First go with the 300 BLK

[Pistolero]

Just a bit of experience - but with J-bullets in .300 BLK. I had best results with H110 at just
under 10 gr. 10 gr popped supersonic too often. 1680 didn't impress at all after being told
"you HAVE TO use 1680 or the AR won't run". Mine runs perfectly with H110, or 2400.
1680 seemed to give trouble running if lowered to subsonic. Go figure.

Since this cartridge seems to have a LOT in common with the .30 Carbine, it would seem
that a powder created for .30 Carbine (H110) should be perfect. IME, with 220 Sierra
JHPs, it is.
Have not wanted to crud up my non-disassembleable can with normal lubes, so staying with
Jbullets so far. Considering commercial powder coated cast as an experiment - not really interested
in getting into P-coating.

Bill

 

[300BLK]

In my carbine length gas, I prefer H110 and IMR4227, but only shoot supers and no suppressor.

My next upper will be with pistol length gas and an adjustable gas block. That combo should allow faster powders like Blue Dot and 2400 to work with a wider window of function.

 

[Ian]

"you HAVE TO use 1680 or the AR won't run".

I had to wade through the same line of tripe. Fortunately, friend nearby loaned me some to try and his new bottle was returned promptly with very little missing. At low pressure AA1680 is extremely erratic and very inaccurate IME.

If you have a PISTOL LENGTH gas system, or are only interested in building loads well up into the supersonic range, your options expand greatly. If you're running a carbine gas system and want to run subsonic, without a suppressor, your options become 220 grains or more (with cast) and powders that will work narrow to three: Some flavor of 1680, 4198 (only IMR on that one, BTW), and Reloder 7, with Reloder 7 being the ringer by a wide margin. BR-30 and 32 might work, maybe, but I haven't tried them.

 

[300BLK]

One of my cohorts LOVES 1680, but he's shooting 190gr supers. I don't feel the need for heavier than 170gr bullets, and have gone in the opposite direction to find a soft recoiling load. Going in that direction I discovered that 4227 and Reloader 7 both burned pretty cleanly at pretty mild pressures.