i assembled a 7.62x39 16" mid-length gas-system barrel, with a piston conversion, and had to open up the gas port to 9/64" (.1406") in order for it to work reliably with a 4.1oz buffer (1/8" hole worked fine with 3oz bfr).  i'm just wondering, as the bullet passes that big hole in its travel down the barrel, does that affect the bullet stability?  in my initial function check, it seemed to be pretty accurate, red dot at 50yds.  haven't tried it out at 100yds yet.  i guess that would be the real test.

i wanted it to work with the 4.1oz buffer so that the assembled lower remains swapable with my other upper receivers which function with the ST-2 4.1oz buffer.

the 9/64" is still smaller than the mating gas port hole in the piston gas block.

the alternative would've been to drill out the 1/8" hole in the piston gas plug, that's the smallest constriction in the gas flow to the piston, but i didn't want to do that because then that gas plug has to be dedicated to that barrel (future swapability, etc).

just wondering...

Which piston did you use?

Adams Arms.  not an issue with them.  this is totally my own science project to take a 5.56/223 optimized conversion kit and get it to work with 7.62x39.  i have a few AR's with AA kits on them, quite pleased, otherwise i wouldn't have chosen their kit for this 7.62x39 project.

NO.

lysanderxiii:  ok.  thanks, much appreciated.

I had to punch out the gas port on my Huldra to .090.
http://www.ar15.com/forums/t_3_126/661003__ARCHIVED_THREAD____ADAMS_ARMS_mid_tact_elite_won_t_go_boom.html&page=1#i6702318

No effect on bullet stability and a market in increase in functionality. :)