Tricky twist rate question

[TheSwede]

Can anyone answere this?

Caliber: .30-06

Is there any difference in velocity between 1:10 twist and 1:12 twist.

I know 1:10 stabilize heavier bullets but does a 150 grain bullet go faster in a 1:12 than a 1:10.

Regards!

 

[Float Pilot]

There is more resistance in a tighter twist. So maybe,,, because the other differences in the bore finish , metallurgy and rifling thickness might make more of a difference than the change from 1 in 12 to 1in 10.

 

[TheSwede]

When you say tighter twist do you mean that 1:12 is tighter 1:10?

 

[USSR]

No, the 1:10 twist is tighter than the 1:12 twist. While theoretically, a bullet in the 1:12 twist should go faster, the difference is so minute that it is of no consequence.

Don

 

[MistWolf]

All else being equal, the tighter twist will give higher pressures and increased throat erosion, however slight

 

[Beak50]

While were on the subject of barrel twist rate My Colt H-Bar has a 1-9 twist but I have been told to get a 1-7 twist for it is there any particular reason for that suggestion?

 

[fatcat4620]

1/7 is what the military uses and will stabilize heavier bullets. You dont need to get anything and you gun should run fine if you dont shoot 75 grain bullets.

 

[Float Pilot]

I agree with fatcat. The 1 in 7 twist rate was required to shoot the very long M856 tracer bullets, (which look like an arrow). The regular M855 62 grain green tip stuff only needed a 1 in 9 twist rate.

The length of the bullet is actually what dictates how much twist rate is required. In the old days with lead core bullets, they only way to make a bullet of similar weight longer, was to make it a hollow point boat-tail..
But these days we have people making Earth Muffin Californian Approved lead free bullets. So to get a bullet of the same weight they must be very long.

 

[TheSwede]

Ok thank you very much!!!

 

[MistWolf]

...In the old days with lead core bullets, they only way to make a bullet of similar weight longer, was to make it a hollow point boat-tail...

This is not quite true. While hollow points and boat tails do lengthen a bullet, VLD (very low drag) bullets are long for their weight by changing the profile to one that's longer and pointier with a shorter length bearing surface. Some VLDs are hollow points, but some are also FMJ. I think some also use polymer tips. Some VLD bullets do not use a lead core and are made of solid copper or bronze and have been doing so for decades