260 Twist Rate

[chadjamesr]

I'm building a .260 and I have a problem. I wanted an 8 twist 5R 6.5mm Bartlein barrel, but it is an 8 month wait to get one from Bartlein.

I've found a store that has a shipment coming from Bartlein in a couple of weeks but they only have the 8.5 twist.

I plan on shooting everything from the 120gr to 140gr bullets. Should I wait for the 8 twist barrel or will the 8.5 twist be fine.

Has anyone had bad luck with the 8.5 twist barrel and 140gr bullets?

Does anyone know a place where they have the 8 twist barrels in stock?

Thanks,

Chad

 

[Laurie]

Chad,

1-8.5" is widely used with the 6.5s, some people prefer it in fact. The 142gn Sierra (1.375" length) is computed to have a stability factor of 1.5 at 2,800 fps in 'standard conditions', and a bit over 1.4 at 32 degrees F.

The longest of the Berger 140s are a little longer at 1.412" for the Long-Range BT and 1.421" for the VLD, so give slightly lower Sg values, but still above the minimum recommended 1.4 unless you have very low MVs and/or shoot in very cold and dense air.
Berger recommends 8" for its 140s, but I think you'd be pretty safe at 8.5".

'Google' Millers Twist Rule and you'll find several sites where you can download the simple ExCel program. You do need to know the bullet length though. Anything over 1.0 is theoretically stable, but 1.4 or more is recommended to give a safety margin and allow for bad environmental conditions.

Laurie,
York, England

 

[GSSP]

Chad,

I''ve shot 140's VERY successfully in both the 260 Rem (1:9) and 6.5x47 Lapua (1:8.5). Buy the 1:8.5 and trust you'll be just fine.

Alan

 

[tunacan]

I have a Benchmark in a 1-8.5

I shoot the Berger 140s and have shot the Sierra 142s also with great success. I am in the process of trying to figure out my seating depth but here is a picture of a typical 6 shot group at 100 with the Bergers.

 

[chadjamesr]

Thanks for all the help. Accuracy One has some 8.5 twist barrels due to arrive next week and I'll be picking up one of them.