300 blackout cast bullet loads for ar-15

[nouseforaname1246]

Ok so im going to be finishing my latest ar-15 build chambered in 300 blackout in the next week or so. 16" 1-8 twist stainless barrel with a carbine length gas system. I got the dies last week and have formed up a few hunded pieces of brass.
I have spent the last 2 days looking for cast bullet load data and havn't come up with much, mostly jacketed data and subsonic cast data.

I dont want subsonic data, I dont plan on buying a supressor in the forseable future. I dont plan on hunting with it, so I dont care about terminal ballistics (which is what every thread ive come across ends up being about.) Im looking for accurate and reliable target loads. I plan to work up my own loads over a chrony, I just want some good starting points and I will post my results for others who are having a hard time finding load data for this cartridge.

Ok so I have 3 bullets at the moment that I want to try; lee 309-170f. Lee 312- 155r. And the lyman 311359. I will probably buy a mould specifically for the blackout, but I would like to try making one of those 3 work. Any suggestions on which mould to buy for my intended purpose would be appreciated.
I have read of people using rx7 and 5744 for subsonic loads, but can they be used for supersonic loads? I ask because I have them on hand and powder is hard to come by right now.

So what are you guys using for your 300 blackout supersonic cast bullet loads?

[Jailer]

Lee 312-155-2R and 15.3gr H110. Runs about 1800 FPS is very accurate and has reliable cycling.

[300blk]

One of my favorites is lee tl 230 5r. sitting atop 11.8 grains of h110. Cycles 8.5 barrel no leading straight lee liquid alox. Fired hundreds. Jailers is very near where i run that boolit. Good luck.

[300blk]

Also due to case capacity the blackout is a hoot to shoot cast in. Fun and much like finding an accurate 9mm load and a lot less like finding an accurate -06 load... If that makes any sense.

[Jupiter7]

Agreed, the 312-155 is the ticket. I run mine sized to .309 seated to crimp with lee FCD over 15.7gr h110.

[nhrifle]

Reloader 7, AA5744 and Lilgun work well with that boolit as well.

[lksmith]

With that setup, using supers, gas checks are a must in my opinion due to the gas system. My best supersonic accuracy has been 17-20gr H110 under a 120-130gr bullet at 23-2400fps, but that was using jacketed since my only mold i have that is suitable for that caliber for using subs

[jarrodl]

One of my favorites is lee tl 230 5r. sitting atop 11.8 grains of h110. Cycles 8.5 barrel no leading straight lee liquid alox. Fired hundreds. Jailers is very near where i run that boolit. Good luck.

Do you crimp? What kind of accuracy do you get? Is it subsonic? if not what velocity?
Thanks

[Moonie]

My favorite load atm is also the .312 Lee 155gr with 15.3gr H110/W296, getting around 1,850 out of my 16" carbine gas.

[nouseforaname1246]

Ok I finally finished my build so im going to go test some loads tomorrow. I loaded up some 170 gr lee fp (I had a bunch already lubed up) over some rx7. Ill let you know how it goes

[Jupiter7]

I'll add my favorite new load for 300bLK. It's a little odd but had to try it out.

Noe clone of ranch dog 311165 standard lube grooves sized .309
Tumble lubed LLA
Aluminum gas check, total weight 169.5grs
COL 1.91
13.5grs lil gun

Isn't the lee 170rf the same design?

This loads feeds from standard GI mags with anti-tilt followers and functions in 10" AR pistol. Also the first rifle boolit I've been pleasantly surprised with accuracy, cloverleafed at 50yds 1st time out. I believe there's room to work up and make this a decent hunting load. If I was OP, I'd use the 5744.

[Moonie]

Ok I finally finished my build so im going to go test some loads tomorrow. I loaded up some 170 gr lee fp (I had a bunch already lubed up) over some rx7. Ill let you know how it goes

I had some trouble with the Lee 170 FP in mine, magazine length issue, they would nose dive in the GI mags I had. Seemed to work better in the magpul mags, but still had issues, they were just too darned short.

[Sur-shot]

I too am interested in the 300 with cast as the supply of jacketed is at least short. I finished my work with the 160gr 6.5 Grendel with a can and now turn my attention to the 300. But in the 300 I have several moulds that I have used for years including the RCBS silhouette bullets and the Lyman .308s and .311 - .312 bullets. I use the .311s in my M-99 Arisaka that I have not shot now for decades. Might have to break that old mould out.

I thought the RCBS 150 FPGC would be a natural for the 300 with H-110, but have yet to try them. I was not aware of the diving problems with the 300, however, I loaded some 125gr Sierra HPs which have a large open mouth and had to shorten them up a good bit so they would feed the last round on the follower, over the mag front. I determined years ago that the AR will function, with some rounds, if you shorten the OAL rather than extend it.
Ed

[Jupiter7]

I had some trouble with the Lee 170 FP in mine, magazine length issue, they would nose dive in the GI mags I had. Seemed to work better in the magpul mags, but still had issues, they were just too darned short.

What was cartridge length?

The trick is making the magazine think it's feeding .223. Otherwise mimicking the neck of .223 with nose of bullet. I'm loading this bullet with top drive band out of case neck. Rib of magazine is hitting bullet about 1/3 from top of nose.

[nouseforaname1246]

Ok so I had some intersting results. I worked it up from 13 gr up to 16 gr. Everything under 14.5 gr wouldnt cycle the bolt. At 15 and it would cycle but wouldnt lock back on the last round. 16gr was cycling perfectly and I had groups around 1.5 inches at 100. (2 five shot groups)
I had no leading at all so far, so im going to work up a few more grains to see if I can shrink that group down some.
I did have problems with the mags feeding properly. They kept nose diving in the mags. I was using gi mags and the bullets were seated so the last lube groove was just barely covered by the neck. I think im going to try my pmags and try seating them longer as well.

[nouseforaname1246]

Ok so I tried several more loads with the 170 fp using different oals and even tried using lil gun. Couldnt quite get them to feed reliably enough. Im pretty sure its the magazines causing the problem so I ordered some anti tilt followers. So in the mean time I finally had time to cast up the 155 gr 312 lees. Loaded those up with 16 gr of rx7 and all 15 of the test rounds fired and fed beautifully. And they held a fairly tight group. So I loaded up a half dozen or so different loads using rx7 and lilgun. Going to fire those off today during my lunchbreak hopefully.

[fredj338]

Are you using gas checks w/ the Lee 155? I am wanting to do a 300 upper & want it just for shooting lead bullets but would rather not gc for say 1500-1600fps.

[Overton-AR]

Well I am just now getting into casting. It is about 90% due
to the new fun 300BLK SBR that I am playing with. I went
with the Accurate mold Bullet design #31-240E. It was designed
specifically to keep the lube rings ABOVE the powder.

I am going to try it with straight linotype and a 50/50 mix
of wheel weight and linotype.

[338RemUltraMag]

Are you using gas checks w/ the Lee 155? I am wanting to do a 300 upper & want it just for shooting lead bullets but would rather not gc for say 1500-1600fps.

At 15-1600 you will need gas checks for a 30 cal.

[fredj338]

At 15-1600 you will need gas checks for a 30 cal.

Thanks 338, I was hoping I could run it like my 45-70, I just hate fussing w/ gc.