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2,696 Posts
Discussion Starter · #1 ·
i was sitting there at work eating lunch and had my calculator
handy.i came up with some interesting numbers.here goes.

V = velocity in fps.
R = rate of twist
RPM = revolutions per minute

V x 12
-------- = RPM

so lets take our doggin loads for example.they are running
right at 3400 fps. plus or minus about 20 fps, the twist
of my savage is 1 in 9.

so take the velocity and multiply it by 12 to convert it into
inches per second which comes to 40,800.then divide that
by R which is the rate of twist, it is a one in nine twist,
which means that every nine inches the bullet does one
complete revolution, that makes our new number 4533.333
revolutions per second. now multiply that by 60 to convert the number into revolutions per minute.
our new number is 272,000 rpm's

now if that isn't astounding enough check this.

M = mach
741.4549 = mach as described in miles per hour
5280 = feet per mile

V x 60 x 60
-------------- = mph

here we go.

again our loads are running at 3400 fps. so multiply by 60
to convert it into feet per minute, the number is 204,000
fpm, then multiply that by 60 again to convert it into feet per
hour that number is 12,240,000 feet per hour.
now divide that number by 5280 to convert it into miles per
hour, and we get 2318.18 mph.
now if we divide that number by 749.4549 you get the mach number which is 3.093 mach.

so out of our dog loads we have an object traveling at a little over three times the speed of sound, turning 272,000
revolutions per minute and is hot enough to be sterile.

it's amazing bullets stay together at all.

so if we run those numbers according to speer bullets
recommended maximum number.here is what i came up with.
they say not to exceed 3400 fps. with a one in ten twist.
so if you run the formula again you end up with the recommended maximum rpm's of 244,800 rpm's, our loads
are at 272,000 rpm's.
we are exceeding thier recommended maximum number
by 27,200 rpm's.
no wonder critters explode really violently.


Under appreciated
92,403 Posts
Great info.. and thanks for the calculations.

I cant wait!

2,672 Posts
Now can you figure head pressure/kinetic energy on specific rounds to see just what exactly is impacting?

17,011 Posts
:confused: ouch, even though i didn't do the work, it sure makes my head hurt

13,863 Posts
Some years back, The Varmint Hunter Magazine posted a page of the RPMs of most speeds, from a .22 Hornet to a Swift, and it was pretty amazing, still is, that the bullets hold together, shoot really, really well, and still do the job intended. I still intend to put a fast twist .22/250 together sometime, and shoot some 50s at about 3900fps, and go whack some rats (I'd use 40s, but the wind blows them around too much to suit me). I've seen rats hit with the 1-12 twist Savages, though, and it really flips them, often rotating them in the flips, pretty cool stuff. I think a 1/8 twist would be spectacular, and I could use 69s if the wind was really blowing, too. Ahh, I can see it now........:eek::hysterical:

3,898 Posts
I think the sound barrier is like 1200fps....is that correct? That is why some subsonic 22's don't have the crack sound.
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