barrel twist question

[atlatl]

I am having a 6 mm AI made primarily for shooting steel plates at 500-600 yards for my own enjoyment, and for use as a sporter weight varminter. I will likely use bullets from 70gr to 107gr and was planning on ordering an 8 twist barrel- the barrel maker suggested a 9 twist. I could order an 8.5 twist as a compromise. The rifle will have a 24" barrel as it will be used as a "walking varminter".

I would appreciate others input on selecting a twist rate, I would like to know approximately how much accuracy and velocity I may sacrifice by using the fast twist barrel with lighter bullets. Thank you.

 

[Larryh128]

I think that your barrelmaker sounds pretty much spot on. You can over rotate varmint bullets to the point that they won't get to the target. Ask me how I know. The 70 gr bullets would probably be better in a 1-11 or 1-12 twist.

 

[bsc4444]

I have a Cooper in 6br with a 1:8 twist. It shoots Sierra 70 gr match bthp [#1550] in little bitty holes. Loves 30.3 gr H 322 cci br4 lapua brass
jumped .007 I would not be afraid of the 1:8 if you want to shoot up to 107 gr-ers.

 

[Grimstod]

The bullet would only fly apart if you have both a fast twist and fast bullet.
Take a 8twist barrel and put a bullet through it at 2000fps
Then take a 8twist barrel and put a bulletithrough it at 4000fps the bullet will twist twice as many times per second.
Rifle twist is a combination of FPS and turns per inches. Read Krigers website for a complete explanation.

 

[shortgrass]

Someone said, "there's no free lunch". It'll be a compromise if you make a build that'll "do everything". If the 6mm AI is what I'm thinking, the Ackley version of the 6mm Rem.,,,,,, you've got a big ol' case, best use of it is a "big ol' bullet". Mine has a 7 twist for the 107-115g. A very effective LR round.

 

[atlatl]

Thank you BSC444, that was what I was hoping to find out. I should have asked : for those members who have 8 twist barrels on high velocity 6mms, what sort of results do you get with lighter bullets. I will get the 8 twist barrel as I know I will shoot 105s and 107s frequently, I just wanted to know what kind of results I might expect with 70s and 75s. Thank you.

 

[3Ackleys]

I Have a 243 AI w/ a 9 twist. I shoot the 105 gr Berger vld hunting bullets.
They shoot so good I use them for everything