Okay, first off, I am not sure how to word the question in order to search for it.
I have never seen this before in any firearm, however, it is my first time trying to change a caliber in a semi-auto.
I finally shot the barrel out of my DPMS LR-308 and while I was looking for a replacement, I came across a 6.5 CM in 24" which is longer than my original 16" .308 barrel.
It is rifle length porting, so I replace the gas tube, reused the rest of the parts including the gas block. Now, I am pretty sure the thing is over gassed as it blows primers in some factory ammo. Winchester Match specifically, although I was told that there is an issue with the Winchester Match LRP ammo so it could be an ammo issue. I don't see this in other manufactures' ammo. I decided to load a ladder to see what it likes and found something interesting. First, it blows brass 10-12 feet away, again I know it is over gassed. What surprised me is the muzzle velocities. It is fixed at 1450 fps, give or take 10 fps. Does not matter the load, or the manufacturer is always around 1450 which is miles below 2700 the same loads get in my bolt guns with the same barrel length.
Now I expect to see some velocity drop, it is ported, after all, I don't think 1300 fps is reasonable, however. I can come up with three things, first, the powder is to slow and does not burn anywhere near fast enough for the rifle length barrel and it is venting through the port. This means a faster powder might work (I am using H4350 which all my bolt guns love) but I can't help but think that the gas block is also an issue. Has anyone else seen this? Should I go for an adjustable gas block? I plan to put a can on this anyway for varmint hunting.
I have never seen this before in any firearm, however, it is my first time trying to change a caliber in a semi-auto.
I finally shot the barrel out of my DPMS LR-308 and while I was looking for a replacement, I came across a 6.5 CM in 24" which is longer than my original 16" .308 barrel.
It is rifle length porting, so I replace the gas tube, reused the rest of the parts including the gas block. Now, I am pretty sure the thing is over gassed as it blows primers in some factory ammo. Winchester Match specifically, although I was told that there is an issue with the Winchester Match LRP ammo so it could be an ammo issue. I don't see this in other manufactures' ammo. I decided to load a ladder to see what it likes and found something interesting. First, it blows brass 10-12 feet away, again I know it is over gassed. What surprised me is the muzzle velocities. It is fixed at 1450 fps, give or take 10 fps. Does not matter the load, or the manufacturer is always around 1450 which is miles below 2700 the same loads get in my bolt guns with the same barrel length.
Now I expect to see some velocity drop, it is ported, after all, I don't think 1300 fps is reasonable, however. I can come up with three things, first, the powder is to slow and does not burn anywhere near fast enough for the rifle length barrel and it is venting through the port. This means a faster powder might work (I am using H4350 which all my bolt guns love) but I can't help but think that the gas block is also an issue. Has anyone else seen this? Should I go for an adjustable gas block? I plan to put a can on this anyway for varmint hunting.
