Twist question for 6BR

[jefats]

I've read some of the experts say you cannot overtwist a bullet. If this is true, why opt for any of the slower twist barrels. Seems like a no brainer but I have the feeling it's not quiet that simple.

Any thoughts/experience on this subject?

 

[gambleone]

I think I have read on this site that depending on the jacket
& speed you can burn a jacket in a fast twist barrel. I'm using
a 75gr vmax in a 6br with 1/8tw 32.5 gr varget & I'm ok but
if I were to go with a thinner jacket I'm afraid I'd burn
the jacket. Hope someone else chimes in...

 

[Phil]

gambleone,

You will find some extra velocity with a slower twist too.

I believe the jacket issue is the rpm`s you get with the lighter bullet and the faster twist.

I have 6 Dashers in 14 twist/12 twist/8 twist and 1.78 twist.

 

[SS427]

Optimum accuracy is acheived by spinning the bullet just fast enough to stabilize it. A good gunsmith will tell you to select the heaviest/longest bullet you plan to shoot and go with the slowest twist that will stabilize it. When I ordered my 6BR the gunsmith quizzed me pretty good about the distance I was going to be shooting (100-200 yds) and the bullet I was going to be using (65-70 gr match). Not knowing as much as I do now, I wanted an 8 twist and he suggested a 13.5. I took his advice and am glad I did. The rifle is very accurate and at times shoots as good as my 6PPC.

 

[Frankr]

I know there are a few shooters who agree with me..I have shot the 6BR in a 14 twist since i been shooting it.
my guess over 12 years,,,i have yet to try a fast twist..why..because i can shoot 65-68 gr bullets into a hole from 100-300 yrds..it makes me very happy..in the ground hog hunting fields i have shot out to 700yrds very happy.
it satifies me for all i do..700 yrds is quite a poke..i like the flat shooting high speed bullets..over a fast twist slow moveing bullet . but im building a dasher in a 8 twist to go with the heavy bullets..I think unless you are going to shoot 600-1000 yard competition go with the 14 twist you will have a good time..even though i have see the 8 twist shoot some very good groups at 100 yrds,,i perfer the slow twist with the fast moving light bullets..its just more fun ...I have hunted with a 22-250 and know others who swear by the 250..its amazing what a light fast moving bullet can do at long range..i have seen a 14 twist 6BR shoot sub 1/2 3 shot groups at 400yrds..what more do you need.

 

[6BRinNZ]

The faster the twist the greater the potential to expose core inconsistencies, so shoot the slowest twist that will stabilise the bullet.

1-8 twist is supposedly more versatile but you normally run into throating issues as you would typically throat for the long projectiles, which means you can't seat the smaller projectiles unless you want to try huge jumps. I didn't know any of this when I started so I got a 1-8 twist throated for 75 v-maxes for varminting. Later my needs changed and I wanted to shoot 1k. Luckily Berger have a 95 VLD with a short bearing surface so it works well with a 1-8 twist short throat

 

[gambleone]

gambleone,

You will find some extra velocity with a slower twist too.

I believe the jacket issue is the rpm`s you get with the lighter bullet and the faster twist.

I have 6 Dashers in 14 twist/12 twist/8 twist and 1.78 twist.

Phil, That's what I meant when I said "75gr vmax in a 1/8 tw." If I were to go with a thinner jacket it may not
be able to hold up like the thicker jacket would.
I do like the extra velocity I get in my 22-250 using 40gr vmax in a 1/14tw.

 

[spclark]

I've read some of the experts say you cannot overtwist a bullet.

There's a lot of 'experts' (on internet forums & elsewhere) whose advice perhaps is best taken with a grain of salt... or maybe Valium.

Bullets are designed for an optimum twist rate depending on weight and diameter. General rule is shorter / lighter bullets will do well in slower twists while longer/heavier need a faster rate to stabilize properly. As 6BRinNZ noted, faster-than-optimum twists will also tend to make any latent bullet balance imperfections more apparent, sometimes dramatically so depending on the distance of your target.

Up to a point you can shoot bullets in a range of twists but at the extremes they'll either fail to stabilize (too slow) or come apart (too fast). Too, in really fast twists (1:6 for example) with bullets at the heavy end of the range for their diameter (6mm in this example) pressures can get really peaky from being spun up to the fast twist so rapidly.

So called ratchet or "gain-twist" rifling is available to overcome this. A slow twist is used at the throat end with a (relatively) faster twist at the muzzle. A few contemporary barrel manufactures offer this option if you need to go that route.