Barrel Length and Muzzle Velocity

Tony and anyone else who may know,

I have heard that you lose the 100fps per inch also but I am wondering if that is a generalization that is an estimate and not always true. With that number one could guess that a 24 inch barrel is only capable of 2400 fps which is not true. So much depends on the weight of the bullet and the type of powder and primer. I have also heard that for example a shotgun slug shell burns most all its powder in the first 16 inches. This is specifically because there are 18 to 24 inch slug barrels readily available. Once the powder has completed its burn, would not any excess barrel actually slow the bullet down do to friction? Though the 20 inch barrel on the 30-30 for example may not be capable of the same top velocity as the 24, with the proper loads for that length, couldn't you under normal circumstances expect to be able to find the performance that is needed? I am not a expert by any means and just wondered what the true case may be.

Ed,

you are right, there are no hard rules in this (or most other things).

In fact, the powder is burnt during the first few inches of bullet travel even with the biggest magnums and slowest powders. But even after that, the pressure continues to accelerate the bullet. In some point the friction overcomes the pressure and the bullet starts to slow down. This does not often happen in rifles (so much powder), shotguns (so little friction) or handguns (so short barrels), but it does happen in 22LR rifles, where maximum velocity with standard ammo comes from about 16' barrel, and in pistol-caliber carbines with fast-burning pistol powdered ammo.

30-30, with its modest pressure and small charges, is ok in a 20' barrel, but a 300 Mag, for example, would gain velocity with every extra inch up to somewhere not very practical...30'? Again, this depends very much on the powder used. For example Speer and Sierra manuals have same calibers in both rifle and pistol, and the best loads are often with different powders. Speer also lists tried velocity variations with different barrel lenghts for some calibers. That is the way to do it!

Some time within the last year I read of an experiment about this. Starting with a 28' the barrel was cut 1' at a time after chronoing a group. The velocity loss was around 25fps per inch down to the point that there was some unburned powder coming out the muzzle. At that point there was around a 100+fps loss. Then after that point the change was less again. AIR the break point came at around 19-20 inches.

Bill Van Houten (USA Ret)

Nothing that is politicaly Right can be Moraly wrong.