How did you know it was 4" too long? Was it just trial and error? I'm fine with cutting it, but what has me puzzled is my other upper is functioning as it should with same spring.
How did you know it was 4" too long? Was it just trial and error? I'm fine with cutting it, but what has me puzzled is my other upper is functioning as it should with same spring.
If the same lower was used for both uppers and you are only having issues with one of the uppers, then you can put the spring and buffer possibility aside for now.
If you can, find a rubber or plastic tube that fits over the gas tube in the upper and see if you can blow air through it. If you can, then try swapping the gas blocks.
Make certain that the gas ports are aligned between the block and barrel.
Last edited:
Any updates on this?
Probably too busy grinding on parts to post.
To me it sounds like the gas port is to small and needs to be opened up. I ran across this a few times on 300 BLKout. I had to open them up a bit and use a 9mm spring with sub-sonic ammo. Then on some of the 5.56 guns I had to open them up to .093.
This is what I found on the other page with 7.62X39mm::: (This is not from me.)
Few variables like: load you're running, buffer, recoil spring (rifle or carbine)....but a good starting point with something like Tula and a carbine buffer and spring on a mid-length gas system is around 0.095"......some systems end up around 0.100" to 0.114"....
This is what I found on the other page with 7.62X39mm::: (This is not from me.)
Few variables like: load you're running, buffer, recoil spring (rifle or carbine)....but a good starting point with something like Tula and a carbine buffer and spring on a mid-length gas system is around 0.095"......some systems end up around 0.100" to 0.114"....
Sorry it's been a busy week. I don't think I have a flexible tube that will fit over the gas tube, so I'll swap out the gas block and tube with the functioning upper. I'll measure ports on both barrels at that time. I'm hoping to get to the range this weekend. I'll give an update as soon as I try it. Thanks for the help!
How did you know?! There's practically nothing left.
Thanks, I'll measure the ports and see if there's a difference between my 2 uppers!
Coltdogg: How did you get an exact measurement on your gas port? I was switching out the gas blocks and tubes tonight and the gas port on the non-functioning upper is visually smaller. A 5/64" drill bit fits tight in non-functioning upper and same drill bit has play side to side in functioning upper.
The ports look like they had a good seal from block...perfect circle on both ports and didnt look like there was any blow by on either one. So im leaning toward reaming out the smaller port. Do you or anyone else have any thoughts?
The ports look like they had a good seal from block...perfect circle on both ports and didnt look like there was any blow by on either one. So im leaning toward reaming out the smaller port. Do you or anyone else have any thoughts?
Last edited:
