Twist and velocity

[jericho]

Good morning all

So I was watching a CSI:NY episode last night and there one of the characters was going on about how the bullet in said victim did not have enough velocity 'cause home made weapon had no rifling so bullet just rattled down barrel.As far as I understood,in simple terms no rifling wont affect velocity? A good fit of bullet in barrel will have more of an impact? I understand that there is a relationship between weight(actually length) of bullet and twist.

Am I right or am I missing something.lightbulb

 

[MontanaRifleman]

Jericho,

Twist is basically detrmined by the cal-to-length relationship of the bullet. Velocity will have an impact as well. So basically, the longer the bullet in a particular cal, the tighter the twist required and the great the velocity, the less twist required.

-MR

 

[jericho]

Thats the one part I do understand. They were saying the absence of rifling is what decreased the velocity. I thought some of the older muskets( pre rifling) when packed and charged well gave comparable velocities to some modern day rifles.

 

[MontanaRifleman]

That is beyond my knowledge and understanding, so I cant help you there.

 

[J E Custom]

Thats the one part I do understand. They were saying the absence of rifling is what decreased the velocity. I thought some of the older muskets( pre rifling) when packed and charged well gave comparable velocities to some modern day rifles.

Remember this is TV.

My understanding of the theory is that if the bullet is a good fit it would be faster than if it
was not. But it would have more drag due to the increase in surface area slowing it down
a little. But a sabot with a good seal and of the same weight would be the fastest with
everything else being the same.

If a weapon was worn out and didn't have any rifling left it would have a lot of blow buy
and would be slower, But I have never seen a rifle with all of the rifling gone. I have looked
down the bore of rifles with over 75,000 rounds through them and they still had rifling
but 4 or 5" of throat was gone.

The old muskets used smaller round balls slightly smaller than the bore so they could be
patched with cloth or paper to seal the bullet to the bore and improve the loading process.

J E CUSTOM

 

[jericho]

I did fail to mention that said gun was a home made gun made out of some metal tube hidden in a pen. I never took it too seriously from the beginning. Its still an entertaining show though.

 

[trebark]

I had to stop watching CSI when I saw an episode where the victim was killed with a frozen beef bullet.

Yes, the criminal stuffed ground beef into bullet cast. Froze it, then loaded it into a cartridge. Then proceeded to keep the bullets frozen until moments before shooting the victim. It should be mentioned that the crime took place far from any building or electrical source (read: refrigeration).

So anytime someone says CSI...I say....Frozen Beef Bullets!

 

[Shootin4fun]

CSI is just entertainment. A lot of the technical statements they make are simply not correct or unrealistic.

As for velocity, I think they simply meant that the barrel was not a precision fit seal with the bullet.

And this was another borrowed or stolen idea by TV writers not smart enough to come up with ideas of their own. For all of us old enough to remember the movie "Day of the Jackel", the frozen bullet concept was first introduced there. Covert hit operation at the beginning showed the assailants removing frozen water bullets from a special carrying case, loading them up into automatic short barreled assault weapons and doing the hit at an embassy or CIA hideout or something. (sorry, its been 38 years) All of this is a dumb idea though...uh, just to cover up ballistics, you're going to go through all that, and then fire ammo that will probably fracture inside the magazine???? And then you leave brass everywhere?? An intriguing concept at the start, but that's about it.

I'm real "fun" (not) to watch movies with because I pick apart all the technical flaws and holes in the plot. Watched Mark Walberg in "Contraband", and it was somewhat entertaining but the plot had more holes than my 200 yard targets with 5 round groups. The studios must think we're all so stoned that we can't think above a 3rd grade level. Well, as they say, "That's show business!"

 

[BlackStreak]

Not saying this happens in every instance but a bullet can exit the muzzle with more velocity in a stouter twist barrel due to more resistance incountered. The increased resistance causes an increase in pressure behind the bullet as its pushed down the barrel. The increased pressure effects the burn rate of the powder and causes more of it to be burned faster. So says Bryan Litz in his Applied Ballistics book. I'm quite sure he does a better job of explaining it than what my futile attempt did. Its not substancial but it got my attention and enlightened me when I readit. Made perfect since to me.