ratchet rifling question

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madcowbreeder

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I am looking at getting a new 308 barrel put on my savage 10 and I see shillen offers ratchet rifling for the 308 but only in 1:13 twist, what would be the heaviest bullet you could shoot through that barrel..accurately?

And also do you get more velocity with the bullet on custom barrels as opposed to factory barrels
 
It's not weight so much as bullet length. I have successfully shot 180 grain hunting bullets from a 1-14" twist target rifle - they're pretty short bullets, with a flat base and a relatively short spitzer.

I know that a Sierra 190 won't work in a 1-13" Krieger.

A Sierra 175 will work in a 1-13".

What 180s are you interested in firing?

(I should go see if Berger 185s might work in a 1-13", hmmm....)
 
rnbra-shooter said:
It's not weight so much as bullet length. I have successfully shot 180 grain hunting bullets from a 1-14" twist target rifle - they're pretty short bullets, with a flat base and a relatively short spitzer.

I know that a Sierra 190 won't work in a 1-13" Krieger.

A Sierra 175 will work in a 1-13".

What 180s are you interested in firing?

(I should go see if Berger 185s might work in a 1-13", hmmm....)
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Yes, the lenght of the bullet is key, but speed is also important, the more FPS the more RPM and propability for the bullet to stabilise. If you can keep the speed of the bullet around 2700FPS or more out of 13" twist barrel in 308 cal the sir Greenhil formula says that the bullet will be stabilised up to and included 1,240" in lenght. 308 Win won't do that kind of speed with those bullets so I would stay with bullets no longer than 1,187" in lenght.
 
I regularly shot 178 grain Amax's from a 14 twist hart barrel on an old Enfield action. they stabilized just fine.

13 twists will stablize virtually anything you'd care to shoot from a 308 cartridge. I'd want a 12 so I could use the 200-210 grains for fun.

The bigger question is why the fascination with ratchet rifling?
 
oh i don't know why the fascination, i hear people talk about 5R rifling in and how much better they are with velocity and barrel life. And since I shoot a savage, a shillen barrel would probably be the only option I would have for that kind of rifling. At least that is just what I think, but please enlighten me with further ideas.
 
Obtunded said:
13 twists will stablize virtually anything you'd care to shoot from a 308 cartridge. I'd want a 12 so I could use the 200-210 grains for fun.
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Ian, you're saying I could switch from 155 Amax's to the Amax 208's without trouble in my 1:13 barrel? Because the BC on the 208 is so much better than that of the 155.
And if so, I have 650 Amax 155's I'll be willing to part with. :D

I wonder how much more recoil I'd notice.
 
To a first approximation, all that matters is bullet length and barrel twist - to a first approximation, velocity does not matter.

It is only to a second order approximation, that bullet velocity starts to matter (more specifically, that the bullet's drag coefficient slowly decreases with increasing velocity). Note that bullet RPM is not directly involved in determining stability, it's a twist-versus-drag relationship.

I have that sort of thing from the TR crowd before as well. I can never bring myself to trust buying a barrel for it though. So, if a long twist is better for a ~150 gr, and 175s work in a 14 twist, why do so many militaries use 10-11.25 twist?
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Why is it then that barrels actually chosen, and recommendations made by bullet and barrel makers are so conservative, compared to twist/bullet combinations that actually work?

It's because if you don't have a quick enough twist, the bullets won't stabilize, and this has absolutely *catastrophic* effects on accuracy. It doesn't open up groups a little bit - it produces 10 foot sized groups at 100.

On the other hand, having a twist rate quicker than necessary will typically have somewhere between little to no effect on accuracy.

JBM has a version of their calculator that includes the Miller stability formula. Give it a try, be sure to correctly enter your bullet's weight, length and caliber.

There's no way a 208 Amax will stabilize in a 14-twist barrel, it's just too long. If you could get them to stabilize (e.g. in a 12 or quicker), you will likely be able to get a bit of a performance (wind drift) edge over 155s. You will have to tolerate more recoil, you'll be throwing about 35% more bullet mass, at (say) 10-15% less velocity, so Mr. Newton says you're going to get thumped 20-25% harder. Not a make or break proposition, but definitely a step in the wrong direction!
 
I wish bullet makers would prescribe an optimal RPM for their bullets, not wist rates. The analogy i have used is the 300 RUM versus the 300 whisper. There is a 3000 fps difference in bullets speeds. The optimal twists are diamterically different.
 
Berger's VLD's are pretty long ... Berger says the 1:13 will stabilize their 30 cal 175grnr's. From what I've read, I would make two generalizations.
1) The impact of velocity on rotational stability is not enough for most of us to worry about.
2) It is not possible to "overstabilize" a bullet. Once they are stable, they are stable. With the appropriate rate of twist, stability problems are more likely related to imperfections in the bullet ie: out of round, uneven jacket thickness, etc
 
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