shot my new AR15 upper with an adjustable gas block over the chrono this afternoon. was fairly surprised with the results.
i'm shooting some cheap reloads that are reasonably accurate but have never had a great SD. so i shot them today, 40 degrees, and got a mean velocity of 2889 and standard deviation of 43 fps. this was for 15 rnds, so it's a fairly reasonable sample size... not like i just shot 3 rounds or something.
then i shut off the gas completely so that the bolt didn't cycle at all and got the following: 2869 mean and 15 SD.
that makes absolutely no sense to me. i would have guessed turning off the gas might have added a few fps, not drop 20. and it seems the only way the SD would improve so much would be if the gas system itself were responsible for quite a bit of deviation. that seems improbable.
anyone ever tested this before. any ideas?
i'm shooting some cheap reloads that are reasonably accurate but have never had a great SD. so i shot them today, 40 degrees, and got a mean velocity of 2889 and standard deviation of 43 fps. this was for 15 rnds, so it's a fairly reasonable sample size... not like i just shot 3 rounds or something.
then i shut off the gas completely so that the bolt didn't cycle at all and got the following: 2869 mean and 15 SD.
that makes absolutely no sense to me. i would have guessed turning off the gas might have added a few fps, not drop 20. and it seems the only way the SD would improve so much would be if the gas system itself were responsible for quite a bit of deviation. that seems improbable.
anyone ever tested this before. any ideas?