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6.5CM Twist Rate & Barrel Length

Cardboard Assassin

Gunny Sergeant
Full Member
Minuteman
Dec 6, 2020
594
353
Canada
I'm pretty sure its time to swap my 6.5CM barrel (round count is up there and accuracy has dropped off a cliff)

The original barrel is a 1:8 twist and I have had good luck with various 140gr bullets but I have some heavier bullets so was wondering if I should go for a 1:7.5 twist.

I ran the numbers on the Berger calculator and it looked like the 1:7.5 would work best for the range of bullets I have (139 gr Lapuas / 140gr ELD-Ms / 144 gr Lapuas / 150gr Sierras).

With this in mind is there any reason not to go with the 1:7.5 twist? Will the accuracy of the lighter 139gr / 140gr bullets be affected by the switch from 1:8 to 1:7.5?

What is preferred barrel length for 6.5CM? I have a 24" right now which has served me well but its a slow barrel for sure (it ran best at 2650 FPS), from what I have read it seems 26" seems like a popular option and should take me to the ~2700 FPS which is more typical for 6.5CM.

Thoughts?
 
I just ordered a 8.5-7.5 Bartlein, I have had 8 twist and also 7 twist barrels. If you are going to run the heavy bullets go faster if not an 8 will be fine.