So I tested my first batch of reloads (first shots ever in my new 450 Bushmaster AR) this past weekend. All in all the gun ran well. The only functional issue I had were a few failures to feed from one magazine. Otherwise all my loads cycled the gun with no jams or failures to eject.
Glad I brought the sissy pad for the butt stock. I have waffle tread bruise on my should from A2 butt stock and the first fifteen rounds. Then I wimped out and put the pad on. My shoulder thanked me. The recoil was not horrible and for hunting with hunting clothing on I think it would have been fine but shooting over a bench with only a T-shirt on and that A2 butt stock the recoil got to me eventually.
Weather was about 75F and humid, with overcast sky. My chrono is an old Chrony Alpha Master set about 12 feet in front of the muzzle. My target was set just 45 yards down range. Once I have a load or two I am happy with I will setup for some longer ranges. I plan on zeroing it at 100 or 150 yards for hunting.
I had three bullets each with three incrementally higher powder charges. I weight every charge on my scale after it dropped and trickled to met the load.
First was 230gr FMJ (Armscor)
Pushed by Lil'gun and lit by WSR primers OAL 2.065
These are 5 shot averages except as noted
33gr Avg: 2120fps ES: 165.7 SD: 64.98
35gr Avg: 2186fps ES: 150.5 SD: 86.04 (3-shots)
37gr Avg: 2294fps ES: 102.8 SD: 41.96
That was about what I expected velocity wise maybe even a touch faster than expected from my QuickLoad workup but the extreme spread and standard deviation was pretty bad. The 33gr group is missing as it was used to bring the new scope reasonably close to point of aim.
Second was 240gr XTP/MAG Hornady OAL 2.060
Pushed by Lil'gun and lit by WSR primers
These are 5 shot averages except as noted
32gr Avg: 2132fps ES: 30.99 SD: 12.36
34gr Avg: 2203fps ES: 30.12 SD: 13.11
36gr Avg: 2297fps ES: 147.7 SD: 63.77 (4-shots)
So the first two charges were what I would expect for extreme spread and standard deviation what happen on the last one? You can even see the group size open up on that one. The flier in the 34gr group was totally on me I flinched on the last shot of the group.
And finally was 300gr XTP/MAG Hornady
Pushed by H110 and lit by WSR primers OAL 2.065
These are 5 shot averages except as noted
30gr Avg: 1653fps ES: 87.73 SD: 34.59
32gr Avg: 1739fps ES: 106.2 SD: 44.08
34gr fat-fingered the chrono and lost the data but this charge shot one of the best groups.
Surprisingly this load was a bit more comfortable to shoot even with the last load that I expect should have been right at or just above 1800fps with that big heavy 300gr bullet. More push than the sharpness of the lighter bullets.
That was a lot of rambling and pictures. My big question, assuming you got this far, is what can I do to tighten up my velocity spread? I would like to see that extreme spread well under 50 fps if I can. First thing that comes to my mind is I did not crimp enough. I used a relatively light crimp on these first loads since 450BM headspaces of the mouth. I may have overdone(underdone?) that. My crimp was roughly .476 but I was afraid to crimp too heavily especially with the cannelure on the XTP. What other things could be causing such large velocity spread? Thanks!