I seem to recall that 11.5" is about as short as one can go for M193-type ammo to fragment.  That's probably the main reason I have resisted the AR pistol urge so far.

What defensive 5.56 ammo are you using for your AR pistols, say =<9"?  I would appreciate any studies or tests that support your choice.

Conventional wisdom that usually gets settled on among ARFCOMers, as derived from studies by government organizations (mainly Crane, as far as I'm aware), is that the terminal ballistics of pretty much all 5.56 ammo goes to shit once you bring the barrel under ten inches. I'm not sure exactly what sort of math they used to arrive at that conclusion, but that's why they settled on 10.3" for the barrel on the Mk18.

Regular FMJ bullets, like what's in M193, rely on fragmenting for their terminal ballistics, which relies heavily on high impact velocity to successfully achieve. Bullets designed to mushroom for their terminal ballistics, like softpoints, will usually be able to successfully mushroom at lower velocities than what you need to get FMJs to fragment. Their terminal effects normally aren't quite as devastating as fragmenting bullets that are going fast enough to successfully fragment. But if you already plan on using a barrel short enough that it probably won't be able to achieve fragmentation velocity, a softpoint that successfully expands will be better than an FMJ that fails to fragment.

This is just my opinion, but if you haven't already bought an upper yet, I wouldn't buy anything shorter than 10.5". If you already own an upper that's 9" or shorter and need to make it work, buy softpoints in a heavy grain. Either way, get some sort of softpoint. Speer Gold Dots in 62gr or 75gr are both great rounds.

Fusion or gold dot

Here's a couple of videos you might like. The first one is IMI 77gr Razor Core from a 10.5" barrel. This is what I use.

https://youtu.be/pzicw0Q8HRg

This one is is BH Optimized 50gr TSX from a 10.5" barrel.

https://youtu.be/5o-Tw0BbLd0

What is the hive's opinion on Hornady Black 75gr. interlock HD SBR?

10.5" here, I use IMI 77gr for HD. I get the would cavities I want and I don't have to worry too much of bullet liability once it hits exterior walls.

IMHO, any modern SD cartridge will work. I want a bullet designed to mushroom consistently with proper velocity. I don't want to rely on a variable like yaw. Others I would trust are 64 gold dots, 75gr gold dots, 75gr T2 TAP, 64gr Fusion, CBC 77gr, MK262, MK318. There are more, but you get the idea, modern bullets.

Shorter than 10" you start losing a lot of velocity. To keep the velocity in the proper expansion range, 64 gold dots, 64gr Fusion or 50gr TSX would be better choices. Even with those, a very short barrel, 7-8", might not give you the velocity needed to get proper expansion or not very far.

That's what I have in my SBR w/ suppressor.

Very well put.

I keep two magazines of IMI 77gr handy (don't have any children to worry about) and two more with 62gr TSX in the safe for Soviet zombie invasion purposes. I figure, if I'm ever in a situation where I've exhausted 60rds of MK262 in continuous contact, the reality is I'm cooked. So I'll accept that .000000001% risk.

I like the performance out of my 10.3" with 75 Gr. TAP

Consider 300 blk...

75 go TAP/ Gold Dots / Privi 75 grain are what I have. Can not afford BH stockpile

Thank you, all.

I think DocGKR needs to do some more testing with short barrels.

I think I've settled on Hornady SBR and / or Gold Dot 75. Testing groups, feeding currently.

Just curious, what do you all think of the FBI load our of a 10.3 / 1:7 Geissele. Bone Frog has em in

Here is a video from ARFCOM on the FBIT3 load from a 10.5" barrel:


I have 500 rounds of this stuff for my HD SBR (barrier blind load)

Fusion expands down to 1700fps:

https://www.youtube.com/watch?v=otou1Fws4cQ

Most any SD oriented bullet will be devastating at any realistic range from any reasonable (>10”) barrel. People will debate endlessly about which is best and why, but in the real world these debates are mostly academic. I like TMK and Gold Dots. Pick a winner (Barnes, TMK’s, 77/75gr OTM’s, PDX, Fusions/Gold Dots, whatever), and spend money and time practicing.

well said.

Any modern SD load will work.