ORIGINAL: CZ2506
ORIGINAL: eldeguello
As a rule of thumb, we say that a standard round such as the .308 would lose about 25 feet per second for each inch cut off a barrel like yours.
Would the loss of velocity be noticeably different for cartridges that work best with slower burning powders? for instance the 300 mags or 25-06 rem?
Well, the final MV of that type of cartridge might be less becausethose big charges require longer to accelerate their bullets. So you might lose more MV when you cut them off, say 35-50 FPS/inch of barrel cut off.
Butwhen speaking only of the type of powder which is best,the slower powders will still produce more MV. For example, IFyou get the maximum possible velocity from a given cartridge and rifle using a slow powder likeH4831 with a 26" barrel, if you cut that gun to 20", your NEW (lower)maximumpossible MV will still come from that same amount of that same powder.
Many people think that to get the highest velocity from a given cartridge with a shorter barrel, they should use a faster powder. The idea is that "more of the faster powder burns in the short barrel. Sounds logical. However, what actually happens when you fire the gun is that ALL of the powder, regardless of type, is completely burned up by the time the bullet has travelled 3" to 5" up the bore. In order to get a higher velocity from a faster powder, you would have to load it to HIGHER PRESSURES, and this is a very limited option-limited by the strength of the brass cartridge case and the structure of the gun!
The slower powder, on the other hand, has to be usedlarger amounts to produce the higher velocities,but it reaches a peak pressure within safety limits which LASTS LONGER, thus applying MORE PUSH to the bullet for a longer period of time until the bullet exits the muzzle. Faster powders, even if loaded to higher peak pressures, drop off in pressure much more dramatically, thus pushing the bullet for a much shorter period of time and consequently achieving a lower final velocity at the muzzle.