Does anyone need a 3 inch 9mm AR barrel for an SBR?

[Big Frank]

Does anyone need, or want, a 3 inch 9mm barrel to build a SBR or AR pistol? SOT MFG makes this one. I don't know if the chamber starts at the breech, or if it's like a regular AR barrel with the chamber in front of the barrel extension, in which case it would be a 2 1/2 inch barrel. Someone with a pistol caliber AR should know. I think it's 3 useable inches.

[billt]

I can't think of anything more worthless. You wouldn't get 10% of the powder burned. Muzzle velocity would be all but nil. Unless you screwed around trying to handload 5.56 MM with Bullseye, or some such nonsense.

[Big Frank]

It's a 9mm Bill. But it's still worthless, unless you put a suppressor on it. You could put a can so big on it, all the gasses from supersonic ammo would slow down to subsonic velocity before they left the muzzle.

Here's my rendition of an Aero Precision EPC-9 Carbine with this 3 inch barrel. Just because it's stupid, doesn't mean it can't be EPiC. And you can quote me on that, just don't write it on my grave marker. I already made plans for that. The forend is so short there's not even room for ONE M-LOK slot on the bottom or sides. It took me all night to make this silly thing. Now I have to finish eating, and see if I can get a half hour sleep before I get up to get ready for my dental appointment. Not likely, since it usually takes me an hour to fall asleep. Maybe I can take a nap in the dentist's chair.

P.S. You can extend the stock partway and it could be more than half the the length of the entire rifle.

[billt]

My bad. I didn't pay attention to the markings. 

[Big Frank]

Here's a 5.56mm barrel with a 1:5" twist. I never heard of one that fast, but since it's only 5" long, you get exactly ONE revolution before the bullet leaves the muzzle. Even with that fast of a twist, it doesn't seem like one revolution would even begin to stabilize it. I'll bet the bullet has a lot of yaw to it, even if it does fly straight. And, unless your ammo is loaded with fast powders made for use in such an abbreviated barrel, It's probably not going to burn much of it. I think any ammo would be subsonic from a stubby barrel like that, and MAYBE the powder would continue to burn as it flew between the baffles of a suppressor. But, I'm not sure that's how that works. An integrally suppressed barrel would be way better than that slapping a can on this abortion of a barrel. You would have 10.5″ effective rifling for 16.5″ OAL barrel with a MISB AR upper from SWS Rifles, instead of 5" of rifling with a suppressor screwed on in front of it. It would be more accurate, and you would only need one tax stamp instead of two since it's not an SBR.

P.S. If the stroke of the bolt carrier is longer than the distance from the gas port to bolt face, how reliable is your gun going to be? It might work with one weight of bullet in one brand of ammo if the gas port is reamed out large enough, and the gas tube can handle that volume of gas in such a short amount of time, but this just looks like an invitation for malfunctions.

P.P.S. I want to see this set up as a short barreled M16A2. 

[Sponsor]

[alfsauve]

It would be tempting,  but I’ve never explored this.

As a pistol:
I’m guessing recoil driven, so a special BCG and bolt.  Could it be done with a less bulky recoil spring?  Special mag well adapter and mags?

[Big Frank]

The 9mm would be blowback operated and should work with the right recoil spring, but the 5.56mm is direct impingement, and I just don't see that working well. And I don't see much point in a 3" 9mm barrel on something the size of a carbine. Hardly any 9mm pistols have barrels that short. Assuming it's an AR-9 pistol with a brace, not a stock, it's till going to be big and bulky.

[Big Frank]

Here's a picture of an M16A4 rifle, courtesy of Wikipedia.

And here's a picture of what I think it would look like with this 5" barrel on it.

You know what's worse than being issued an M16 with a quarter-length barrel? Getting the command to mount bayonets.

This is your M16A4 on drugs.