I have a DPMS SASS with an 18 inch barrel and 1 in 10 twist. I have always noted with factory ammo that my first cold bore shot of the day consistently went 2 inches high. Fast forward to today when I took my first batch....EVER of handloads to the range. I started with 42.5 grains of Varget with Sierra MK 168 grain bullets, Winchester Brass and CCI BR-2 primers. Had set up my new chronograph and put a round downrange. Sure enough it was 2 inches high. Checked the chrony and it read 2932.6 fps. I bout crapped! I checked the brass and there was no flattened primer nor extractor swipe. Brass looked fine. I fired the second round and it was 2818.3. The velocity continued to fall over the next 3 shots. The following 5 shot string averaged 2520 fps which I would think is reasonable. What gives with the rifle. And before you say I made a mistake and loaded the first round hot I didn't. Because I have an intense fear of a facial amputation I had a senior reloader literally watch over my shoulder for every round I reloaded, just to make dang sure I was doing it right. I think that given the history of each cold bore shot going high this has always happened, I just didn't know because I didn't have a chrony. So the question is what is causing this and second, is it dangerous despite no signs of overpressure.
Here's another toughy. I loaded rounds all the way up to 45 grains in 0.2 grain increments. At 44.2 grains I began to notice negligible velocity increases with increased powder. My question regarding this is where is the extra energy going? Is it that at 44.2 grains I've reached the maximum obtainable burn out of an 18 inch barrel and the rest is simple going out the end of the barrel or is the gas block acting like a high pressure release valve and venting everything over this pressure back into the recoil system? Or maybe a little of both.
Here's another toughy. I loaded rounds all the way up to 45 grains in 0.2 grain increments. At 44.2 grains I began to notice negligible velocity increases with increased powder. My question regarding this is where is the extra energy going? Is it that at 44.2 grains I've reached the maximum obtainable burn out of an 18 inch barrel and the rest is simple going out the end of the barrel or is the gas block acting like a high pressure release valve and venting everything over this pressure back into the recoil system? Or maybe a little of both.
