Re: MP modified 311410. Anyone getting acceptable accuracy 300blk?

[L1A1Rocker]

I'm looking to load this supersonic in my 300blk (7.5" barrel AR) but have not read of any stellar success in accuracy. Does anyone have any good info on this bullet?

[BK7saum]

I am guessing that you have a gas checked mold. I have only loaded this subsonic with the deep hollowpoint bullets. I shoot a bolt action Rem 700 and Howa Mini.

I would try to load a medium to hard bullet, say 12-16 bhn if you are looking for top end loads. Even then the 1 in 7 or 1 in 8 twist may limit you to 1700-1800fps. I hope you can go higher, but wouldn't be surprised if that is where you end up.

[Gamsek]

I was in 2018 mostly using MP 311-410 at 1150 fps. No matter what alloy I used, with GC (alu or copper) I got similar accuracy. I did found that going from
.3095” to .311” dia shrink my groups for 50%.

That was 10 shoots each circle, at 55yards.

[Burnt Fingers]

I bought the plain base mold.

In my 7.5" upper I can't get plain base cast boolits to group. At 25 yards I'm lucky to keep them on a 12"x12" target.

I've tried a couple of gas check designs. I can almost get them to group. I'll get four in a group then a flyer that's way out there.

I'm suspecting my barrel just doesn't like cast boolits. I have everything to build a 10.5" upper. I'm just waiting for it to cool down a bit. Then I'll get back to testing. The 7.5" will shoot jacketed and plated bullets just fine.

I recently bought the same mold in a gas check version. I have yet to cast any. But I will test both. I'm really hoping I can get a plain base cast boolit to shoot in the new upper.

I was going to go with a custom barrel with a slower twist. I haven't gone that far yet. I found a deal on a 10.5" barrel with a 1:8" twist.

I've found that getting a 300 Blackout AR to both function and group with plain base cast boolits doesn't happen often.

[popper]

10.5" 1:8 pistol, 170gr PB & 185gr GC @ 50. 145 GC or PB go faster. Eject 3 oclock about 5 ft. Oh, bottom group is 185 but only one with a GC. Barrel is 'economy' KAK. Can't get good groups from the pistol @ 100 but the carbine does fine, pushing 145gr PB MOA @ 100, ~2k fps. Got a GC 145 mould that does as good, push a bit faster. Relegated the 145PB to the pistol with cfepistol powder. Got some kids planning a shoot Thanksgiving and this will be reduced load.

[sutherpride59]

I haven’t loaded them in a while but I remember getting 3” groups at a 100 yards gas checked and lubed with a version of bens red, over 16 grains of H110 with CCi small rifle. My brass is my own converted and if I can’t remember how far I seated them. Accuracy was ok. 300 just isn’t a tack driver with cast, it could be with expensive copper stuff but if I need a tack driver it would be in .308 anyway.