6.5mm twist rate question

[BradY]

Chasing a bit of user experience if anyone is shooting 6.5mm cals.

Do the Berger 140 VLD and hybrid bullets stabilize in a 8.5 twist at sea level? Velocity will be around 2900fps mark. I know a straight 8 twist is recommended but my preferred maker only have 8.5 twist option available at the moment. If not I will have to look at another maker.

 

[Clod-NC]

Hi By 1983
I have no experience of the 6.5,I shoot 7mm,and the recommended or "normal"twist for this caliber(7MM)among famous makers seems to be 1/10 for up to150grs pills(probably even heavier too);my rifle has a 1/8.5 twist(CZ 550) and since I've started shooting with it I never noticed anything wrong with bullets around 140grs,I recently tested 150 grainers and they're right on,so I believe you don't have to fear anything.Hope you come out all right with the project.

 

[TerryPohl]

Dont know about the hybreads but the VLD's will. I live about 100 miles from the coast, and they shoot fine hers in a 8 1/2 twist.
Terry Pohl

 

[gotcha]

Hi 1983, Why not ask your BBL makers tech dept? Bullet stability within a given twist rate is based on Length not weight. If they are "up to snuff" technically they should be able to answer your question without hesitation. Then "get it in writing" ;D There are folks here that can steer you to online twist rate calculators. You'll need bullet length specs to plug into the formulas. I think the 8.5 twst will probably be sufficient. Caveat: Key word is "probably". Why take the chance?

 

[B Mize]

Berger 140 VLD LR Match, 140 Nosler CC and 139 Lapua's all shoot fine in 8.5

 

[BradY]

Ive just got onto JBM and putting truthful local figures in for atmospheric conditions, bullet weight, length etc and it comes up as 1.4 and stable. So Im going to go for the 1:8.5 and worst case I will have to use 130's

 

[gotcha]

Good Show ! With input from CSS & JBM you'll be shooting those 140's in no time. My 6.5 is an 8 twst. For the life of me I couldn't get my Jack Daniels impaired brain to remember JBM last night. Just couldn't pull it up. Good luck w/ the project.

 

[jr600yd]

I shoot both a 260 and a 6.5/06 with 1/8.5 barrels 30" NO problem

 

[BradY]

One thing I have noticed with JBM is if I put in 6.5mm as the bullet diameter, it comes up less stable than 0.264" With the hybrids after a bit more research its coming up as marginal stabilisation now- I think I have more accurate figures. Being at sea level not up in the mountains, there is a little alarm going off in the back of my head. I think the 8.5 will be ok but unsure. Have been speaking to Walt Berger, and he will let me know next week when he is back in the office. Seems like a very approachable man and commited to customer service if he is answering emails while not at work

 

[BradY]

I got a response from Walt who by the sounds of it was on holidays but he went back to the office just to answer my question. Fantastic customer service. He said the 140VLD would work with the 1:8.5 twist. But I have found a local barrel maker to do me a straight 8 just in case.

Thumbs up to Berger for their support to international customers.

 

[1shot]

BY1983,
For what it is worth, I was one of the original testers of this bullet last January. I started with an 8.5 twist, but wasn't seeing the accuracy that I knew this bbl. was capable of. So, I switched to an 8 twist and they immediately started shooting "lights out". I have photos of that bullet printing groups holding sub MOA from 100-1,000 yards. As a back up to this recommendation, consult the Miller formula. An 8.5 twist puts you at 1.44 or on the bottom edge of stability, while an 8 twist give you a stability factor of 1.64. (1.4 being a recommended minimum and 2.0 could mean a loss of accuracy). My advice is worth what you paid for it, but I'd shoot those bullets in an 8 twist if it were me.
I hope this helps,
Lloyd