260/6.5-308 AI

[Jim’s Hunt]

8 twist
7.5 twist
7 twist

opinion poll here. 260AI 25-26" tube light to medium Palma contour shooting 140-147gr ELDM lapua 308 brass (not Palma) which twist will give the most FPS at 6300' elevation.This should be interesting

 

[Jim’s Hunt]

8 twist
7.5 twist
7 twist

opinion poll here. 260AI 25-26" tube light to medium Palma contour shooting 140-147gr ELDM lapua 308 brass (not Palma) which twist will give the most FPS at 6300' elevation.This should be interesting

Mistake on the 3. Should not be there

 

[jebel]

I don't think you'll find an appreciable difference in muzzle velocity between twist rates from 7 to 8. And muzzle velocity isn't affected by elevation, though downrange velocity is (irrespective of twist). If the 140 or 147 ELDM is your chosen bullet, then 8 twist will stabilize it just fine. If you wanted to shoot a longer bullet, you might need faster. For example, to shoot the 137gr Hammer Hunter, you'd need a 7 twist.

 

[lancetkenyon]

I am building a .260AI (6.5-.308 Imp 40°) also. Just waiting on my custom reamer with .140"FB vs standard .050"FB. I will be running the 140 Hyb in mine, with the option of a 129 AH, so I went 1:7.5". If you stick with a 140, the 1:8" is great. The 147 might benefit from a 1:7.5". Anything heavier would too, or a 131 HH/129AH. But the long solids like the 137 HH would need a 1:7". The 140 should still shoot fine from a 1:7" too.

 

[Hunt_4life]

Go with 8 twist. At least in 6.5 prc my buddy can't get his 7.5 twist to shoot with 140s.

 

[TRG65]

I run a 6.5 Addiction, 6.5x55 AI, instead of 260 but very similar. I have run 3, 8 twist barrels with 140 and 147s. However, I will go to a 7 to shoot the 156s for my next barrel. I will then run 130 or 123 for short range prs matches.

 

[Roughrice]

8 twist for 140-147 eldm.
My buddy shoots Berger 156 in 6.5 PRC with 8 twist.
I certainly wouldn't go faster than 7.5 twist in 6.5 in that weight class vs case size.

 

[del2les]

My 260 AI wears a 28" with 8" twist and shoots the 140-147's extremely well. I easily reach and exceed 3,000fps with the 140's.

 

[Coyote Shadow Tracker]

I shoot several 260s with 1:8 twist and shoot 123-SMK, 130-TMK, 142-SMK all the same POI @100 and 0.25" groups. Also shoots 150 SMK Great. I am building a 6.5X284 with a 1:8 for F Class with 142 SMK.. All the "F" class shooters with 6.5s I know use 1:8. If you go with a 1:7 of 1:7.5 they may be good for 150 gr and above, but you may have issues with the lighter bullets. If you want to shoot 123gr to 150 go with the 1:8. I don't shoot solids or HH so that may be a different story with twist rate.