9mm Barrel Lengths..........what is TOO short?

AR Sponsor:

[ARCHIVED THREAD] - 9mm Barrel Lengths..........what is TOO short?

Posted: 1/31/2006 7:37:54 AM EDT

So I need to have a short pistol barrel made. Was thinking 6" but could do 5"-8". Will the 2" extra affect accuracy? What length is really required for the 9mm bullet and still be a good shooter?

Posted: 1/31/2006 8:40:25 AM EDT

[#1]

I've heard that barrel lenghts above 10 inches actually slow down the 9mm round. Just FYI.

Posted: 1/31/2006 10:16:21 AM EDT

[#2]

Quoted:
I've heard that barrel lenghts above 10 inches actually slow down the 9mm round. Just FYI.

That is incorrect. There used to be a website (link) but it appears to have either disappeared or they're just temporarily down. Anyway the site listed the data they obtained from testing various brands and types of ammo through 9mm carbines with different length bbls. The results showed that in every case, a longer bbl imparted more velocity to the round. IIRC, the min/max range of velocity increase was from 5% to around 15%.

Considering that, longer (>10") bbl length on a 9mm carbine doesn't really give you any significant advantages, at least not to the point that 5.56mm rifles get. Besides, within the useful range of a 9mm carbine, bbl length is not going to have a measurable effect on accuracy unless you are using iron sights and placing your front sight as close to the end of the bbl as possible.

I had a 16" bbl HK-94 (civilian MP5) and now I have a 11.5/5.5" FH AR 9mm and the AR is just as accurate as the HK.

Posted: 1/31/2006 10:31:06 AM EDT

[#3]

My chrono says that my Sub 2000's 16.1" barrel offers a 29% increase in velocity vs. a 5" Taurus PT92 for the same ammo.

Posted: 1/31/2006 10:57:31 AM EDT

[#4]

I was thinking about a 6" barrel on the AR.

Posted: 1/31/2006 11:41:11 AM EDT

[#5]

Here are my findings. Take this for what it's worth (about 2¢ more than you paid for it):

Posted: 1/31/2006 12:04:37 PM EDT

[#6]

Wouldn't an AR shoot different then a pistol?

Posted: 1/31/2006 12:34:02 PM EDT

[#7]

Quoted:
Wouldn't an AR shoot different then a pistol?

Blammo's chart indicates that. The Kel Tec Sub 2000 is carbine. You may have noticed that already so please excuse me if you did.

And thank you for posting that Blammo. I couldn't remember the exact velocity gain from a 16" bbl.

BTW, wouldn't a longer bbl lead to slightly more reliable fragmentation with JHP rounds?

Posted: 1/31/2006 1:05:12 PM EDT

[#8]

No, I mean a 6" AR 9mm will have different rates then a 6" handgun.

Posted: 1/31/2006 1:21:14 PM EDT

[#9]

Quoted:
No, I mean a 6" AR 9mm will have different rates then a 6" handgun.

If you mean that an pistol caliber AR w/a bbl the same length as a pistol will have a different velocity, then no, they should be pretty much the same. They're both essentially blowback operated weapons. In other words, assuming the bbls are the same, the round will achieve the same velocity in either a pistol caliber AR or a handgun.

Posted: 1/31/2006 1:24:24 PM EDT

[#10]

I can't imagine the barrels are the same.

Posted: 1/31/2006 1:49:50 PM EDT

[#11]

Quoted:
I can't imagine the barrels are the same.

While I cannot disagree with you on this because I am not 101% sure they would be the same, I also cannot agree with you because I cannot think of what would be different about them, at least from a ballistics perspective. Sure, some pistols (and even some rifles) have polygonal rifling (e.g the HK USP pistols) but to compare a pistol caliber AR bbl to a handgun bbl fairly, they would both have to have the same rifling.

There's a board member that runs this site but I don't recall his user name at this time. He's on these boards often so I would be surprised if he did not see this post. I would bet he would be able to give a definitive answer to your question.

Posted: 1/31/2006 2:18:32 PM EDT

[#12]

I can't imagine a significant difference between a 5" 9mm AR barrel and a 5" pistol barrel. Like Matt_B said, a different type of action, a chrome lining, polygonal rifling or a stainless barrel might make a difference, but I doubt any of them would have a major influence.

Notice that my baseline is a Taurus PT92. I don't know for sure, but I strongly suspect that its barrel is substantially similar to a typical AR 9mm barrel.

With that said, I will gladly accept a 9mm AR barrel for cut-down testing. If someone wants to donate one, I'll run several types of ammo through my Oehler 35P, cut the barrel down and repeat until we have a nice set of data where we can accurately correlate velocity to barrel length.

