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.