9mm Velocity in 7" barrel vs 10.5" barrel

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wicked_police

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There's a few threads about pistol caliber carbines, so I figured I'd add another one.

Has anyone done any comparisons between the 7" AR upper and 10.5" AR uppers for 9mm AR's?

I'm going to build myself another one (as usual, regret selling something after it's gone), and want to know if the difference in velocity is significant enough for the extra barrel length. And before anyone asks, I plan on doing precision shooting at 300-500m with it.

Thanks.
 
When I was buying a 16 inch 9mm AR upper I looked into velocities of 9mm vs. in a pistol, and while I can't remember the numbers, there was very minimal velocity gained in even a 16 inch barrel. Something like only 100-200 fps gained between 4 and 16 inch barrels.
 
Looks like I actually saved this chart on Photobucket, from my thread a couple years ago.

For your 2 options there is little to no difference, at least with this load.

Here you go:

9federal147hs.gif
 
Wow... Not much difference at all. That load is close enough to what I have on hand so it's good data.

That's exactly what I was looking for.

Thanks a bunch.
 
Makes sense.

It uses pistol powder, which burns in a way to achieve maximum velocity from a short barrel. Even with a longer barrel, you will not be able to achieve much more velocity unless you start altering your powder.
 
heckler said:
...not to use heavier than 124gr. in a carbine.
Click to expand...

The only gun we use lighter than 147gr in is the MP-5SD. The extra barrel length gives it just enough of a boost to get the round supersonic, which kind of defeats the purpose of suppressing the gun....

Now that I'm thinking of it, I'll grab one of the MP-5's from work and get some velocities, and compare that to my pistols.

Finding the difference between 4" and 9" should give me a rough idea of what to expect in a 10.5".
Regardless, I'll most likely stay with a 7" for the upper.
 
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