Trent, I'm not sure I agree with you about how fast pistol powder it. If it all burned up within the first inch or so, why do you still get muzzle flash at night? why would you get more muzzle velocity out of a longer barrel than a shorter one? (ex: 38spl out of a rifle barrel vs a pistol)
You get muzzle flash on handguns because the powder is still under incredible pressures, it's a very hot, very high pressure gas. Bullseye, Unique, etc will be fully burnt by the time the bullet is out of a 1.5" barrel.
A charge of Unique in 38 special shot out of a 3" barrel is going to have a heck of a lot more flash than a rifle, because the gas is still under tremendous pressure at the time it exits the muzzle, compared to a 16" rifle. The gas pressure on a rifle has dropped MASSIVELY by the time that bullet exits the muzzle. Now, switch to a slower burning powder like Blue Dot, and you'll see something entirely different; traces (streaks) of unburnt powder out of the 3" barrel, and a bigger flash out of the 16" barrel.
Slower burning pistol powders on shorter barreled guns will show streaks (sometimes visible in daylight) which is powder still burning. Blue Dot and 3N38, for instance, will show nifty little "traces" when shot from 3" or shorter barrels - THAT is powder that's still burning. A little more impressive at night.
On larger magnum rifles, particularly 50 BMG, this effect is even more pronounced and the streaks burn longer. (I can see them very clearly in daylight when shooting my DShK, just as you see in the photo below, taken over in Syria):
