Originally Posted by CourierDriver
Remember the barrel length has a lot to do with feet per second and distance....short barrels fps slows way down, cant burn all the powder off...
I do believe most of the powder is burnt in the first inch or so--if you don't have flame coming out of the cylinder gap, then it's completely combusted. If you have flame come out of the muzzle, ok then you've got a point.
A longer barrel allows the hot expanding gasses more time to push against the bullet thus increasing its speed. I'm not sure where the tipping point is, I believe for 22LR its around 16 inches or so when longer becomes a detriment, but I'm guessing every caliber and every powder choice is probably going to be different. All the 38spl's I've shot I've assumed have had the powder combusted probably before the bullet moves; I think the 158 +P's are the same. Now I did recently shoot some Remington 125grn +P's and those had some flame out the cylinder gap, so the lighter bullet moved faster, plus I suspect that may have had some slower burning powder.