Over-stabilizing a bullet?

[LRSickle]

I just finished a new build. It's a 6mm Ackley Improved with a 1-8 twist. I originaly wanted to shoot 105s and 107s but the throat is a little short so, thinking that the longer bullets would eat up some case capacity, I tried some 75 Vmax and 75 Sierra HPs. The Sierras flew incredibly well. A guy that has a similar set-up was surprised that I could get a lighter bullet like a 75 to fly so well out of such a tight twist. I know a tighter twist robs a little speed but can you over-stabilize a lighter bullet to where it ruins accuracy??

 

[BigSkyGP]

I think it will depend a lot on the light bullets construction. Light jacketed varmint bullets may come apart after leaving the barrel from too high of an RPM, due to the tight twist.

How ever I think if the bullets hold together long enough to hit say a P-dog, could be quite spectacular!

I don't think it will hurt accuracy enough to worry about.

 

[Buffalobob]

The 95 Berger has a very short bearing surface and a high BC and likes a fast twist.

Jam it to test loads and then ease it back a little.

 

[blipelt]

I have a unique chance to talk with Richard Schatz quite a little. When visiting with him about fast twist light bullets he mentioned some of his friends were doing it. They turned a pdog into red mist. "They hit like Thor's hammer" he said.

Brent

 

[rscott5028]

Let's just theorize that you might do a little better with your rifle and 75gr bullets if you had a little slower twist.

But, it obviously hasn't completely ruined your groups.

 

[Boss Hoss]

Even if the bullet flies true------if spinning TOO fast will upset excessively at impact causing the bullet to fail. Lead core but the copper I do not know about.

 

[squirrelduster]

My Hart barreled 8 twist 6br was set up for long range squirrel shooting with the 105 and 107's but it shoots the 75 vmax really well and is a grenade when it hits. Seems that ricochets are minimal too.

 

[LRSickle]

Maybe my friend's gun with a 1-8.5 twist just didn't like the 75s. I just couldn't imagine him not being able to get the same groups as he can with the 105s he's shooting right now.

 

[Forester]

I think excess twist has more to do with accentuating any flaw/imbalance in the bullet.

My 8 twist 6BR shoots like a house afire with 80gr Bergers. So well in fact that I have yet to get around to trying the 105s, though I will be soon. I know it does not like 95gr VLDs well at all though.

 

[LRSickle]

I think excess twist has more to do with accentuating any flaw/imbalance in the bullet.

You might have hit it. A couple days ago I was shooting .14 - .25 groups with some pretty mild loads. As I increased my charges I started to get random fliers. I was trying to find my max velocity. When I backed my charges back down my groups came back together. Maybe my friend is just driving them way too hard.

 

[royinidaho]

LR,

I think you're onto the problem. I wonder if an 8 twist is as necessary as advertised.

I've found that Hornady Interlocks and Nosler Accubonds/Ballistic Tips to be the hardiest jackets. However, in 6 mm they have lousy BCs......

I've pushed Hornady 140s, Nosler 130s, 140s, 150s to unspeakable velocities out of an 8 twist - 3 groove barrel in 277 without any problems.

I have duplicated your findings with several other factory and custom bullets.

 

[MontanaRifleman]

I'm not an expert on your particular chamber, twist and bullet... but in a conversation with a custom bullet maker with a lot of experience, the issue with "over stabilization" is, at long range your bullet's nose remains oriented "up" and doesn't follow the arc of the bullet path. This is only a concern where deep, reliable and predictable penetration of let's say a large game animal is concerned. In an over stabilization, at long range, the bullet will likely start to tumble on impact.

As far as accuracy goes, that's anyone's guess, and I really don't think the difference in twist in a 6mm AI is going to matter when penetrating paper or varmints. If you're over speeding a thin jacketed bullet, that's another story.

 

[montana_native]

Physics of bullet flight aside, I had the same concern as you but empirical data out of my own gun suggests there is no concern. I've got the 6mm AI with an 8 twist. It shoots the 75 v-max at 3750 with no issues and groups about an inch at 300 yds. Gophers still explode out to 700 yards or so. I've yet to make a hit beyond that distance. Don't be afraid to seat the 105's deep. I'm seating to magazine length (2.820") and getting 3275 fps with Retumbo and very good accuracy.

 

[TAC]

Why not pick up a reamer and set it up the way you want? Your smith should be able to run it down your current barrel chamber and extend the throat. PT&G also sells throat reamers

You'll always have the reamer and can chamber your next barrel to the same dimensions - it's a good way to go.


TAC