you need to know about what is going on. If it works then your newer carrier is the problem. If not then it is your bolt causing it.

And to just prove it, swap the bolt that does work into the carrier that does not right now.

Just make sure which parts go where they need to.

I’ll try this this weekend.

 

[TonyAngel]

sounds to me like the gas port is drilled from the manufacturer for a non-adjustable gas block - too small. I suggest you open up your gas port a little (.015" -.020") so that you can use your adjustable gas block to its fullest across your possible combinations of buffer weight, buffer spring tension, and cartridge data.

Whoa there. Are you proposing that he drill the gas port out by 15 or 20 thou?! No, no, no. Even if that is the problem, we are at the fine tuning stage. .003 at the most. If you put another zero in there after the decimal, it makes more sense.