Lee 312-155 for 300 blackout

[emorris]

Howdy all. I recently completed my blackout build and I'm looking for a little guidance for my cast loads. I'm using the lee two cavity 312-155 mold gas checked and sized to .310. Lube is Carnuba red and brass is formed LC 223 brass. 16 inch barrel with carbine length gas port. I have search the net far and wide for the last three days to get an Idea of where to start. I started with Lilgun and worked up the load from 15.5 grains to 16.8 grains. The bolt did not lock back until I reached 16.8 grains. There were no over pressure signs, but I'm afraid to push this load any harder, since I cannot find any reference material that shows what a max load is with a cast boolit of the same or similar weight. I also picked up a pound of accurate 1680 to try next. I have been all over 300 blk talk, but most are using jacketed bullets. I can understand not wanting to post load data, but it would be really helpful if someone can point me in the right direction to look. Thanks for any help.

[blikseme300]

There are a number of posts about this boolit in the 300blk on this forum as well as the 300blk forum BTW. My personal favorite load is 17gn of Reloder 7. Clean burning and very good accuracy out to 100 yards. I have used a number of other powders including Lil Gun with so-so results. My 2 AR-15 type 300blk rifles are both 16" carbine gas systems and functioning and accuracy matches factory loads. These loads have also been run through a 8" SBR with can with factory matching accuracy and functioning.

[Mike Hughes]

17 gr of reloader 7 with the Lee 312-155 is also my favorite

[wool1]

If you substitute a cast bullet for a jacketed of the same weight, you should get higher speed, less pressure. Seems to work out to about a 10% trade off. Just my experience...ymmv

[Moonie]

I like 15.3gr of H110/W296 with this boolit in our 2 uppers. Haven't played with RL7 yet but planning to for subs as I don't have access to AA1680.

[Jupiter7]

Howdy all. I recently completed my blackout build and I'm looking for a little guidance for my cast loads. I'm using the lee two cavity 312-155 mold gas checked and sized to .310. Lube is Carnuba red and brass is formed LC 223 brass. 16 inch barrel with carbine length gas port. I have search the net far and wide for the last three days to get an Idea of where to start. I started with Lilgun and worked up the load from 15.5 grains to 16.8 grains. The
bolt did not lock back until I reached 16.8 grains. There were no over pressure signs, but I'm afraid to push this load any harder, since I cannot find any reference material that shows what a max load is with a cast boolit of the same or similar weight. I also picked up a pound of accurate 1680 to try next. I have been all over 300 blk talk, but most are using jacketed bullets. I can
understand not wanting to post load data, but it would be really helpful if someone can point me in the right direction to look. Thanks for any help.

Stop, 16.8grs lil gun is up there. Mine function at 14grs and up, I run them at 15.5-16grs with mild overpressure signs at 16grs. There is something else amiss. Check gas port size and gas block alignment. Opening up the gas port to .100 to .125 will help functioning tremendously.

[sly mantis]

Anyone tried imr4198 with 300blk? Ive got a fair bit of it.
Im in the process of building a 8" SBR AR15 unsuppressed (im in Canada so no suppressors here) with the 155gr lee mold. Not going for subsonic. Any recommended load data for other powders is also appreciated.

Thanks

[Jumbopanda]

How of hard of an alloy do you guys use for 300blk?

I've heard many people say that they get good results with the proper supersonic load, but it seems to be that it's really easy to exceed the recommended RPM rate for cast boolits in 300blk due to the fast twist. Even a modest 1400 fps gets the boolit spinning at 144,000 RPM out of a 1/7 barrel.

I'm just starting out as well, and last time at the range I fired off some loads of a 140gr boolit (GC'd, wheel weights, not heat-treated). My 16.5gr of Lil Gun got it going 1900fps, which was quite a surprise. Needless to say, lead got shaved, squirted, and splattered everywhere and accuracy was beyond terrible.

[Jailer]

Air cooled wheel weights or a similar alloy is fine for what you are trying to do. Back it down to around 15gr of H110 and try again. H110 gives me my best accuracy with cast but I seem to be in the minority with that.

[runfiverun]

rpm rate :lol: :lol:
it's static fit that is killing you.

[Jumbopanda]

I think I'm going to work on subs or low velocity supersonics for the time being. I did manage to get about 1.5 MOA with a 200gr subsonic load today. That was by far the best one; most others grouped about 3-4 MOA but that's still a big improvement over the 8-10 I was getting last time. I can't really complain too much about 3 MOA for a cheap plinking load either.

Oops, sorry for the thread hijack!