Rate of twist??

D

DaveC

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Barnes sent me the reloading data for the .270WSM. I told them I have a Savage 16FCSS and was looking to reload the 140 gr TSX. They said that they recommend around 110gr TSXs for 1 in 11" twist barrels. 140gr TSX bullets might not stabalize in my barrel.

Can anyone explain this to me? Is that just the TSX? Is that due to the length of them, or what? I shot 130gr and 140 gr factory loads and they were fine.

I want to use a sturdy bullet like the TSX and be able to use the .270 WSM for deer, elk, moose and black bear.

Any comments????
 
Might have to do with aerodynamics of the bullet. Supersonic objects produce shocwaves from their leading edge back. Those can shift the center of presure and cause an unstable situation. Or they're covering themselves and don't want you trying the heavier bullets and-if they don't perform well- telling everyone what crap TSX's are... :rolleyes:
 
Greenhill formula (from the turn of the last century) might shed some light : twist = 150 * d * d / L where d and L are diameter and length in inches, respectively.

The assumption is the bullet is round point and made of lead, so the weight (actually the density) was more or less accounted for back then. Lighter jacket material, hollowing, etc. will skew the result.

I don't know for sure what the length of the 110 TSX is, but assuming
1. the length of the 140 is in proportion to the weight
2. the 140 is 140/110 = 1.27 times longer than the 110
3. the ideal twist for 110 is 1:11
4. twist is inversely proportional to length according to the formula

then a better twist for 140 may be 11/1.27 = 8.6 ==> 1:9 but results vary gun to gun
 
"...explain this to me?..." The TSX is solid copper. Copper isn't as dense as a regular, lead core, copper jacketed, bullet. It'll fly differently. It's also why you need to use data from Barnes for their bullets.
 
I have always found the Greenhill formula worked well for me when using solid base bullets. When buying a barrel, I chose one that is 1" faster than the formula recommended. Also found that hollow base bullets can be stabilized with a much slower twist than the formula suggests.

cheers mooncoon
 
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Barnes sent me the reloading data for the .270WSM. I told them I have a Savage 16FCSS and was looking to reload the 140 gr TSX. They said that they recommend around 110gr TSXs for 1 in 11" twist barrels. 140gr TSX bullets might not stabalize in my barrel.

Can anyone explain this to me? Is that just the TSX? Is that due to the length of them, or what? I shot 130gr and 140 gr factory loads and they were fine.

I want to use a sturdy bullet like the TSX and be able to use the .270 WSM for deer, elk, moose and black bear.

Any comments????
Click to expand...

Hi DaveC, I made a few months ago a bullet twist rate calculator It can surely Be useful for you .... The only thing you need is the Lenght of the bullet and the diameter of the bullet...

here is the links you can download the file

http://www.mediafire.com/?1fmdy1tspgw
 
A pure copper bullet will always be longer that a lead cored one of the same weight.Hence a longer bearing surface in the bullet jacket.this may cause keyholing if not driven fast enough in some twists.............Harold
 
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