Too much twist?

[zoeper]

I am planning for a new build and need some advice on barrel twist rates.

Caliber: 6mm XC
barrel: 28" broughton SS
Bullets:75 - 105gr
I was thinking of getting a 1 in 8 twist barrel to stabilise the 105 VLD's and hope that the spin is not too much for the 75's and 88's

Can you overstabilize a bullet?

P

 

[406pat]

I'm not sure on what the numbers are for the 6mm but I would think having too much twist would limit velocity and perhaps damage lighter bullet jackets and decrease barrel life. Might also lead to higher pressures. In this application, I would think that the only problem would be limiting velocity. That's what I'd ask questions about if I was going to do it. Good luck!

 

[paste]

i have a 6mm Penrod with a krieger 1-8 twist barrel it shoots the 105 gr lapua scenars extremely well but when i shoot 87 gr v-max bullets they will keyhole at 500 yds. when i asked my rifle smith about it his reply was the lighter bullets have to much of a centrifugal spin that prevents them from achieving the proper arc when they are in flight and they penetrate the target with the tip of the bullet pointing upwards.
you might want to verify this with a second opinion

 

[zoeper]

Thank you Pat/ Paste,
You are right pat, i should make my mind up about the bullet first and then pick the tube (since it seems like you cant have one tube shoot them all)

The task at hand is to balance flat shooting with little wind drift and the best way seems to be hitting on the balistics calc.

What would be practical speeds obtainable from a 28 inch ss match grade barrel chambered for 6mm XC for each of the following?

75gr Hornady V-max
80gr berger
88 gr berger high bc FB
Berger 105gr VLD
115gr dtac

Pieter

 

[Locknload]

Pieter,
I am running a 240 Laser with a 28 inch 1-8 twist Krieger barrel.

The thing to worry about is not over stabilization, it is tearing the jacket off the bullet. If the bullet holds together there is no such thing as over stabalizing a bullet. I found out last weekend that the 6mm Sierra 80s and 100s just will not hold together at 3,700 fps in a 1-8 I am also told that the 107 Sierra will not hold together at the velocity of the Laser.

However, the 107 Berger VLD will stay with you all day long at 3,800.

Now to drop down in weight from the 107 Berger you need to switch to the Nosler BT bullet which I understand will stay in one piece down to 55s pushed at 4,300. Nosler brags that you can not tear their jackets off. I have talked to the previous owner of my 240 gun who says that he tried and tried to blow the Noslers up but they held together.

The 240 laser is a 280 with the shoulder moved forward .250 inches and changed to 45 degrees then necked down to 6mm. It is very similar to the old 240 Gibbs. It is a LR rifle built for rockchucks and ground squirrels.
Best,
Ed

 

[zoeper]

L+L,
I've heard of bullets going up into a puff of dust as soon as it leaves the barrel. I also know a guy who shoots the 6mm nosler bt 55grainers @4250 from a 1 in 8" twist barrel on a stock standard .243 Win without any problems.

I do however beleive that the extra twist puts a lot of strain on the bullet's forward acceleration that is probably a good thing for such a light bullet. It could even save you a grain or two of powder by holding it back while presure builds??

Fo myself i have decided on a 28" Broughton 5C 1/10" twist for the 80-90grain bullets. This should be a good compromise between fast/ flat while still retaining some BC to buck the wind and maintaining a little more energy for the slightly longer shots.

What is the life expectancy of your barrel while shooting the 107's at 3800??

Thank you for your input

 

[Mikecr]

Some math I use predicts V-Max failure at >3400fps in 8tw.
But QuickLoad implies to me that you will not reach this MV with safe pressures with a 6xc/28" barrel(I have one myself).

Whatever causing 'keyholes' at 500yds was not stability. Unstable bullets don't make it 50yds. Overstable bullets are pure myth, as all bullets go off scale gyroscopically stable down range, due to velocity dropping with very little spin loss.
So if the myth were truth, all bullets would keyhole down range.

 

[Locknload]

Zoepr,
I responded to your note but for some reason the response did not post. So we go again. The barrel would not last long at 3,800 fps with the 107s.

The 3,800 fps load is a max load and noted only for refrence in the discussion of 1-8 VS other twist rates. I do not run max loads for anything, unless it is the most accurate load for a cartridge, which is very, very rare. The accuracy load for the Laser is just above 3,500 fps with the 107 Bergers. I suspect that the accuracy load should give the barrel a life span of many thousands of rounds as the barrel is very slow to get hot, about 10 rounds at 70 degrees.

By the way, I run several cartridges in rifles with fast twist barrels and prefer heavy bullets in most of the rifles I shoot. I have found that the long bullet to bore diameter tends to only require X velocity to be a very effective long range bullet. In that regard I am running .224 guns with 1-7 twists, 6.5 guns with 1-7.5 and 1-8 twist barrels. It is a process of allowing the bullet design to do the heavy lifting.

Oh, I think it would be good and fair to add something here. The experiance with the 6mm Sierra bullets is very odd for me as I run the Sierra .224 bullets and the 6.5 bullets at high velocity in a fast twist without any problem at all. So it would appear that the 6mm Sierra bullets have a jacket or a jacket design that does not lend them to a fast twist at high velocity or at least a velocity of 3,700 fps in a 1-8 twist barrel.
Best,
Ed