Barrel length and fps

How many fps do you lose or gain per inch of barrel length?

 

While I can not verify this, I have read you gain or lose approx 10 fps per inch for shotgun barrels compared to a 30" test barrel chronographed 3' from the muzzle.

 

So, do we gain or do we lose 10 fps per inch?
Or, does it depend on which side of the 30" mark?
Do we gain velocity as we go from 0" to 30", and then lose as we go from 30" to a longer length? I.e. is 30" the magic number for velocity?
Or does it even matter?

 

I guess my question would be how do you get how much you gain or lose with different length barrels with a 30” test barrel. You would need other length test barrels to know…

 

I could be wrong but I don’t think the targets going to care about a couple of fps. Prove me wrong

 

Beyond barrel lengthy interior finish and bore diameter can be another way than determining when away leaves the barrel

Dennis DeVault compared one of his barrels to a Silver Seitz-His barrel was 33" & the Seitz's barrel was 34"--with an electronic timer a wad AA @ 1145FPS left his barrel ahead of a AA silver bullet" @1250 wad--all I know is why? do so many K,P & Seitz owners send their guns to Tommy for tune ups ?

 

Lots of interesting info at SAMMI.org about ammo testing which most manufacturers adhere to.

SAMMI specifies the barrel lengths, chamber dimensions, and choke constrictions of barrels used for testing velocity and chamber pressure.

For LEAD Shot (not slugs) test barrels must meet the listed requirements.
Barrel lengths +/- .062" ....Choke constrictions for Lead shot +/- .005"

10 ga ...32" length -- .035" constriction
12 ga ...30" length -- .031" constriction
16 ga ...28" length -- .030" constriction
20 ga ...26" length -- .025" constriction
28 ga ...26" length -- .022" constriction
.410 ...26" length -- .020" constriction

For 12 gauge, a 28" barrel may have approx 20 fps less than a 30" barrel, and a 32" barrel may have approx 20 fps more than a 30" barrel.
....As said previously, I can not verify this statement as I read it on the 'net.

Keep in mind that SAMMI specifies chronographing at 3 feet from the muzzle. ....I can't imagine a similar change in fps at target breaking distances.

Since porting supposedly reduces recoil, does it also reduce velocity since pressure is reduced before the wad leaves the muzzle ??

Interesting trivia, but it should not matter to the shooter, or his ability to break the target.

 

Doesn't sound like it.

 

The exact amount of velocity gained or lost per inch of barrel length can vary depending on a number of factors, such as the type of ammunition, the firearm, and environmental conditions. However, as a general rule of thumb, you can expect to gain or lose approximately 20-30 fps of velocity for each inch of barrel length.

For example, if you were shooting a .308 Winchester cartridge from a rifle with a 20-inch barrel, and you switched to a rifle with a 22-inch barrel, you might expect to gain around 40-60 fps of velocity. Conversely, if you switched to a rifle with an 18-inch barrel, you might expect to lose around 40-60 fps of velocity.

 

See post #3.

Which is it, gain or lose? On what does it depend?
Gain or lose for each inch of barrel length beyond/less than what length?
I.e. what is the optimal....for MV....barrel length in general? I think that is the question.

The question still has not been answered.

 

That’s fine, honestly- it’s something to talk about on the ‘net but in real life target shooting it doesn’t matter one bit. For rifles, ok, that’s what most handloaders have chronographs for- shotguns? It doesn’t matter one bit…

 

I think it increases pressure as the bullet in a rifle is in the barrel longer . There should be a pressure increase in a shotgun also. If you load the hottest loads it could be a problem but 1145 not an issue.

 

May not matter to you, but the OP has asked the question.
Actually, doesn't matter to me either, but apparently it does to some folks.
(If you don't think it's important enough, don't respond to the thread.)

 

This can be found in cyber-land .....

"Questions concerning barrel length as it affects shotshell ballistics generally revolve around how much barrel length affects velocity, with occasional questions about how barrel length affects pressure. I can put pressure concerns to rest with one ballistic fact: While it was an issue with different-burn-rate black powders, it simply is not an issue these days with smokeless powders. The reason is that smokeless powders used in today’s shotshells, regardless of their burn rate, are essentially all burned up within five inches of the chamber."

"As to how much velocities of smokeless-powder loads are affected by barrel length, that is a bit more complicated. But to simplify, it works essentially like this: Depending upon the shotshell load involved, with smokeless powders, for every inch of barrel beyond 20" out to 40", about 4 fps is gained at the muzzle. Therefore, a modern load developing a muzzle velocity of, say, 1,200 fps at the muzzle in a 20" barrel probably would develop something like 1,280 fps at the muzzle in a 40" barrel."

"Periodically, a reader will contact me concerning achieving maximum velocities who is worried that his 26"-barreled double (which many ruffed grouse and woodcock hunters love) is not long enough. Having heard that shorter barrels do not develop muzzle velocities with a given load as high as longer barrels do, these individuals worry that they ought to have 30" or 32" barrels or 28" at the shortest. Well, given the above ballistic fact, the difference in muzzle velocities between a 26" and 32" barrel would be at most about 25 fps at the muzzle. But note: This difference will diminish rapidly downrange."

"All things being equal and, because of the physics of balls, pellets emerging from a longer barrel producing a higher muzzle velocity will slow faster than the same pellets would coming slower out of a shorter barrel. Because of this and by the time the pellets reach 25 yards or so, the 25-fps difference that existed between the two at the muzzle would become virtually negligible."

"Last, for any given load and barrel length, the tighter the choke, the higher the velocity will be that is produced at the muzzle. Full chokes can produce muzzle velocities that are 30 fps or higher than those produced by IC chokes. So if your target or hunting barrel does not match the choke constrictions listed for the shot types for the test barrels above, you are getting slightly higher or lower velocities than those listed on the factory boxes or in the reloading data. But again, all of these muzzle-velocity differences are minor, so no worries."

"In the final analysis, the principal importance of barrel length is to provide the length of sighting plane and gun weight/balance point that works best for each shooter. Longer barrels are more desirable for longer-range shooting—not, as we now know, for any ballistic reason but rather because such barrels provide weight-forward dynamics that greatly assist in keeping the guns swinging on crossing and overhead shots. Such is not necessary in upland hunting, where the predominant targets are typically close range and simple variations of going-away shots."

"And there you have the long and short of it."

 

That is an interesting write-up. Do we know who the author is, and what evidence he bases his statements on?
Not that I disagree with his position, because I don't, just curious.

 

Tom Roster

"Tom Roster is an independent ballistics consultant and author specializing in the design and testing of shotshells."

 

Thanks for pointing out it doesn’t matter to you, either. I’ll respond where I want to, though.