The Myth of Barrel Length and Velocity Loss

I have seen 100fps difference in three guns of the same barrel length and caliber, shooting the same ammo. its not common, but it happens.
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Seen that too. I've seen 20" barrels shoot slightly faster than 22" barrels and I've seen 100 fps difference with the same gun, with the same ammo when they were fired at extreme temperature ranges.

But not this. 2800 fps with a 180 gr bullet is a hot load in a 30-06. Remington factory 308 loads are not hot loaded.

Some guns certainly shoot faster than others, but it is the rare gun that actually reaches published ballistics with most being slower. I've NEVER seen a gun shoot factory loads 200 fps faster than the published balliatics. I wouldn't be surprised to see one 100-150 fps. slower, while another actually matched the published numbers though.
 
26 2826
24 2722 104
22 2713 9
20 2677 36
18 2654 23
16 2552 102

Average change = 55 fps or 27.5 fps/inch

As far as the cited article goes, a good experiment analyzes the data and then draws conclusions from it.

Beware of articles that have an obvious point of view they want to propound, especially ones that don't cite their data.
 
2800fps 180gr is a hot load for a .30-06, from a 22" barrel! The given .308 speed was from a 26" barrel. Given the long barrel, and a fast gun, I don't see it as impossible. However its more believeable with a 150gr bullet, and if there is any error in the data, I would think it was giving the wrong bullet weight.

However, I am not doubting the data as presented. It is quite possible, if not within the usual averages.

Again let me emphasize that published veliocities are only 100% representative of what the factory got with their test gun and ammo. And lots of times, they don't list the barrel length used for the test.

Factory loads are a good guide for general velocities, but your individual gun(s) can vary widely.

What this example shows us is, that some velocity loss happens when your shorten the barrel. How much change is not constant per inch in this test. In another test with different ammo and gun, it might be consistant per inch, or it might not be.

Assuming velocity loss per inch is constant, for all guns and ammo is, in my opinion, an error.
 
I observed a guy at our gun club shooting his 7mm MAG custom carbine. Barrel length was 20 inches. He produced a fire ball at the muzzle with every shot. Looked quite dangerous to me for hunting in the forest during a dry spell. So it goes.

Jack
 
With handguns, at least, it is possible to have higher velocities with a slower burning powder, in spite of the "inefficient" burning of the charge, meaning it continues to burn after the projectile is outside the barrel and "wasting" the powder. Faster burning powders may produce excess pressures in achieving the same velocities. While it is true that with a slow burning powder, there may be some waste, it is a case of efficiency being measured the wrong way, if velocity is what you're after and not economy of the propellant. But that's only with handguns.

I'm not at all sure that barrel length affects accuracy but it might affect the ease of aiming, again particularly with handguns. Everyone seems to use optical sights on rifles anymore, so it isn't a factor then.
 
The perfect length barrel is one that is long enough that your powder finishes burning just as the bullet leaves it. If the powder burns before the projectile exits, friction slows it down. If the powder doesn't completely burn, anything left over is wasted.
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Oversimplified to the point of being incorrect.

It is not about just powder burning, but pressure.

As long as the pressure behind the bullet is larger than friction losses the bullet will be accelerated by a longer barrel.
The powder finished burning long before that point.
The expanding high pressure gases can still do work.

Smokeless powder is almost uniformly under-oxidized.
There is not enough oxygen present to bring all the products generated to a stable cool state.
The muzzle flash is from the hot gases reacting with atmospheric oxygen.

'Flash suppressing' chemicals added to the powder are to provide more oxygen, but the down side is they reduce the energy density of the powder.
 
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