My son has a Bushmaster AR it has a 24 inch barrel with a 1/9 twist with a free floated barrel. I am having trouble getting heaver bullets to group well. Using the 69 grain Sierra Matchkings it is shooting almost a 5 inch group at 100 yards, this is using Varget. It shoots about the same group using the 55 grain Noslers, and again with Varget. It will shoot a much tighter group using Benchmark and the 55ers. I still think that it should shoot much better. Under an inch at a 100 easily.
I have the same rifle except my rifle has a 1/8 twist and a 20 inch barrel. My rifle shoots 1/4 inch at a 100 using just about any load with Varget and it doesnt shoot the Benchmark very well.
My question is: Is Varget too slow burning for that longer barrel? And any suggestions on a faster burning powder to improve on the group size?
I agree..... however I am not seeing any evidence of that on the brass and its just with the varget powder.... well and the heavier bullets. I dont belive that I have tried to shoot the heavy bullets using the faster powder yet... it shoots the smaller grain bullets MUCH better.... Less than an inch at a 100.... I spent a couple of hours yesterday cleaning it and removing all the copper from the barrel. There was quite a bit so that may help some....
But the difference between the two bullet weights and powder is amazing.... If it is a barrel problem I will be replacing it with a 20" barrel.... I think that the 24 is an overkill.... I had a Bushmaster with a 11.5 inch barrel that would shoot an inch or better... of course we werent using them for anything longer than that.... and that was really a poke.... mostly 25 and under....
Back to the topic tho.... The way it shoots the faster powder better than my 20" got me to thinking... thought I would ask here
I have a DPMS 20" barrel that LOVES the Hornady 75gr. HPBT Superformance Match ammo. It has the same twist as yours. I will say this too; I have a 260 DPMS that came with so much fouling I didn't think I was EVER going to get it clean! Copper and all. I even called the dealer who swore it was straight from the factory so I wrote them. Their reply was that they shot it "a few times more than ten" and simply ran a bore snake through it. Once I got it clean, it has stayed clean and shoots terrific. I think once you get yours clean it should do better. Did not have that issue with the 223.
Also, have you been chronographing the loads? A chrono will tell you a wealth of info about your loads. I can't understand why a four inch difference would be a detriment to accuracy and DPMS barrels are normally fine so I am suspecting the loads, not so much the powder but the velocities. Five inch groups says something isn't right with the speed. That's the easiest part of the puzzle to put in place. If that ain't it, I don't know but I'd think about having DPMS look at it. Work with a chrono, it's an important tool in reloading.
I really didn't want to go there first; but rdsii64 may just have the right answer. I still think I'd give the rifle the benefit of the doubt and work on cleaning and chronographing loads b4 sending it back.
If you want to continue working with it, I'll offer up this load for you to consider. I have shot this load in 4 different AR's with barrels from 14.5, 16 and 24 and 2 bolt guns. Everyone of them shot into 1/2 inch or less.
I used new or once fired LC brass, 25.3g of AR Comp powder and the 52g SMK or 52g AMax or 53g VMax. If you want a heavier bullet the Hornady 75g HPBT with 22.5g AR Comp. I used the CCI 400 and 450, the Remington 7 1/2 BR, and the WSR primers. It didn't seem to matter which one I used. I don't believe this is a top end load but it's been very accurate for me.