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Twist rate = Grain
- Thread starter the blur
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LaHunter
Well-Known Member
you can do a search on here, or just a google search. The twist rate needed to stabilize your bullet in flight is going to be dependent on your caliber, bullet, bullet wt, and muzzle velocity. The elevation plays a role in the needed twist rate, but less than the other factors listed.
I believe Berger has the needed twist rates for their bullets you can check out. This may or may not be relevant to you if you aren't shooting Bergers, but it can give you a starting point.
I believe Berger has the needed twist rates for their bullets you can check out. This may or may not be relevant to you if you aren't shooting Bergers, but it can give you a starting point.
twist rate needs are determined mostly by the "length" of the bullets bearing surface not necessarily the weight.
yankee outlaw
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easy button berger twist rate
entoptics
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Berger Stability Calculator
bergerbullets.com
JBM Stability Calculator
www.jbmballistics.com
You'll need some measurements for the JBM calculator, but Google should provide those for you with a little searching. JBM can also account for plastic tips, which Berger does not.
Twist Rate Stability Calculator
Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.
bergerbullets.com
JBM Stability Calculator
JBM - Calculations - Stability
You'll need some measurements for the JBM calculator, but Google should provide those for you with a little searching. JBM can also account for plastic tips, which Berger does not.
Hugnot
Well-Known Member
Overall length of bullet, like from base to tip but subtract length plastic tips. Goto JBM - there are other bullets than the spendy Bergers.
For example:
These are some common .308 Hornady hunting bullets that would work in a 12 twist .308, except the pointy 165 Nosler RDF. 12 twist, that would have marginal stability at cold heavy air. I ran the Sg program using 35 deg F because I thought this would be common for shooting deers & such at colder hunting season temps. Should you shoot the deers at high elevations decrease the pressure. Temperature & pressure have minor effects on Sg compared with twist rate & length. Most .308 hunting rifles are intended for use under 300 yards so I skipped heavier & real pointy match bullets. A .308, 150 grain bullet at almost 2900 fps mv kills deers real good. Some bullets might have marginal Sg values & fail to have adequate stability under certain conditions, like cold heavy air. I like the .308 150 SST for shooting deers & under and have had real good results on long range rodents using it in a .308 W.
The twist rate of the Tika must be known - from manufacturers stats or by measuring it.
Tape measure, tape, felt tip pen, cleaning rod with lightly lubricated tight fitting patch. Place a strip of tape on back end of cleaning rod, draw line on tape with felt tip, run rod with tight patch into bore, mark reference point on tape with selected feature on rifle, pull back rod & stop when line on tape has made 1 revolution, measure distance between 1st reference point & second reference point (common to same feature on receiver.
Hammer forged rifling is consistent from bore to bore. Button rifling may vary. Stats might be incorrect. Verify is good. Don't buy lots of bullet that won't shoot good (inadequate stability, like under Sg 1.4)
The Miller stability, or Sg calculator, is used by JBM & Berger. For a more definitive approach look at:
www.hornady.com
For example:
These are some common .308 Hornady hunting bullets that would work in a 12 twist .308, except the pointy 165 Nosler RDF. 12 twist, that would have marginal stability at cold heavy air. I ran the Sg program using 35 deg F because I thought this would be common for shooting deers & such at colder hunting season temps. Should you shoot the deers at high elevations decrease the pressure. Temperature & pressure have minor effects on Sg compared with twist rate & length. Most .308 hunting rifles are intended for use under 300 yards so I skipped heavier & real pointy match bullets. A .308, 150 grain bullet at almost 2900 fps mv kills deers real good. Some bullets might have marginal Sg values & fail to have adequate stability under certain conditions, like cold heavy air. I like the .308 150 SST for shooting deers & under and have had real good results on long range rodents using it in a .308 W.
The twist rate of the Tika must be known - from manufacturers stats or by measuring it.
Tape measure, tape, felt tip pen, cleaning rod with lightly lubricated tight fitting patch. Place a strip of tape on back end of cleaning rod, draw line on tape with felt tip, run rod with tight patch into bore, mark reference point on tape with selected feature on rifle, pull back rod & stop when line on tape has made 1 revolution, measure distance between 1st reference point & second reference point (common to same feature on receiver.
Hammer forged rifling is consistent from bore to bore. Button rifling may vary. Stats might be incorrect. Verify is good. Don't buy lots of bullet that won't shoot good (inadequate stability, like under Sg 1.4)
The Miller stability, or Sg calculator, is used by JBM & Berger. For a more definitive approach look at:
Ballistic Calculators - Hornady Manufacturing, Inc
Kestrel® 5700 Ballistics Weather Meter with Hornady® 4DOF® Combining complete onsite environmental measurements with the precise trajectory solutions of the integrated Hornady 4DOF® ballistics solver, this rugged all-in-one...
Last edited:
Varmint Hunter
Well-Known Member
I believe most (possibly all) of the Tikka rifles in .308Win have a 1/11 twist. You should be good to go with any bullet up to 180gr.
Doom2
Well-Known Member
JBM also has a catalog of bullet lengths. Neither the Greenhill or Miller formula are accurate as they tend to overestimate the required twist. I believe Berger is using the Gyroscopic Stability equation for their estimate which is a more complex formulation.Berger Stability Calculator
Twist Rate Stability Calculator
Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.
JBM Stability Calculator
JBM - Calculations - Stability
You'll need some measurements for the JBM calculator, but Google should provide those for you with a little searching. JBM can also account for plastic tips, which Berger does not.
The twist is a function of the overall length of the bullet. For a fixed bore diameter the weight increases the length for similar bullet geometry.
