.243 to .243 Improved

[Gman]

I have a Sako 75 Varmint SS chambered in .243 Win, with a 1 in 10" twist factory bbl. My question is, if I rechamber to .243 Improved, will the extra grains of powder make the gain in velocity enough to stabilize 105-108 gr. pills ?

 

[bkmilw]

have you tried with your current set up cuz most factory .243's are 10 twist and they shoot 100's fine, just push em faster with your current barrel.If its the VLD's your after your gonna need an 8 twist regardless of AI or not.

 

[BRhunter]

The standart 243 is perfect to push 105 or 108 grs bullets,you
just need a fast twist,1/8). John Whidden was the winner,2007
2008) at Camp Perry with this cartridge.

Michel

 

[Gman]

Thanks for the reply. I use the Berger 105 BT's in my 6BR,8" twist), and was hoping that they might work in the Sako 10" twist if I can push them faster. They aren't stabilizing in the factory bbl. with the .243 Win chamber.

 

[joesr]

First off the 1:10 twist barrel will not stabilize bullets that require a 1:8 twist.

Here is why:

The key is rotational velocity in stabilizing the bullet.

Rotational Velocity: w,rotations per second)
Velocity: v,feet per second)
Rotations: r,revolutions per foot)

It looks like this: w = v/r

Given that the bullet is fired at 2800 feet per second,v),which is slightly slow)

In a 1:8 twist barrel,r in inches per rotation) the rotation,r) is 8/12 = .6667 feet per rotation.

Therefore, the Rotational Velocity,w) = 2800 fps/.6667 feet per revolutions or 4200 revolutions per second.

In a 1:10 twist barrel we can calculate the required velocity to rotate the bullet at 4200 revolutions per second.

It looks like this: v = r X w

The velocity,v) = 4200 revolutions per second X 1 revolution per 10 inches or 4200 revolutions per second X 1 revolution per .8333 feet = 3500 fps.


Now this calculation is to simply achieve the same rotational velocity with a 1:10 twist barrel as a 1:8 twist barrel at 2800 fps. There are many more factors that need to be taken into consideration when shooting a bullet through the barrel. Not the least of which is can bullet withstand the increased velocity.

Furthermore, I don’t believe you can achieve 3500 fps from a 105 gr class bullet with a 243 improved cartridge.

I hope this helps.

Joe H

 

[Gman]

Thanks for the info joesr. I'll just keep the .243 Win chamber and shoot it. I guess that I'll try some 90 gr. Lapua Scenars and see how they work. Strangly enough, the BIB 95 gr. pills didn't group as good as Hornady 87 gr V-Maxes. After the original bbl is shot out, I'll re-barrel to a 1 in 8' twist.,not sure what 'hot rod' 6mm chamber I want yet)