Rifle versus Carbine velocities.

Ammunition, reloading, shooting, etc
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operavoice
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Rifle versus Carbine velocities.

Post by operavoice »

I've been running 36.6 grains of IMR 4064 behind various 180 grain SPRN, Interlock, and spitzer projectiles.
For the most part, my velocity runs in the 2050 - 2075 range with a 24" barrel (the exception being Barnes solids, which ran 100 fps faster, and I stopped using them after 4 rounds).
The brass comes out of the chamber surprisingly cool, even after 20 rounds, you can eject the brass directly into your hand without discomfort.

So, to my question, common "theory" is that you lose 50fps per inch as you cut down a rifle barrel.
If a 30" antique barrel is "running a hot load" at 2400 fps, in theory, 2100 fps would be a hot load for a 24" carbine, but my brass sure as hell isn't acting like it's a blazing load.

What is the reality?
For carbine owners, what kind of velocities are you getting with 180 gr jacketed bullets?

The historical data doesn't make any sense.
According to Wikipedia ( and I do take that with a grain of salt), the 30" rifle firing 220 gr clocked 2000 fps, while the carbine was only 40 fps slower out of the 22" barrel.

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butlersrangers
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Re: Rifle versus Carbine velocities.

Post by butlersrangers »

'operavoice' - I cannot throw much light on the subject of your question.

I usually stick to published data in manuals and just work toward accuracy, with low pressures & economy.

I don't own a chronograph, so I basically accept the velocities reported in manuals or by careful experimenters.

With the .30-40 Krag, my biggest concerns are chamber/barrel pressure, brass life, and, especially , group size.

Some thoughts:
With a history of 130+ years, the Krag cartridge has known many propellants.
Finding a successful smokeless powder, in the beginning years, was a difficult challenge.

The 30 inch Krag barrel, possibly, was not the best ballistic choice.
It may have been chosen in part for length of bayonet 'reach'.

Overly long barrels at a certain point, (with bullet friction and more efficient powders), may bring diminishing velocity returns.
For instance, if a 26 inch barrel is the ballistic 'sweet-spot' with the .30-40 cartridge and improved propellants & projectiles, four more inches of barrel may just slow things down.

Maybe something like this is happening and might explain the close velocity results of 22" and 30" Krag barrels.

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butlersrangers
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Re: Rifle versus Carbine velocities.

Post by butlersrangers »

Doing a bit of reading, it appears longer high power rifle barrels, help increase bullet velocity, out to 40 some inches.
(But, not all that much).

Also, shortening rifle barrels does not cost all that much in bullet velocity, but, more than I reckoned. (I was quite likely mistaken on several points, in my first post).

I found an interesting paper by Brandon Lewis Clark (Honors College - University of South Florida - May, 2011), titled:

"Effects of Barrel Length on the Muzzle Velocity and Report from a Mosin-Nagant 7.62X54R Rifle"

Page 23 of Mr. Clark's paper contained this interesting chart, showing velocity loss, related to shortening the barrel in 2 inch stages. Nice experiment Brandon!

'Operavoice' does have a good point in his suspicions about the 22" Krag barrel only losing 40 fps, (per Wikipedia), when compared to the 30" rifle barrel.

The 7.62X54R is a more powerful and higher velocity cartridge than the .30-40. Cutting the Mosin barrel, from approximately 29 inches to 22 inches, dropped bullet velocity just a bit less than 200 fps.

FWIW - My reprint of the 1917 Ordnance Manual, for Model 1898 Krag Rifle and Model 1899 Carbine, gives a muzzle velocity of 2,000 FPS for the Rifle and 1,920 FPS for the 22" carbine, using the Ball Cartridge with a 220 grain projectile.

(The Manual gives a difference in velocity performance of 80 FPS, between the two barrel lengths, this is greater than 40 FPS, but, not the almost 200 FPS found in the Mosin barrel experiment).
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FredC
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Re: Rifle versus Carbine velocities.

Post by FredC »

Would expect the "burn speed" of of individual powders would have something to do with the velocity difference between your different barrel lengths. On could use Quickload and run all kinds of barrel length, bullet weight and powder combinations. Off the top of my head a safe load with a moderated burn speed like 4064 or Varget with a 150 grain bullet would show less difference between carbines and rifles than using the traditional slower powders and 200 grain bullets. When you run Quickload, it does tell you what percentage of powder is unburned with the chosen barrel length. I have not actually tried doing this but I expect it would render helpful insight.

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