How much velocity loss takes place when shortening a rifle barrel?

[GatorFarmer]

A simple matter really. My inexpensive sporterized 1917 has a singular glaring flaw remaining now that the ejector has been replaced. The 26 inch barrel has a large slot in it where the front sight used to reside. My thought was that perhaps the rifle would look better and be a bit lighter if I had 4 inches or so of the barrel removed and recrowned. The gun is a .30/06. For every inch of barrel that I remove, how much velocity am I likely to lose? Is there a major risk that the shorter barrel will be less accurate? Sight radius is not an issue as the rifle is scoped and the iron sights long ago removed.

 

[Rustyt1953]

Here's a really good article on that very caliber.
By one of our own no less.
The Myth of Barrel Length and Velocity Loss - Guns.com

 

[BAM-BAM]

check out........ Ballistics by the Inch

 

[eyegots2no]

Bob Milek wrote an article years ago where we started with two rifles, a 6mm and a 280. He started at 24 inches and at each whack he recorded velocity and accuracy.

Accuracy differences were meaningless and not consistent or linear.

On velocity with some factory ammo on both the 6mm and the 280, he lost velocity at each whack---the loss was not same each cut---maybe 13 fps at one cut or 35 then 19 fps the next---just not that great of a deal although once down to 18 inches he hade lost around 200 fps or so on each if I remember right.

On the reloads he used, he gained 100 fps after cutting 3 inches off the 6mm, then he started losing some velocity at the remaining cuts.

On the 280, he gained 74 FPS after cutting off the first inch, then started losing velocity after that.

SO...............

 

[DWalt]

There is no fixed rule, as chopping off an inch from a 26" barrel will make less of a velocity change than cutting an inch from a 20" barrel. There is a website I remember relating some very extensive experimental testing done using many different loadings of.223 ammunition in a rifle barrel which was cut off inch by inch, until it got to around 8" or so. On average, as I remember, the MV change was about 40 ft/sec/inch, but it differed with different loadings and different barrel lengths. For handguns, I'd think the results would be different. If you happen to have an internal ballistics program such as Quickload, you can use it to estimate the effect of barrel length on MV. I have done that in the past, but not for handguns.

 

[GatorFarmer]

Here's a really good article on that very caliber.
By one of our own no less.
The Myth of Barrel Length and Velocity Loss - Guns.com

The comments section of the article leads to a 40 page paper on cutting down a Mosin. It claims an average velocity loss of 25 fps per inch. Ballistics by the inch only lists a .223 as rifle calibers tested. That shows an extreme spread whereby if a gun goes all the way down to a 3" bbl that velocity lost is around 2000fps.

Thus it seems that the answer I thus far find is "it is complicated" and "it depends". Which while the answer to many things in life still leaves some room to ponder.

 

[Rule3]

Correct, there are many variables, such as caliber and bullet being the main ones. You can only guesstimate with Velocity by the inch. The only way to know what the loss will be (and can not be reversed!) is to chronograph it now and then chop it.

How about a picture, how much would it be to fix the looks of the flaw??

The front site is now gone? Leave it alone.

 

[Hellraiser]

I've always wondered... how long would a rifle barrel have to be... in order for the bullet to suck a vacuum and come to a stop before exiting?

Whups... I better watch out... a legislator from the State of California might read my post.

Nevermind.

 

[Roadtrash]

Now there's a question I never thought I would see but it does make me wonder as well.

 

[Texas Star]

The rule of thumb that I've seen most often for .30-06 class ctgs. is about 25 FPS per inch. I think that's what Jack O'Connor published.

You can get by nicely with a 22" .30-06 or .270, but if you stop at 24 inches and use the factory made accelerated velocity loads, you'll fare better on velocity.

I don't see the point of cutting Magnum barrels below 24 inches. I think the std. Winchester M-70 in .30-06 is an excellent all-round rifle. If you're more after deer or wild sheep in the mountains, O'Connor's choice of a 22-inch bbl. is a very solid idea, and it works well in most hunting situations. But if you're shooting moose, elk, or big bear, the 24-inch bbl. with hot loads gives an edge.

In Magnum revolvers, the usual rate is some 40 FPS per inch. However, the 140-145 grain bullets average at least 1200 FPS from just a three-inch bbl., so remain very potent. Winchester's 145 grain Silvertip .357 has an excellent street record. One detective who's examined the results in a number of police shootings told me that it works almost too well, if that is possible. I suspect that from at least a four-inch barrel, it's lethal in side-on shots on deer and antelope. Probably a good javelina load, too. I'd trust it on cougar. Rather have more bullet on bears and big pigs.

 

[Gamecock]

If you are hunting deer, it won't notice the difference between 26" and 16".

 

[oldRoger]

It is complicated (and certainly not linear); the gas pressure falls as the bullet travels down the barrel, the pressure curve peaks near the chamber and has a long tail. As long as the pressure is sufficient it will push the bullet a bit faster in a long barrel. How much you say?

One of the usual aspects of the cut an inch off and check school of science is a consistent use of factory ammunition. Factory ammunition is optimized for a specific barrel length. So it is not really surprising that little velocity change may be seen in barrels close to the optimized length.

In the .308, barrels generally are 20-22” and when you find one at 16” it is not unusual to see a 150-200 fps drop in velocities. The Parma Shooters use a 30-32” barrel and hand load to achieve high velocities with their 155 grain bullets.

Most .22LR ammunition is optimized at 16-18” and a 28” target rifle will usually see some drop in velocities compared to 18”, it is quieter though.

How about the 30-06? Well in days of yore, 24-26” barrels were common in 30-06, my M1917 was rebarreled with a 26”.
Will you likely lose some velocity cutting it down 4”? Yes, perhaps 80 fps will be lost.

Does that matter? It would to me shooting at a 500 yard target, probably not to many others.

 

[BruceM]

If you are hunting deer, it won't notice the difference between 26" and 16".

If that were true, everybody would ditch their .30-06 for a .30-30 and not look back. The fact is that velocity is needed for other things besides killing power.

As to the OP original question, it all depends. It's not as simple as Dave LaPell's article implies either. I think Bob Milek's article is probably closer to what happens than most others. Personally, I kind of favor 22" barrels for standard calibers such as the '06 and a 24" barrel for magnums such as the .300 Win. Mag. in hunting rifles. That said, there are always exceptions.

Bruce

 

[jlrhiner]

Grab your hacksaw and go for it. Quit being a sissy.

(This post is not meant to insult any sissy's who may read it)

 

[Arik]

I know if you go from 16 inch to 8 inch barrel for 7.62x39 you only loose 200fps

 

[Big Cholla]

Make the decision simple for yourself; write a nice email letter to several major factory producers of 30-06 ammo and ask them which 30-06 ammo do they load using a rifle powder that is optimized for the length that you want to cut and crown your barrel. Over a period of time as the return emails come back you might just find an ammo that is factory 'tuned' for your length of barrel. Like many others mentioned, I think you might be obsessing just a little. I handload and have a chronograph. I would just find my own 'tuned' load and go for that with any length barrel that I choose. Again, maximum velocity attainable never has made much difference in the field. It is always a matter of bullet placement. ..................