Returned yesterday from a frustrating day on the range trying to zero a Bushmaster AR-15 with 16" barrel. I just got into reloading, and can normally fire consistant dimed sized groups out of my Remington 700 with a 52 gn HPBT round on 25.5 gn of Hodgen Varget. So I figured WTH why not try the same powder weight on a 55 gn Speer Spitz-SP set at 2.175 COL as the good Speer book says...
Well the result was spectacular and not in the good sense. First four rounds 7" low and then one corrected up 2.5" at 25m...
Second group of corrections brings the rounds centered on point of aim at 25m...
Third group, time to switch to 100m and shots all over the place, but primarily low...
Fourth group back to 25m and shots progressively walk downwards as the barrel heats up or fouls from 6" to 16" low and 3" right. (Must note that I'm firing one round about every 30 seconds.)
Fifth group at 25m clearly shows point of impact 5" to 12" below the POA and descends again as the barrel heats up. However closer inspection shows that as the bullets are walking down that they are progressively tumbling or coning. First two good, third 25% profile, fourth 50% profile, and fifth through seventh completely sideways, Eighth through tenth off the target.
(Normally I shoot five round groups, but by now this time I just wanted to blow off the rounds and relieve some frustration. 
So back at home I realize I have a problem... My inclination is to first clean the barrel really well again (it was freshly cleaned before this session). My second is to increase the powder weight by half grain increments up to 27 gn. The third is to try a heavier bullet weight, and the fourth is to try a different powder. While researching this I found some negative comments about fouling with Varget, but I cannot confirm this is the fault.
Has anyone else found this problem or have any suggestions?
I kept the target, due to sheer curiosity and tried to attach the photo but it wouldn't work. I can send it to anyone with ideas.
Well the result was spectacular and not in the good sense. First four rounds 7" low and then one corrected up 2.5" at 25m...
Second group of corrections brings the rounds centered on point of aim at 25m...
Third group, time to switch to 100m and shots all over the place, but primarily low...
Fourth group back to 25m and shots progressively walk downwards as the barrel heats up or fouls from 6" to 16" low and 3" right. (Must note that I'm firing one round about every 30 seconds.)
Fifth group at 25m clearly shows point of impact 5" to 12" below the POA and descends again as the barrel heats up. However closer inspection shows that as the bullets are walking down that they are progressively tumbling or coning. First two good, third 25% profile, fourth 50% profile, and fifth through seventh completely sideways, Eighth through tenth off the target.
(Normally I shoot five round groups, but by now this time I just wanted to blow off the rounds and relieve some frustration. So back at home I realize I have a problem... My inclination is to first clean the barrel really well again (it was freshly cleaned before this session). My second is to increase the powder weight by half grain increments up to 27 gn. The third is to try a heavier bullet weight, and the fourth is to try a different powder. While researching this I found some negative comments about fouling with Varget, but I cannot confirm this is the fault.
Has anyone else found this problem or have any suggestions?
I kept the target, due to sheer curiosity and tried to attach the photo but it wouldn't work. I can send it to anyone with ideas.