Posted: 1/31/2006 2:44:34 PM EDT

[#13]

Quoted:
I can't imagine a significant difference between a 5" 9mm AR barrel and a 5" pistol barrel. Like Matt_B said, a different type of action, a chrome lining, polygonal rifling or a stainless barrel might make a difference, but I doubt any of them would have a major influence.

Notice that my baseline is a Taurus PT92. I don't know for sure, but I strongly suspect that its barrel is substantially similar to a typical AR 9mm barrel.

With that said, I will gladly accept a 9mm AR barrel for cut-down testing. If someone wants to donate one, I'll run several types of ammo through my Oehler 35P, cut the barrel down and repeat until we have a nice set of data where we can accurately correlate velocity to barrel length.

That is funny because he has a barrel he if getting rid of on the EE. By the way WS4lif I want the barrel and the M4 upper.

Posted: 1/31/2006 3:29:42 PM EDT

[#14]

Doh! I'd love to buy it, but all my fun money is tied up in 2 projects that are in the works right now.

But I do take donations and I deliver great analyses! Maybe I should park my butt on the street corner in Hartford with a cardboard sign that says "Will chrono for barrels."

Posted: 1/31/2006 4:01:53 PM EDT

[#15]

You might see a difference in accuracy from having two different twist rates as well. Also, it is my understanding that right in the 5"-8" barrel length, you see 147Grain bullets wanting to go sub/super sonic. I know that you have plans on a can on you 9mm, which is why I mention this. If you go with a 5" barrel it will be easier to find off the shelf ammo that will be subsonic (147 grain).

Nox

Posted: 1/31/2006 5:54:25 PM EDT

[#16]

Thanks for the info on barrel length. I was gonna cut my 9mm down to 9.5. Now, I'll have to think on it.

Posted: 1/31/2006 7:09:36 PM EDT

[#17]

I'm running a 4" barrel....seems about as accurate or better than my pistols at 25 yards

Posted: 2/1/2006 12:44:05 PM EDT

[#18]

I HOPE SO!

Posted: 2/1/2006 5:09:08 PM EDT

[#19]

Quoted:
I'm running a 4" barrel....seems about as accurate or better than my pistols at 25 yards

That's the shortest I've heard of. Have a pic?

Roy

Posted: 2/1/2006 7:27:45 PM EDT

[#20]

Quoted:

That's the shortest I've heard of. Have a pic?

Roy

Old pics - I've switched to a Hahn block. The barrel looks longer in the pic than it actually is, I have a TROS adaptor on the end.

Posted: 2/6/2006 9:39:37 PM EDT

[#21]

Quoted:
Quoted:
I can't imagine the barrels are the same.
While I cannot disagree with you on this because I am not 101% sure they would be the same, I also cannot agree with you because I cannot think of what would be different about them, at least from a ballistics perspective. Sure, some pistols (and even some rifles) have polygonal rifling (e.g the HK USP pistols) but to compare a pistol caliber AR bbl to a handgun bbl fairly, they would both have to have the same rifling.

There's a board member that runs this site but I don't recall his user name at this time. He's on these boards often so I would be surprised if he did not see this post. I would bet he would be able to give a definitive answer to your question.

\

Somehow I missed this the first time around, but I ran into it tonight...
I don't think there is really a minimum length, you could probably go back to 3" if you want, but you would lose a bunch of velocity.
5" to 6" is probably where you want to be.
Differences between AR's and Pistols in the same length barrel is going to be a matter of breeching style and any differences in rifling.
I can't tell you if a blowback action such as the AR loses any velocity vs a browning locked breech system such as the mantioned taurus or glock pistols.
Differences in rifling styles would likely have more effect that the breeching system.

If anyone needs a short 9mm barrel, I just got some RRA barrels in that I can shorten.
I think a couple are pre-sold, but there are still some left as well.
$185 for the barrel, $40 to shorten and thread to any common spec and $10 shipping.
I recommend 9/16-24 or 5/8-24 as they give you a stronger thread junction than 1/2-36 or 1/2-28.

Posted: 2/7/2006 4:18:38 AM EDT

[#22]

Just for S&G, I will throw in my experience with shorter vs longer barrels and 9mm ammo. I did some chrono testing with various 147 gr. loads, trying to find a subsonic one and all of them were subsonic from a pistol barrel, but supersonic from an 11" SMG barrel. I then tried some of the Samson 158 gr. subsonic and I found that the velocity was actually higher from the pistol barrel!

This is pretty specialized ammo, but apparently there's an exception to every rule.

[ARCHIVED THREAD] - 9mm Barrel Lengths..........what is TOO short?

AR-15 » Rimfire and Pistol Calibers

AR Sponsor:

Warning

Confirm Action

About AR15.COM

Stay Connected

Newsletter

Contact Us