Ballistics question

[audiopro74]

Watching how its made, they're at the ul labs testing.

Testing a piece of bulletproof glass. Shoot at it with a .44. Distance of 15 feet. Approximately 15" barrel. He states that 15 feet is the optimal distance. He states that at that distance the slug is moving its fastest. Said it is still accelerating up till that point. It seems to me that it would stop gaining speed as soon as it left the barrel??

[LCU1670]

I guess it still accelerates for a bit.

[G-forceJunkie]

False, it stop accelerating the second the gas behind it stops.

[mrkubota]

plausible, the gas behind the bullet doesn't stop just because the bullet left the barrel. If you look at slow motion video, there's a column of air that preceeds the exit of the projectile as well.
Slow magnum powders usually continue to burn well after the bullet exits.

You can see the effect in this photo of my 500s&w:

[russ69]

I guess it still accelerates for a bit.

15 feet is probably max measured velocity because if you get closer the gun blast messes up the data through the sky screens. Max velocity is directly at the end of the muzzle.

[NytWolf]

If it continues accelerating for 15 feet, a 3.5-inch handgun and a 5-inch handgun should have no difference in ballistics. Also, rifle manufacturers would be stupid to offer bolt action hunting rifles in 22-inch, 24-inch, and 26-inch barrel lengths.

[mrkubota]

the expanding gas column still has mass that could influence the projectile.
IIRC, there was some early experimentation done to propel spacecraft with a series of explosive impulses. (no 'barrel' involved at all)

[NytWolf]

the expanding gas column still has mass that could influence the projectile.
IIRC, there was some early experimentation done to propel spacecraft with a series of explosive impulses. (no 'barrel' involved at all)

I would imagine it's not exactly the same thing. The bullet, in its path of travel, does not have more explosions to increase its velocity. The propulsion source happens once and only once.

[dieselpower]

False, it stop accelerating the second the gas behind it stops.

You'd think since Newtons law suggests this, but the speed in which the pressure wave is moving the bullet doesn't stop the second it clears the barrel, the inertia still gains for a few milliseconds afterward which translates to a few feet. You can prove this by setting a chrono a few feet from where you normally do and see a slight rise depending on how good your set up is.

I think 15 feet is a overstatement, I think like 3 feet is accuracy. If I was to guess I think someone is confusing 3 yards, 3 feet, 15 feet and 1 yard. I bet they test at 1 yard or 3 feet away for maximum velocity.