Ideal twist for 95 grain Sierra match bullets?

[SS427]

I'm wanting to build another 6mmBR rifle for 300 yards at the range and out to 500 yards varmint hunting. I am intending to shoot 95 grain Sierra match bullets and lighter varmint bullets. Would a 1:10 twist barrel provide stability for the 95 grain Sierra's?

 

[RonAKA]

If you can get the necessary dimensions you can calculate stability with the link below. Be sure to enter your 10 twist to see what stability it will give you.

http://www.border-barrels.com/barrel_twist.htm

Berger says 9 is minimum for their 95 grain VLD, so the SMK will not be a given to work. If shorter than the VLD there may be a hope that it will.

 

[mbkmkk]

The box for the 95 grain Sierra's states 9 or faster.

 

[SS427]

Ron, I never trust what a programmer tells me. I'd rather rely on the advice of those who have actually shot the bullets in a 10 twist. I know the Berger 95 VLDs need a 9 twist or faster, but the BIB website says this about their 95 grain bullets:

6mm- 95 Gr. FB, BC-.45 : Made in Niemi carbide dies; 11 ogive/.052″ meplat; .2435 pressure-ring; .2433″ shank. Ideal twist: 1:10″ twist; works well in twist rates as fast as 1:8″

I'm assuming the flat base is what makes the difference.

If the Sierra box says 9 or faster, I will either have to pick a different intended bullet or go with an 8 twist barrel.

 

[RonAKA]

Ron, I never trust what a programmer tells me. I'd rather rely on the advice of those who have actually shot the bullets in a 10 twist. I know the Berger 95 VLDs need a 9 twist or faster, but the BIB website says this about their 95 grain bullets:

6mm- 95 Gr. FB, BC-.45 : Made in Niemi carbide dies; 11 ogive/.052″ meplat; .2435 pressure-ring; .2433″ shank. Ideal twist: 1:10″ twist; works well in twist rates as fast as 1:8″

I'm assuming the flat base is what makes the difference.

If the Sierra box says 9 or faster, I will either have to pick a different intended bullet or go with an 8 twist barrel.

I'm the opposite. If I know how the stability is being calculated and it makes sense with some actual results, I tend to trust the computer more than internet hearsay, unless it comes from a very trusted source. The Border Barrel site uses the McGyro code which is quite sophisticated. The Don Miller formula is a good start, but does not compensate for bullet shape or density. The McGyro code considers both. Also I've had two bullets go unstable and after the fact I calculated stability of them with the McGyro code to be about 0.98 and 1.02. At higher temperatures they were OK, so I think the code is close.

For sure flat base vs boat tail is a big factor. And VLD vs standard boat tail is a big factor too. I'd guess a standard boat tail at 95 grains would be fine except for low altitudes and low temperatures. So as I say the Sierra may be fine. I would get some measured and see what they come out at, or just shoot them.

I ran the Berger 95 VLD through the code at standard temperatures and altitudes, and it came out just over 1.1 for stability at 3000 muzzle. That may be good enough, and you may get away with them too. At 80F it goes up to 1.15. And I suspect the Sierra is shorter than the VLD, so it should be better still. See graphs at link below for the VLD. If you shoot in cold temps then the VLD's are likely to shotgun based on my experience.

Berger 6mm 95 VLD Stability

 

[SS427]

I should have clarified that I only rely on select advice, cause there is a lot of opinions out there based on speculation and no actual experience. I was hoping a few of the more trusted names would speak up, but could be they are not using any ten twist barrels as most the guys run eight twist or a twelve twist.

I've worked in the computer field long enough that I don't trust computers in general and I know the output of a program is only as good as the programmer and the input. My Turbo Tax program this year tried to screw me out of $150 bucks! Good thing I double check stuff like that the manual way. I don't have any of the bullets to measure, so it would be garbage in/garbage out if I used one of the programs anyway.

The Sierra 95 match bullets have a very deep boat tail, so they may very well require a 1:9 twist like the Bergers.

 

[AckleymanII]

Otter, You should not expect those bullets to expand on varmints.

 

[vlcakc]

My 6X47 Lapua 1:10 PacNor shoots the 95 gr Sierra MK very well. However, if I were rebarreling specifically for that bullet I would use a faster twist just to be sure. Vic

 

[RonAKA]

The Sierra 95 match bullets have a very deep boat tail, so they may very well require a 1:9 twist like the Bergers.

I found this link which gives the length of the 95 SMK as 1.182. That is longer than the 95 grain VLD which is 1.150, and almost as much as the Berger 105 HPBT, which Berger says needs a 1 in 8. So, yes you would be really pushing it to use a 10 on the SMK. That is one long bullet for the weight. It must have a nice BC for that weight though.

Sierra 95 gr. SMK

 

[SS427]

Thanks Ron. As always good advice from you.

I followed your link, and by clicking on another link found this from a 2007 post on the 6mmBR website:

EXCLUSIVE AccurateShooter.com Report
Sierra Bullets has a new 95gr, 6mm boat-tail MatchKing bullet. It is optimized for 1:10 (or faster) twist rate barrels.

I think a 10 may or may not work....probably would depend on the gun and the conditions.

Keith - I didn't write my orginal post clearly. The 95s are for targets and I would use 87 grain V-max and/or 80 grain Nosler ballistic tips for varmints.

 

[RonAKA]

I think about the only way they could be keeping a bullet that long stable is by having a very large hollow cavity in the nose. It would be interesting to see a bullet sliced in half lengthwise.