Requesting recommendations: .223 or 5.56 for very short barrel

[CR Williams]

Specifically, a 7.5" barrel with a 1:7 twist. Would like your thoughts on an appropriate round for it. Thank you.

[JHC]

I think the answer is always 5.56 for any martial oriented carbine. If your question meant chambering.

If you meant loads, the ammunition board here has DocGKR's benchmark posts about the best loads, with some nuance about certain applications.

[TheTrevor]

5.56 or .223 Wylde, both of which allow you to run .223 or 5.56 ammo. I like Ballistic Advantage and Rainier Arms barrels for custom-built ARs, and they offer barrels in the lengths you're looking for.

ETA: Or apparently you're looking for ammo recommendations, in which case...

[CR Williams]

Wasn't clear, sorry. I'm losing a lot of velocity with the short barrel, something around 8-900 fps if I understand things correctly. Looking to make sure I have, if possible, specific HPs and/or SPs that will perform best at the reduced velocity.

[TheTrevor]

You have two choices, really:
(1) develop your own custom-load 5.56 recipe optimized for short barrels using heavy projectiles and fast powder, which WILL be time consuming and require great care to avoid dangerous overpressure conditions
(2) switch to 300BLK which is designed/optimized to function well out of short barreled rifles; shooting 300BLK economically also requires hand-loading your own ammo, but you can use proven-safe load data instead of having to develop your own

I've never heard of a commercial load which delivers the kind of velocity you're looking for out of a 7.5-inch barrel.

[TTS]

Hopefully DocGKR can respond...

The 50gr TSX did well out of very short barrels.
http://www.ar15.com/ammo/project/Self_Defense_Ammo_FAQ/DocGKRData/223%20Barrier%20Rounds.htm

[Haraise]

IIRC Black Hills did a run of 55gr TSX for 7.5" barreled guns, some kind of EP contract. Would contact them.

[DocGKR]

.300 BLK 110 gr TTSX is the best option in a 7.5" barrel; otherwise the 5.56 mm BH 50 gr TSX loading.

[CR Williams]

You have two choices, really:
(1) develop your own custom-load 5.56 recipe optimized for short barrels using heavy projectiles and fast powder, which WILL be time consuming and require great care to avoid dangerous overpressure conditions
(2) switch to 300BLK which is designed/optimized to function well out of short barreled rifles; shooting 300BLK economically also requires hand-loading your own ammo, but you can use proven-safe load data instead of having to develop your own

I've never heard of a commercial load which delivers the kind of velocity you're looking for out of a 7.5-inch barrel.

Not trying to get anything specific out of it, TT. I acknowledge that at best I'll probably have about 2100 fps of muzzle velocity, probably between 19-2000, and want to have the commercially-available rounds that still have the best chance of working as they are designed to at the lower velocities. For now, don't want to investigate 300BLK.

Thanks, DocGKR, TTS. I'll see about getting some of that.

[Rich]

I would use the black hills 5.56mm 50gr TSX in any length barrel.

I would love to get rid of my LMT 14.5 carbines in favor of a 9inch barrel 6.8. !

[jstone]

Your best option is going to be something like the 64 grain nosler bonded solid base or one of the lighter tsx bullets. The bsb expands down to 1600fps and a standard tsx is 1800fps.

The 50 grain tsx that blqck hills loads needs 2300 fps to expand due to its robust design. Thats why it is so good at defeating barriers like auto glass.

IIRC DOCGKR also recomends the bsb in the top 3 for barriers like auto glass.

Another good load would probably be the federal tactical bonded. I do not know what the threshold for expansion is, but it should be similar to the bsb.