So I am in the works of planning out a 9mm build and I've run into a problem.

I want to build a 9mm AR pistol with the law tactical folding stock adapter. The problem I've run into is that the CMMG 9mm BCG, and other blow back BCG's designed for double feed mags, have some sort of an insert I believe in the rear end of the BCG to increase weight. There is an important piece of the law tactical adapter that is a BCG extender that needs to be put in the rear of the BCG to cross the bridge between the added distance. In the CMMG BCG it looks like there is a roll pin that is holding that piece in the back.

Here's my question. Can I punch out that roll pin and remove the extra peice of metal in the back so I can pop the BCG extender in? If I do what will need to be changed in order for the pistol to operate properly, a heavier buffer?

Thanks guys, I really want to turn this idea into a reality.

I would say email CMMG and ask, but I've found the answers less than satisfactory when using email for technical questions.  You may want to call CMMG and ask for a technical specialist.  I'm sure others have had the same question...

I have removed the carrier weight and the only thing I noticed was an increase in the cyclic rate on my M-16. The brass didn't look any different than when the weight was installed.

I would think that as long as the fired brass looks fine you should be ok.

You can remove the weight and put the piece in......but you will have to make the weight up somewhere else. Weigh the current bolt and heavy buffer......then when you remove the weight from the bolt you just have to maintain the same total weight of the reciprocating mass. (combined weight of the bolt and buffer) If you don't you are setting yourself up for out of battery discharge as in a blowback gun the mass of the bolt is what keeps the breech closed long enough to let pressure drop to a safe level before it extracts and ejects.

Does the weight have to be perfectly equal? I'm not understanding why that would cause an out of battery discharge. Bolt is closed, round in chamber, trigger pulled, hammer hits firing pin, round fires, pressure of round pushes bolt back correct? If less weight is there would I just have something similar to overgassing and a harsh ejection at like 9o'clock? I'm not firing full auto

Please correct me if I'm wrong, I don't have any expirience with blowback AR s

The weight retards the movement of the force on the rear of the cartridge; without it, the pressure of the expanding gas will cause the brass to leave the chamber before it is low enough to safely eject the casing thereby rupturing out the side of the brass creating an out of battery discharge. Like a miniature grenade next to your face. If this happens even faster, then the ensuing  pressure blead can cause the bullet to be lodged into the barrel wich will cause worse problems after the next round is fired. I.e. in blowback, proper weight is a good thing.