Need help with a Supersonic 180gr load with IMR4198

[BigV316]

Hi all, I'm looking at the load data on the Hodgdon site and noticed load data for 16 inch 300 blk, 180gr SP, 15.9 gr of IMR4198. When I filled the case the powder was up almost to the base of the neck. The load data says this should get about 1500 FPS.

Will this load be safe in a short barreled AR pistol (7.5in)?

[dellet]

If it’s safe in a 16”, it will also be safe in a 26” or 6”. Barrel length does not determine load safety unless the barrel is so long the bullet stalls and sticks, or so short that it catches something on fire. I’m guessing your combination will probably have a nice fire ball out the end of the barrel, but should not create any unsafe pressures.

Speer, Sierra and Accurate all have data online for 180 grain supers. Might be worth a look. Most loads will be compressed at the high end if not a starting.

[BigV316]

The subsonic load data for the grain bullet is 12gr of imr 4198. If I started there and worked what would be the increment?

[dellet]

I guess that expends on what you’re are trying to accomplish. If you want a super load, I would not waste the time and materials working up from the very bottom. If I did it would be no less than 1/2 until I got to 15 just watching for pressure, then .2 grains until I reached max load, then back off to the best accuracy.