I use 4" calipers to get my size. The 5/64 is a 0.0781. I would take it to the min of 0.093 or a 3/32. If it needs more, the take it to a 7/64 (0.109)
Sounds like its making a good seal, but the port is just to small and the gas is getting out the barrel and not the port. If you drill it out, make sure you put a cleaning rod in the barrel first so do do not drill the bottom of the barrel.
On the first one I drilled out I took it right to the point.... I went 1/8". But I also put on a adjustable gas block as well.
Like I said, I have not ever mess around with the 7.62X39 upper, but I spent time on 300 Black Out and once you said the bit went in tight on the non working upper and a had some play on the working, I would about bet you a cold beer if you drill it out it will run fine.
Keep me updated with what you do. JB
Sounds like its making a good seal, but the port is just to small and the gas is getting out the barrel and not the port. If you drill it out, make sure you put a cleaning rod in the barrel first so do do not drill the bottom of the barrel.
On the first one I drilled out I took it right to the point.... I went 1/8". But I also put on a adjustable gas block as well.
Like I said, I have not ever mess around with the 7.62X39 upper, but I spent time on 300 Black Out and once you said the bit went in tight on the non working upper and a had some play on the working, I would about bet you a cold beer if you drill it out it will run fine.
Keep me updated with what you do. JB