disintegrating bullets

[Dougan]

Having read about this phenomena in another thread, where a bullet pushed at a high velocity can break up after a few hundred meters of flight, I have a few questions...

What are the maximum velocities being achieved by civilian shooters? - and at what point do the laws of physics prevent more, and for what reasons? (not encouraging 'pushing the limits'...just curious)

What are the actual reasons for a bullet to break up, and is it mainly lighter bullets...or can this happen with 140-200 gn bullets?

[kennyc]

as far as I am aware, the bullets disintegrate when the rotational forces exceed their ability to stay together, that would probably be more a problem with very light for calibre bullets being used in very tight twist barrels, isn't this one of the limiting factors in maximum useful muzzle velocity's?

[Dougan]

So like centrifugal force!? - so how fast do bullets rotate? (typical weights and twists)

I know I could research this online...but if anyone knows the numbers (revs per second?) of hand...?

[ovenpaa]

Bullet RPM = MV X 720/Twist Rate (in inches) so:

3300x720/8 = 297,000 RPM or quite a lot. Consider as an alternative a .308 with a 1:12 barrel at 2800fps is 168,00RPM

[Dougan]

Ok, I'm trying to get my head around that - I can see how fast that is (!), and the difference lighter bullets make...

...excuse me being thick, but where does the '720' come from in the equation?

[ovenpaa]

MV x (12/twist rate in inches) x 60 = Bullet RPM

[Dougan]

MV x (12/twist rate in inches) x 60 = Bullet RPM

Ok that I get - so does a lower twist rate increase the RPM?...I would have thought the opposite! (my head is starting to hurt :lol: )

[ovenpaa]

a lower number twist rate such as 1:8 will give a higher RPM than a higher number such as 1:12 for the same MV

[Dougan]

Ok, now I am really being thick ( ) - though I think the penny has finally dropped....1:8 is 1 turn in 8" (yes?) and therefore a tighter/quicker twist than 1:12...which is 1 turn in 12" (yes?)...

...for some reason (i think from TR rifles) I've got the impression that the bigger the first number is, the tighter the twist is ( i.e a 14:1 is tighter than 10:1) - this is because I know that 14:1 is better for shorter range (TR 155/.308), and 10:1 is better for long range...but I've had it the wrong way round (shouldn't be admitting to this online :roll: ), as I've assumed that tighter twists stabilise a bullet sooner...so better for short range...?

I think I need to read up on this stuff...anyone recommend a good book?...preferably in 'layman's terms'.....

[ovenpaa]

Bryan Litz - Applied Ballistics For Long Range Shooting would be a good one to start with. Look for a used copy of the first edition as opposed to a new copy of the latest edition and you should save yourself about GBP35