AR Pistol... what length barrel? Pros and cons.

[Mtbkski]

I've been going back and forth on getting myself an AR pistol. Well after reading Emptymags "Gun in a box" thread, I'm back to wanting one. But alas, I stumble onto a problem. What size barrel do I get. I thought for sure I would go with a longer one. But Emptymag made some good points on why he chose the shorter barrel. While I was thinking I may want a longer barrel initially, now he has me thinking. Bu some of you mentioned that the round does't perform as well. What did you mean by this? I'm new to the AR platform, so this is where you guys come in.

What are the pros and cons of the various barrel lengths for an AR PISTOL? Would like to hear what you know, or think you know about the difference in barrels and which ones does what better. Advantage and disadvantages. You guys know the drill. Educate me.

[ExFlyinguy]

You could go mad digging into the ballistics

Short & sweet version- I think the .223 was designed for a 20 inch barrel, maybe it was 24" but let's say 20"

For every inch that the barrel is reduced the bullet loses velocity due to un-burnt powder escaping once the bullet leaves the barrel. Somewhere in the vicinity of 100 feet per second / inch removed maybe. Bare with me I'm winging this.

The .223/5.56 counts on it's velocity to deliver it's foot pounds of energy on target, otherwise it's basically a .22lr if the speed is reduced enough. It's basically why there is no point to making subsonic .223 ammo

I forget what I read to be the magic threshold for the .223 somehwere around 2,500 fps maybe. Hopefully somebody else can correct me.

At close ranges the issue is less important, but 2-300 yards and beyond the little bugger is about out of gas, when using barrels typical in pistol builds.

*ETA: when I typed this I jumped to the conclusion that you were talking about a .223 I doubt 9mm has any issues on barrel length.

[MD66948]

My son Mike picked up a POF 7.25 upper several years ago. It shot real well on both semi auto lowers and my Colt M16.

Here is a short video of it on my M16. I never had a AR pistol but I have had many SBRed ars. I found 11.5 to be my favorite Barrel Length. In a pistol format you may want to go shorter then 11.5. Do you have plans to suppress it? Some suppressor companies do have warranty issues with short barrels.

https://www.youtube.com/watch?v=n5Bg8fkC89U

[JDA58]

for an AR pistol.. IMO anything longer than 8.5 .... is too long.
someone on here said a 10.5" barrel is not really much of a pistol...more like a rifle without a stock

[Delkal]

Like Exflyingguy said.....the 223 was made for longer barrels and when you start out at over 3000fps the "magic" happens. Shorter barrels start to lose a lot of energy. By the time you get to 8 inches the 223 has about the same energy as a 22 Hornet in a rifle. At 4 inches it is under a 22 Mag.

Here is what you need to know about velocity and barrel length (and remember energy is mass x velocity squared). There is a big tradeoff between velocity and "coolness". For reference a 300 fps difference in 2 different cartridges with the same bullet weigh is usually considered "significant". Like a 30-06 vs a 300 win Mag. Losing 1000 fps is "very significant" and not in the same class.

http://www.ballisticsbytheinch.com/223rifle.html

[NathanB]

Depends on caliber. I've got an 8.5 300 blk sbr and a 10.5 223. The shorter you go in 223 the faster you lose velocity. That one loses about 600 fps from a 16 inch barrel

[esh21167]

Form follows function. What's your reason for wanting an AR pistol?

If it's for 'compactness', you will definitely sacrifice velocity, like has already been said. 5.56 is pretty good down to 11.5". 300 BO to 8". Want 9mm? Probably 4", lol, but there are much better 9mm options if you want a 4" barrel.

[awfroadan]

The best AR pistols would be .22LR or 9mm/40. As stated 300 needs at least 7-8" and 223 really needs at least 10". I would recommend registering the lower and doing it right with an SBR. Most agree it's a better setup. With one registered lower you can have multiple short uppers.

[MD66948]

The best AR pistols would be .22LR or 9mm/40. As stated 300 needs at least 7-8" and 223 really needs at least 10". I would recommend registering the lower and doing it right with an SBR. Most agree it's a better setup. With one registered lower you can have multiple short uppers.

I would also go with a SBR as awfroadan suggested. I am currently building my 4th AR15 SBR for one of my sons. It is a fun project and your caliber & configuration options are many. The AR15 Rifle is a System and a Platform that allows the shooter to build it, configure it and accessorize it any way he or she wants for their needs and pleasure.

If you haven't done a ATF Form 1 for building an SBR please feel free to contact me with any questions you may have. I would be glad to walk you through it.

Dane

PS: Here are two AR 15s that I built for two of my sons.

[aubie515]

It really depends on what caliber you are looking at as well. On my 300BO...the ideal barrel length is between 8.5" to 10.5"...I went with 10.5" for my 300BO as anything longer than 10.5" is a waste since the powder burns off between those lengths.

For my 223 AR15...I like 10.5" to 12.5" as I would not go under 10.5" because I want as much velocity I can get from a short barrel.

You really should chrono the speeds of ammo you are using, as some bullets will need X velocity to expand/fragment. Guessing what your velocity is going to be at Y distance is not a wise choice.

It all boils down to what the intended purpose of the AR15 pistol.