Elyott

Help please: I have a Belgian FN FAL that sometimes fails to feed. I have cleaned the gas system thoroughly and had the piston re-built to correct dimensions. I have tried every gas setting. I am using mil surplus fmj ammo.

The rifle is in good order.

You'll have to elaborate on 'feed'. Assuming that you have eliminated magazine faults, feed can only occur once the breech block clears the rear of the next cartridge in the magazine. If it dont, then it won't. And if it don't, adjust the gas so that it does. NOW, if you can't get the breech block to return to the rear I can guarantee that you have a split gas cylinder