Supersonic/Subsonic 300blk in same gun?

[basykes]

Hello all, I'm building a 9" 300blk Ar pistol and I'm curious to hear what yall thank. Can the same gun easily shoot both subsonic and supersonic 300BLK rounds? Can I just switch out mags one with subs and one with supers? I have heard both ways, some say that its works fine others say that it wont. The upper and BCG is all coming from BCM. Let me know what yall think, thanks.

[themonk]

A properly done gun should shoot all 4 ways - 300 was designed to shoot unsuppressed supers, unsuppressed subs, suppressed supers, suppressed subs.

ETA - a lot of gun makers and barrel makers are clueless when it comes to 300 blk. They think its just like 556 and don't even look at any of the info AAC put out in 2012.

[opngrnd]

Depends on how the barrel is ported. Some will not cycle subs unsuppressed.

[Clint]

The BCM 9" should be good to go with a CAR buffer for subs and an H3 buffer for supers.

Doing mixed subs/supers in 300BLK pistols is similar to doing mixed suppressed in 556.

The barrel has a gas port size in between the 2 ideal gas port sizes.

It will be slightly under gassed one way and slightly over gassed the other.

Using a light buffer and then a heavy buffer mostly compensates for it and produces good overall function.

[tb-av]

In your case I would ask BCM.

The answer to your generic question is yes it can be done.

I do it with an adjustable gas block. Others do it with gas port sizing.

I wanted an adjustable so you could turn it into the most quiet single shot by cutting the gas off if desired. I am sure though that I could set my gas to a central range and shoot either. In fact that's what I do, but things start to get dirty and dry pretty fast and then the subs will fail to cycle. So for me then it's lube or more gas. I don't do a lot of back and forth but I have done it. Basically to learn what it will and will not do and what goes wrong when type of deal.

In general, clean lubed gun, I would say yes to most. Unless they specifically tell you it's made to run one way or the other.

I'm a data point of one though so take with grain of salt. SOLGW barrel / SLR gas block. Rifle configuration ( pistol gas length ) with standard BCG and Vltor A5 receiver situation.

[tb-av]

double - delete

[CPM]

I have a $250 8.5” PSA nitride 300blk upper that runs anything and everything suppressed and unsuppressed. Pistol gas, carbine buffer. It also shoots a ragged hole at 100 yards. I bought it on a whim just to see if I liked the round and it has worked so flawlessly I have not felt the need to “upgrade” to something different. It tickles me to death every time I shoot it.

[rjacobs]

If you need to do all that monkeying with buffers, the gas port is not right.

My AAC 9" runs subs, supers, suppressed, unsupressed with an H2 buffer and carbine spring. Thats how AAC spec'd it to run. H2 with carbine spring in the 9" guns and C buffer with carbine spring in the 16" guns.

Ive been surprised by what all my gun will cycle.

[boss_hawg]

My 8.5” setup cycles all four ways but the problem that I’ve found is the optic.

You need four different zeroes which is complex even with the dopes.

I generally will run 100% suppressed zeroed for supers and Kentucky windage the drop off with subs.

[opngrnd]

My BA doesn't run subs unsuppressed. Honestly not too happy with it, but I like everything else about it enough I haven't pulled the barrel yet. Some days I get pretty close to pulling the barrel, slapping a 5.56 barrel on, and getting back to it, but there's just something about the set up I like that makes me want to buy a 30cal can and drive on. If LMT enhanced carriers were more plentiful, I wonder one would be enough to get it running unsuppressed.