So here is my issue... I built an AR10 (DPMS style) in .308 with a Criterion 18" rifle length gas system, standard weight rifle buffer and spring, and a Toolcraft BCG; this setup runs flawlessly with pretty much all my loadings and with the factory ammunition that I've (sparingly) used.
I decided that I wanted to build another upper in 6.5 Creedmoor. I am using a Ballistic Advantage 22" Premium barrel (rifle length gas) Superflous Arms adjustable gas block, and a Toolcraft HP BCG. Since assembling this upper, and during load development I have had continued issues with cycling. The problem appears to be short cycling.
When I developed a load for this upper I began using SMK 142gr bullets with H4350 powder at 39 grains and worked my way up to 42 grains; I had short stroke issues with the lighter loadings (39.0 and 39.5), but things seemed to be reliable at higher loadings. This was all done with the gas block in the most "open" position. However, I was only testing 5 rounds of each charge weight.
Today I took the upper out to sight it in and initially it seemed to work fine with the load I chose (42 grains of H4350 / SMK 142's); ejection was initially at 3:00. After twenty rounds or so it started to short stroke and the ejection pattern moved to about 4:00. The gas block remained in the most "open" position throughout, I have also verified that the gas port is in alignment with the block.
So, here is what I am wondering about. With the .308 upper the rifle has been super reliable. With the 6.5 upper it has always appeared to be undergassed. Could my issue be the standard .308 rifle buffer and buffer spring? I am temped to change out the buffer spring to a lighter one, but I really don't want to change the parts of the lower; I thought it would be cool to have a large frame gas gun with two uppers in different calibers that could just be push pinned on and things would work...
I could go hotter on my loads, but I am already seeing signs of minor pressure, so I don't think that is the best option. I haven't done a lot of testing with any factory ammo. due to me not having any currently, but I have never had issues with developing functional ammunition across multiple calibers in the past.
Any ideas?
I decided that I wanted to build another upper in 6.5 Creedmoor. I am using a Ballistic Advantage 22" Premium barrel (rifle length gas) Superflous Arms adjustable gas block, and a Toolcraft HP BCG. Since assembling this upper, and during load development I have had continued issues with cycling. The problem appears to be short cycling.
When I developed a load for this upper I began using SMK 142gr bullets with H4350 powder at 39 grains and worked my way up to 42 grains; I had short stroke issues with the lighter loadings (39.0 and 39.5), but things seemed to be reliable at higher loadings. This was all done with the gas block in the most "open" position. However, I was only testing 5 rounds of each charge weight.
Today I took the upper out to sight it in and initially it seemed to work fine with the load I chose (42 grains of H4350 / SMK 142's); ejection was initially at 3:00. After twenty rounds or so it started to short stroke and the ejection pattern moved to about 4:00. The gas block remained in the most "open" position throughout, I have also verified that the gas port is in alignment with the block.
So, here is what I am wondering about. With the .308 upper the rifle has been super reliable. With the 6.5 upper it has always appeared to be undergassed. Could my issue be the standard .308 rifle buffer and buffer spring? I am temped to change out the buffer spring to a lighter one, but I really don't want to change the parts of the lower; I thought it would be cool to have a large frame gas gun with two uppers in different calibers that could just be push pinned on and things would work...
I could go hotter on my loads, but I am already seeing signs of minor pressure, so I don't think that is the best option. I haven't done a lot of testing with any factory ammo. due to me not having any currently, but I have never had issues with developing functional ammunition across multiple calibers in the past.
Any ideas?