Optimal barrel length for best ballistics in a 9mm carbine/sub gun clone?

Optimal barrel length for best ballistics in a 9mm carbine/sub gun clone?

Good starting point... http://www.ballisticsbytheinch.com/9mmluger.html

The sweet spot for 9mm seems to be around 15-16" barrel length. +P variety will be zipping along around 1300-1350fps. 147gr bullets will be very good for penetration, however slightly slower.

+1

9mm, 40SW, 10mm - up to 16" barrels
45 acp - up to 8" barrels in PCC.

Sorry marlin camp carbine and HK USC guys, your 230 grainers actually are slowing down in those 16" barrels. More stablized but slower.

Rifle = high pressure

There is a plus to a 16 barrel 45 acp, it is very quiet.

Appreciate the helpful posts gents

That has not been my experience. Using both fast (Win 231 and Clays) and slow (Blue Dot) powders, I still experienced an increase in velocity from two different 5" 1911s (one with a factory barrel, one with a "match" barrel) vs. a 16" Marlin Camp 45. It's not a huge increase, but it is definitely there, and has been verified on more than one occasion.

I have a 135 fps. difference using a 200 gr. LSWC and Win 231.
A 91 fps. difference with a 200 gr. plated SWC and Clays.
A 130 fps. difference with a plated 230 gr. RN and Win 231.
A 231 fps. difference with a plated 230 gr. RN and Blue Dot.

Go play with a chronograph and see what you come up with.

hmm. So a longer barrel is better. Wonder why all the sub guns are shorties? much have to do with maneuverability, not ballistics.

I think Duncan was comparing the 16" with the 8". You may see an increase in velocity from a 5" to 16" but you'd see more of an increase from 5" to 8" and you'd see a decrease from the 8" to 16"

You're right. I shot an HK USC and it was very quiet.

I think that you will not gain much vel. after 10" to 12" with most ammo

Maybe. Don't know.

I'll have to drag some factory ammo and an assortment of guns out to the range to chrono some time.

if using slow powders like power pistol in a 16" 9mm you can pick up some serious velocity with the lighter bullets. if your planning on running a subsonic load then there's no reason for a longer barrel. for factory ammo I think the 10" range may be ideal

I have clocked several 9mm and .45 carbines. The 16" barrels produced the highest velocities, though as noted, the increase over a moderately shorter barrel is not all that great.

In 9mm, the 147 grain bullets are probably the best choice for a hollow point load, as they will be less likely to over expand and under penetrate. Loaded with max amount of Power Pistol, and 147 grain JHPs, my AR carbine is pretty close ballistically to a 4" service revolver.

Different barrels can of course produce different results. It is amazing how much seemingly identical barrels can differ in velocity.

So what you're saying is that after about 8 inches, the powder gasses have expanded such that their pressure drops to below atmospheric, the net force on the bullet is now backwards toward the gun, any further inertial movement of the bullet forward in the barrel causes a suction effect, and the bullet is slowing down?

Funny how the gas still seems to blow out away from the barrel instead of getting sucked back in once the bullet isn't blocking it anymore...



Yes, at some point as a barrel's length keeps getting bigger, the amount of gas produced by the burning powder wont be enough to keep a net force on the bullet, and the cumulative friction from the barrel becomes significant, but I know the first isn't happening inside 16 inches, and I doubt the second is either.

Why would the bullets start slowing so soon?

It isn't dropping to below atmospheric, causing a vacuum. What they are saying is that the powder is consumed inside the 8". After that, while there is still pressure behind the bullet of the high pressure gases, the drag of the rifling and the barrel is greater, causing the bullet to decelerate. That is also why a 16" .45 is quieter- the powder is consumed. Also no real muzzle flash. The .45ACP was designed first and foremost to be shot in a 5" barrel.

And yes, if the barrel was 12 feet or so, so bullet could conceivably stop in the barrel.

HERE is the .45ACP chart from the same place as the 9mm one I posted much earlier in the thread.

The fastest barrel length for the different rounds: 18, 16, 14, 16, 16, 16, 17, 11, 11, 16.

The amount of additional velocity gained by going from an 8" barrel to a 16" barrel: 6%, 10%, 10%, 4%, 7%, 11%, 8%, 3%, 5%, 4%. Four percent more velocity may not be worth carrying twice the barrel, but 11% may be.

If the data is accepted at face value, then 16" is the optimal length for firing a 45ACP. I think the data is bad since almost every round tested was slowing down as the barrels were getting longer UNTIL they hit the 16" barrel. Almost every round mysteriously sped back up out of that barrel, making me think it wasn't controlled for as a variable in the testing.


The 9mm data is even more supportive of just using the longest barrel you can find if all you care about is velocity; to the limit of their testing with 18" barrels, almost every round was still speeding up. What it tells me, as someone who almost exclusively shoots 9mm, is that once you've made the transition from a 4" or 5" pistol up to a 16" PCC, your weapon choice should be based on things other than barrel length.

I noticed the same trends. While I would like to see other similar tests/results for comparison, it has made me seriously rethink SBRing one of my 9mm ARs (which I had been planning to do). But I still may anyway, as I shouldn't be "losing much gain" and short, handy ARs are very appealing to me... esp. if I am going to add a suppressor at some point.

Thanks for the great info!

Take these numbers and plug them into this Program.

Then you can see why most SMG's that have hand guards, generally have barrel lengths less than 10".

They key to the issue of barrel length versus bullet velocity in 45 acp (and any caliber you choose to discuss) is this:

Lighter bullets are generally loaded with slower burning powders that can utilize longer barrel lengths. You will see a greater rate of velocity increase with 185 grain projectiles loaded with Alliant Power Pistol powder in a 16" barrel than you will with a 230 grain projectile propelled with a super fast powder like Bullseye or Red Dot. Most 230s would be moving about the same velocity or less in a 16" than an 8" or 10" and most 185s or lighter woud be going faster, with factory loads, as they optimise there loads for velocity with the use of proper powders. I would imagine a special load with a mid-slow powder like Blue Dot and a special 140-165 grain bullet would be traveling faster in a 24" barrel than a 16" barrel.

If it were me, I don't see carrying around any more than about 7-9 inches of barrel on an SBR carbine chambered for a pistol caliber. Maybe a 7.62 x 25 would get a 12 incher. Your standard non-bottlenecked pistol cartridges will shine at 7-9.

Also, if you plan to use a suppresor, it just so happens that many standard 124 grain factory loads go subsonic at about 3-4 inches of barrel. Food for thought.

––-Catter

One thing I've noticed with my 45carbine is that the 100yd POI is very close to the POI of a 25yd Zero. I never have to change the sights when going between 25 and 100yds.

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