Thread: Projectile vs barrel length

.308 Win Barrel Cut-Down Test: Velocity vs. Barrel Length « Daily Bulletin
If what you're saying was true, the above experiment would not have documented a 261fts drop in mv when they sawed off the barrel from 28" all the way down to 16". They average was a loss of 22.5fts loss per inch
So, the powder ain't burning past 3 or 4 inches but that really is semantics. The bullet is still accelerating all the way up so a shorter barrel does leak a crap load of wasted 'expanding gas' shall we call it.
Your post did make me go looking and a lot of guys find unburnt powder but that's due to the oxygen being depleted apparently and nothing to do with barrel length