Cast lead 300 Blackout in a short barrel?

[am44mag]

I'm planning on building a 300 Blackout "pistol" that will eventually be converted to a rifle once all the ATF stuff is finished up. It's either going to have a 7.5" or an 8.5" barrel, and I plan on using the LEE C312-155-2R for standard loads, and either the LEE C309-200-R or the LEE TL309-230-5R for subsonic loads. They will most likely be PCed.

My question is, is the gun going to have reliability issues with such a short barrel and cast boolits?

[Grmps]

AR 300 Blackout "pistol"
LEE C312-155-2R works great over H110
both the TL309-230-5R and 311-232-FN work good over 700X for single shot shooting

[Moonie]

Assuming this is an AR pistol build a barrel that short might have some issues cycling due to the short dwell time. We have a 10.5" AR SBR that started off life as a pistol. Functions perfectly. The shorter the dwell time the more issues you can have with it.

[osteodoc08]

Use 296 and you’ll be fine. One of the benefits of the 300 BLK is near complete powder burn in 8” or so.

I’m getting 2200fps out of my 8.5” barrel with 110gr Vmax and 296.

[Dirtjumper895]

I used ~ 11 grains of A1680 to cycle my 8.3" 300 BLK and keep the rounds subsonic with the 230gr Lee TL boolit.

[Wedgie]

I have had good operation and accuracy with 7.7 gr of 4227 behind a 247 gr NOE.

Makes about 770 fps out of my 8" suppressed.

That was as slow as I could go and reliably run the action.

[2wheelDuke]

At worst you may have to open the gas port and get an adjustable gas block. You might also need to adjust the buffer weight. After some tuning I'm sure you'll be good to go.

[am44mag]

That's good to hear. I think I've decided on the 8.5" barrel. I've also got plenty of H110 to play around with, and I'll get a few more powders to try with the 230gr Lee.

I think this is going to turn out to be a pretty fun gun. Thanks fellas. :D

[asmith80]

You shouldn't have any cycling problems with H110, especially with a pistol length gas system. The only issues I've come across with my 300 Blk and cast bullets is that I'm finding I really have to give the magazine a good smack to seat it completely if I'm trying to insert it with a closed bolt. Something about the way the .223/5.56 mags are designed on the inside and the slightly larger dimensions of the cast boolit I'm using (Lee 312-155). No feeding issues, but if the bolt's not picking up the next round that's the problem. I try to put a fresh mag in with an open bolt now, and don't worry about it