Lenght vs Velocity

[Crow BarKeymaster]

In another thread, the usefulness of a pistol length carbine was brought up.
Not sure where it started, but the general mantra in the firearms world, was for every inch removed from a barrel (even regular rifle rounds) you would lose anywhere from 25 to 150fps.
I know I thought the same!

While at Tractor Supply yesterday waiting in the checkout line, a magazine caught my eye with the sub-title of Length vs Velocity.
The author of the article, took a pistol carbine of 16inches, ran 10 rounds of 12 different types of 9mm ammo through it, across a chrony, recorded the results.
He then sawed off an inch of barrel and repeated the experiment. And he continued to do so until he only had 2inches left.

Super Vel 90grn JHP+P at 16inches = 1767. At 5inches = 1594. A difference of 170fps.
Browning 147grn J-FP at 16inches = 1176. At 5inches = 1058. A difference of 118fps.
Those are just two I picked out.

Interesting, educational, and you wont really know until you get out there and actually crunch the numbers.
Firearm mantra may not be all it is cracked up to be.

Additional observation, this was a Guns&Ammo publication called Carbine. I was shocked at the level of writing, it was better!! For me G&A really fell down around the time they released their Zombienation! tome, and backed it up with a sub-site called the same.

[Anonymous]

I am not a gun expert by any means, so I look at it just from the physics textbook point of view. The pressure behind the bullet decreases as the bullet move along the barrel. I would guess that if the barrel is long enough, the pressure would be insufficient to accelerate the bullet any more and the friction in the barrel would actually slow it down. So probably there is one combination of powder load, bullet weight, and barrel length that gives you the maximum muzzle speed. Putting a load designed for a pistol in a carabine might give you better accuracy due to the bullet spinning faster and aiming with a longer gun but probably it is not going to do much for the bullet speed. If it would significantly increase the speed, probably that load is too much to use in a pistol. just my early morning 2 cents, likely worth less than that. 🙂

[Crow BarKeymaster]

From what I have learned from my reloading experience, you want to match the case capacity, the weight of the bullet, length of barrel with the correct corresponding powder burning rate.
In short, you want to maximize the pressure of the powder burning before or just as the bullet exits the muzzle.
A 125grn .30 round is traveling faster, and would require a faster burning powder than say a 168grn.
Bullet jump, and chamber pressures also are a factor in this, but that is a different subject.

Reading the article, looking at the differing bullets, knowing most were meant for a pistol form factor, I was left wondering if the results would be different with handloads taylored for carbine length barrels and using the corresponding powders.

[Anonymous]

I would guess that your handload would behave differently. You would get probably higher muzzle speed in the carabine. If you would try to shoot the same load from a 2 inches barrel, as they did in the test, the speed would be lower (can’t guess how much lower) and you would get a big flash because the powder would continue to burn after the bullet left the barrel.

I don’t know what length of barrel ammo manufacturers use when they test the muzzle speed for their cartridges. Probably that’s the length they optimize for.

[Crow BarKeymaster]

A quick look at the Nosler reloading manual, they have listed a 4inch Douglas barrel.

[Anonymous]

You pick my curiosity, I’ve found these two test done on standard manufactured cartridges for 9mm and 45ACP.

https://www.ammoland.com/2017/03/45-acp-velocity-testing/
https://www.ammoland.com/2017/03/9mm-velocity-testing/

Interesting that a longer barrel in 9mm yield a higher muzzle speed but that’s not generally true for the 45. Unless there is something else at play I am not aware of. And there is a lot I do not know. 🙂

[Crow BarKeymaster]

I think that is where pressure comes into it.

When I am loading to reduce bullet jump, exceeding SAAMI specs/COL, I get higher pressure, and increased velocity, using the same grns of powder.

Disclaimer! Unless you are an experienced handloader, DO NOT exceed SAAMI specs or COL!!

Edit: Oh! If I only could afford a pistol-caliber carbine in .45ACP, I would like to do a ladder work up, to include differing COL and bullet types!
That dang money thing!
Shudda played the Powerball . . .

• This reply was modified 1 year, 7 months ago by  Crow Bar.

[JATAParticipant]

“In another thread, the usefulness of a pistol length carbine was brought up.”

Crowbar, could you link to this?

I have been wondering about a pistol length carbine (you’re referring to the AK and AR pistols that have become so prolific, right?) and it’s applications in urban SHTF situations.

I recall reading in one of Selco’s articles (in his eBook) that Selco appreciated having a folding stock AK in room-to-room work. And so I thought “well, why not a pistol AK/AR?” In addition to conceal-ability (not sure if that was important during Selco’s war) and less weight, it would be less likely to snag up on rubble. In an urban situation I don’t believe the velocity issue will be important.

Anyway, I am interested in reading what other people have to say about those “toys”; so if a link can be provided, I’d be grateful to ya.

[Crow BarKeymaster]

@jata,
Page 2 of this thread (??): https://forum.theorganicprepper.com/topic/weapon-basics/page/2/

[JATAParticipant]

Skimmed through, it seems like the thread is mostly about pistol caliber carbines, not rifles in pistol variations.

[WhirlibirdParticipant]

This may help.

http://www.ballisticsbytheinch.com/

[Author]

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