twist rates and bullet weights

[unclebill]

i tried using the greehill formula but i am too stupid to grasp it easily.
is there a chart that will help me figure out a ballpark figure for various twist rates and bullet weights?
what i am really wanting to know is will a 310 gr. boolit work in a rifle with a 1-38 twist?
thanks
bill
__________________

[Pat I.]

Here's an online estimator.

http://www.nfa.ca/content/view/134/197/

[44man]

I use it, also the RD 265 gr.
But then again, there is not a bullet/boolit made that REALLY shoots from the stinking Marlin past 50 yd's. I don't know why they bothered to rifle the thing. I thought about putting a pipe wrench on the end and twisting it up. :mrgreen:

[Wayne Smith]

It is length, not weight that you put into the formula. Measure your bullet.

[montana_charlie]

what i am really wanting to know is will a 310 gr. boolit work in a rifle with a 1-38 twist?
Knowing the caliber you are working with is important when trying to answer your question. But, if you are talking about a .45, it should be about right.
CM

[longbow]

While I get disagreements, my experience is that my Marlin .44 mag. 1:38 twist does not like the 300 gr. boolits or bullets I have put through it. They become unstable at around 75 yards. I have gotten good accuracy up to about 265 gr. though at well past 100 yards.

RanchDog was doing some testing and doing very well at long range with his 265 and 300 gr. boolits in 1:38 twist and starbow says he gets good accuracy to at least 100 yards with WFN boolits and hot loads so boolit design and velocity likely comes into play here too.

Greenhills says 0.720" is the longest boolit that will stabilize in 1:38" twist (for .44 cal.). This is a guideline though so I do not dispute other's results.

Based on this if the 310 gr. boolit is a RanchDog design or WFN style it should work at least at the top end velocities. If your gun is .45 it may do better.

Longbow

[44man]

The Greenhill is so out of date it is useless and so far off as to be a waste of time. For one thing using the length of the boolit is wrong. The drive band length is what counts, not how long the nose is.
However if you put the drive band length of my 330 gr boolit into the Greenhill, I need 1 in 52". To get a .44 boolit right for Greenhill using a 1 in 20" twist, it has to be 1.35" long. For a 1 in 38", the boolit needs to be .730". Now we know it doesn't work with either. Also there is a stupid velocity range.
A heavy boolit in the Marlin with the 1 in 38 twist needs to be shot much faster then the gun and cartridge is capable of doing.
The only way to see what a twist needs is to shoot the darn thing with everything made and at every velocity the cartridge is capable of with each boolit.
Greenhill belongs in the trash can. [smilie=1:
Look at the twist rates of the most accurate guns made for heavy boolits--the BFR's.
Desert Eagle .44---1 in 18"
.460---1 in 20"
.500 S&W and .50 Action Express--1 in 15"
.475---1 in 15"
45-70--- 1 in 14"
.454---1 in 20"
Even the lowly Ruger .45 has a 1 in 16" twist.
The standard for the .44 is 1 in 20". For the added velocity of the Marlin .44, even a 1 in 22" rate would work. But take note that because of complaints, they changed the .444 to 1 in 20". Even it was not capable of driving a heavy boolit fast enough.

[joeb33050]

Greenhill tells us that:
a .429" bullet, 38" twist, max. bullet length = .726"
my estimator of max. wt. = 246 grains

a 30"twist .429" bullet stabilizes a bullet .920" long, max.
my estimator of max. wt. = 312 gr.

the book contains a workbook that allows one to calculate twist, bullet length, bullet dia., bullet wt.---enter some, get the rest.

Greenhill is an excellent estimator of the twist/dia/bullet length relationship, for all reasonable = commonjly shot velocities, at ranges to 200-500 yards. Slow bullets at long range seem to need faster-than-greenhill twists. Greenhill is right, the detractors are wrong.

"Cast Bullets For Beginner And Expert", Second Edition, can be found and read online at: http://sports.groups.yahoo.com/group/CB-BOOK/
The book is in "FILES", the Table Of Contents is in "The Beginning"
See Chapter 2.3 TWIST

joe b.

[405]

Here's another twist table that is easy to use.... also has some explanation

http://www.montanabulletworks.com/wst_page11.html

[Firebird]

That's a good article, all of these methods are just ESTIMATORS, they don't give exact results. The exact results depend on the center of gravity and moments of inertia of the bullet, which is physics talk for saying "shape", and the rpm the bullet spins at. Velocity and twist determine the rpm, but shape can only be generalized, so you end up with an estimate, not an exact result. And since the Greenhills formula is from the 1800's, it was designed to estimate for round nose bullets at 1400 fps, not todays long pointed spitzers at 3000+ fps. The surprising thing is that it comes as close as it does; the higher velocity gives a higher RPM, which compensates pretty closely for the long pointed shape.

[unclebill]

my original question was badly phrased.
i am sorry it wasnt clearer.





.45 l.c.
and since i can never remember the chain of (to me)nonsensical numbers that signify a certain boolit mold here is a pic.
308 gr.
http://i98.photobucket.com/albums/l272/billhedges/zsmithwesson27-2-30.jpg

BTW
the rifle is a henry big boy.

[unclebill]

i have about 10 different kinds of boolits that village idjit was kind enough to make me.
but i cant remember the string of numbers for each one.

[joeb33050]

i tried using the greehill formula but i am too stupid to grasp it easily.
is there a chart that will help me figure out a ballpark figure for various twist rates and bullet weights?
what i am really wanting to know is will a 310 gr. boolit work in a rifle with a 1-38 twist?
thanks
bill
__________________

Greenhill: .454" bullet, 38" twist, max. bullet length = .814", my estimator of bullet wt. is 309 gr.

Thus, Greenhill says a 310 grain .454" bullet with 38" twist is on the ragged edge os stability. Everything has to be right.
Remember, for any given twist/bullet combo, better stability comes with higher velocity, higher air temp., higher altitude, lower barometric pressure and denser bullet aloy = less tin/antimony in the mix. Be safe! If 310 gr. doesn't work, go to a shorter bullet.
joe b.

[joeb33050]

Here's another twist table that is easy to use.... also has some explanation

http://www.montanabulletworks.com/wst_page11.html

Interesting. The tables are copied from "Cast Bullets For Beginner And Expert", Second Edition.

No copyright, no foul; but I'd expect attribution.
joe b.