Thread: Myth? - shorter barrel = use faster powder?

I think it's a bit different to what is described. You are trying to get to max safe pressure, and maintain that pressure in order to achieve the most force and thus acceleration on the projectile. As the powder burns, the projectile starts moving.

This means powder is changing from solid to gas as the projectile is going down the barrel.

Heavier projectile means slower acceleration. That means that the area for the gas to expand into is increasing slower than with a faster moving projectile. Do you are balancing the rate of press increase from expanding gas, with the rate of increase of the area ,(barrel and chamber) is increasing.

Shorter barrel means there is less time for the expanding gas to push the projectile. Theoretically, a faster burning powder means that max safe pressure is reached sooner, so that the projectile experiences that force for max duration. The flip side is, that the powder stops turning to an increasing volume of gas sooner. That means that pressure will drop earlier due to expanding area.

I think the theoretical best is max safe pressure instantaneously, which then expands at the exact rate to maintain that pressure as the area increases due to the projectile moving down the barrel.

You also want all combustion to be complete before projectile leaves the barrel so you dont get an obnoxious muzzle flash, and waste energy (inefficient use of powder)

[QUOTE=Danger Mouse;1194280]

Heavier projectile means slower acceleration. [QUOTE]

Not in practice i have found. See you stuff anything into the spare void in a case (be it more projectile or whatever) you get more pressure.
For example, try eld 140gn with 46gn of 2213. You will get say 2760fts. Use the same setup but swap in 147gn eldm's and you will get 2800fts from the additional pressure.

I have my chamber set up so that my lands still allow a regular 140 to have all the bearing surface of the neck touching bullet. The 147s end up down deeper into the case (just touching powder)