Finally dialed in my SBR load

[SwissyJim]

So, I finally got some free time to dial in my 5.56 SBR load. After picking up a number of the bonded 62gr soft points from RMR, I wanted to make a load that was efficient in my 10½" barrel. I did some reading on the intertubes about 'non-standard' powders. I wanted to find one that burned as complete as possible. Cross referencing what I read with Quickload, I narrowed it down to just a couple to try... IMR3031, IMR4198 and Alliant AR-Comp. All burned in the 95-99% range according to QL. Others I tried just for grins and giggles were Varget, CFE223, Benchrest, and H335 but they were no better than 88% complete burn.

I don't have a whizbang setup for testing, but using my Magnetospeed, a front benchrest only and a camera I was able to settle on the IMR4198 as my preferred load. I got the best FPS, and it was accurate, plus it seemed the least smokey with the can on, as told by my 'gas face'. The only issue was unsuppressed, I did not get BHO (it functioned in every other way tho). But, seeing as how my SBR has a dedicated can, and it ran flawless once I attached the can, I'm ok with that.



Never mind the single holes, those were later and unrelated to the testing. The upper group was the 10 round test, while the group on the bullseye was 5 rounds suppressed, all at 50 yards. The chrono info:

Series 6 Shots: 10
Min 2315 Max 2404
Avg 2335 S-D 26.4
ES 89

Series Shot Speed
6 1 2328 ft/s
6 2 2331 ft/s
6 3 2320 ft/s
6 4 2316 ft/s
6 5 2315 ft/s
6 6 2326 ft/s
6 7 2333 ft/s
6 8 2354 ft/s
6 9 2329 ft/s
6 10 2404 ft/s

I had better ES and SD numbers when I measured by hand, but these were from my powder thrower as I wanted to see what 'real world' loading would produce.

My 2nd choice would be the Alliant AR-Comp, it was nearly as good but I rarely see it here whereas I see I4198 constantly. It ran about 100fps slower and the ES/SD numbers were greater, even with hand measured loads. Plus it seemed smokier with the suppressor on - I got more in my face (unscientificlly noted BTW) But a strong 2nd place. I all but eliminated the 3031 as I was getting beat up brass, even with loads that were not near the max... including ejector marks and a serious small dent on the neck/throat of the brass. Non of the others had these issues.

Now I get to start loading the 4k of the bullets I bought