Bullet Velocities

[D.Hayden]

Is there any general rules of thumb for the combination of

1) Barrel Twist

2) Bullet Weight

3) FPS

Like.. (generally) :

55s in a '1 in 9', best accuracy is around 3,000fps..

69s in a '1 in 8', best accuracy is around 2,825fps..

75s in a '1 in 8', best accuracy is around 2,700fps..

something along those lines?

Or is this too barrel and powder dependent?

And, for rifle, when people are working up a load, how much is your increment/delta to the next charge? .2 grains, .5 grains, etc?

Thanks..

[Dan Sierpina]

Quite often load density has a lot to do with the accuracy. A load with a lot of airspace usually doesn't shoot as well as one that's pretty full. That of course is using powders in the right burn rate.

The numbers you listed, bullet weigh and velocity seems to be in the range of higher end velocity for the bullet weight. You can only get so much speed out of a given case capacity, without making a mess of things. If you need more speed, you need more capacity.

The twist rates are simply needed to stabilize the bullets. Length is the factor, not simply weight. Someone was making tungsten core bullets in .224 and .308. Very heavy but short for the weight. I think an 87 grain .224 would stabilize in a 9 inch twist. Rather than a 7 or 6.5 inch twist.

The serious highpower shooters will give up a little speed for best accuracy. Of course if the most accurate load with a certain powder is several hundred feet slower than what the cartridge is capable, they'll try other combinations to get the speed up too.

I hope this is the type of answer you were looking for.

You can check ot 6mmbr.com for more info.

http://www.6mmbr.com/223Rem.html

Edited September 5, 2007 by Dan Sierpina

[Keith_J]

It is bullet length, not weight, that dictates twist rate. And also construction to a lesser extent. Search "Greenhill Formula" for greater depth on this subject.

[MasterLefty]

Some of the formulas can be found here here.

Kenny

Edited November 6, 2007 by MasterLefty