AR Sponsor
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? |
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. |
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? |
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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. |
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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. 
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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. 
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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." 
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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 |
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. |
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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. |
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