BARREL TWIST&GROVE

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WHAT IS YHE LARGIST BULLET A 1&12 5 TWISTBARREL WOULD HANDLE IN 30CAL.?
 
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Probably a 180 gr Sierra MK. Some guys shoot 190's, depending on the cartridge. I think Lilja's website has a link to a twist calculator. You might look there or do a search for a rifling twist calculator. You will need the length of the bullet in question, the weight and the ogive profile, plus the the velocity on most calculators. You might also do a search for the Greenhill formula.
 

Steve Shelp

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Joined
May 3, 2001
Messages
351
Location
NC
Jerry's right. I've personally shot 200gr SMK, 210gr Berger's, 190gr JLKs, through a 12 twist 30" barrel chambered for 308 Baer. They all shot really well with those higher velocities.
We also shot 220gr SMKs with the original lot# of R22 when it first came out (much slower then today's R22 powder!!!) and they stabilized on our 400yd test range. But that load was really really hot. Never shot that again. Wrecked the cases doing it.

I don't have any experience with slower 308 Win or similar velocities in a 12 twist. Anyone with a Rem 700 Varmint Special should be able to tell you. Those barrels are 12 twist from the factory for the 168gr MK.
I wouldn't recommend the Greenhill formula. It's old and based on a drag function from bullet shaped/made 100yrs ago. With todays bullets it usually recommends a twist that is a 1 or more inches faster than needed for stabilization. That has been my experience with 6.5 -> 338 modern day boattial bullets anyway.

Steve

[ 07-30-2003: Message edited by: Steve Shelp ]
 

DANTEC

Well-Known Member
Joined
Jul 6, 2002
Messages
390
Location
France
try on line software as JBM ballistic they compute bullet stabilzation http://www.eskimo.com/~jbm/ballistics

basic is :
more you have velocity less you need fast pitch
less you have fast pitch more your rifle is accurate ( bullet unbalance effect )
less you have fast pitch less bullet distorsion you get
....

I have shoot 187 Scenar in 1 in 12 launch with 30.338 WIN
I shoot 175 SMK in 1 in 13 with a 300 WIN MAG

good shooting

DAN TEC
 

Mysticplayer

Well-Known Member
Joined
Jul 27, 2001
Messages
1,459
Sierra confirmed that in a 12 twist, a 200gr gameking or 190gr Matchking can be used. If you are using a cartridge large enough for 3000fps or higher, you may be able to get 200gr MK to work.

In something like a 308win, I would limit to the 175gr MK but a better bullet would be the 155gr Amax.

Jerry
 

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