Page 1 of 4
The Applications of different twist rates
Posted: Sat Jul 25, 2015 3:36 pm
by vikkz
Hi Please can someone explain the best twist rate and the worst to have on a long range target rife.
This would be used for over 1000 yards
Re: The Applications of different twist rates
Posted: Sat Jul 25, 2015 3:40 pm
by WelshShooter
Twist rate depends on what calibre you're using and what bullet weights you intend to use. For 223 you'll need a 1:8" twist if you want to use the 77gr bullets and 1:12" for 308 to use 168gr bullets. I have a 1:8,5" twist on my 6.5 and there good for up to 140gr bullets.
Re: The Applications of different twist rates
Posted: Sat Jul 25, 2015 8:46 pm
by ovenpaa
It is also dependant on bullet length as well as weight, you will need a faster twist to stabilise longer bullets.
Re: The Applications of different twist rates
Posted: Sat Jul 25, 2015 9:57 pm
by IainWR
The Match Rifle community routinely use 1:10" with heavy 7.62 bullets for 1200 yds
Re: The Applications of different twist rates
Posted: Sun Jul 26, 2015 6:45 am
by Marmite5
Do you need a shorter twist for heavier bullets as a general rule?
Re: The Applications of different twist rates
Posted: Sun Jul 26, 2015 7:40 am
by ovenpaa
The twist number denotes the number of inches for the rifling to make one full revolution and yes a shorter/faster twist is usually preferable for heavier bullets conventionally produced bullets.
Re: The Applications of different twist rates
Posted: Sun Jul 26, 2015 9:24 am
by Mattnall
The Greenhill Formula has no mention of weight, it assumes a uniformly dense projectile but works quite well with the variable density of modern jacketed and composite bullets.
It is true that most bullets of a given calibre get longer as they get heavier, but tracer are longer and lighter than many of their FMJ/solid contemporaries and will require a faster twist than an FMJ of the same weight. That is why a 63gn 5.56 tracer will need a twist rate similar to an 80gn 5.56 match bullet to stabilise (and the much shorter 63gn FMJ stabilise just great in the fast twist the military use).
Re: The Applications of different twist rates
Posted: Sun Jul 26, 2015 4:55 pm
by Marmite5
Thanks
Re: The Applications of different twist rates
Posted: Tue Jul 28, 2015 9:53 am
by vikkz
Many Thanks for the very useful information,The rifle i have been looking at is the MODEL 700™ XCR™ TACTICAL LONG RANGE but is has a 1'/12 twist and I have been told this is no good for heavier bullets I am trying to shoot to ranges over 1000 yards.Can anyone suggest a good rifle system to do this .
Re: The Applications of different twist rates
Posted: Tue Jul 28, 2015 10:58 am
by Ian
Greenhill is a little dated, try the Miller:
https://en.wikipedia.org/wiki/Miller_twist_rule
Have a hunt around, there are various other formulae and approaches but none really have a definitive answer.