Any one publish a G7 BC for Sierra's newer pointed .224 90gr SMK?

[skiutah02]

Have you had the vlds come apart in flight or did I read that wrong?

I wrote up this experience for Greg to ponder. Perhaps its worth sharing more widely.

http://faculty.cord.edu/rutherf/12/90vldblowingup.pdf

Drew

 

[BP1]

Good to know Drew thanks. I usually try to make it to the range a few days before our match and shoot 15-20 rounds then the 69 rounds for the match. I have a 100 on it since last cleaning.I guess you have planted the thought in my mind I need to get it out of the safe and clean it.

 

[ASbobcat]

I wrote up this experience for Greg to ponder. Perhaps its worth sharing more widely.

http://faculty.cord.edu/rutherf/12/90vldblowingup.pdf

Drew

Very interesting article. Thank you.

I just bought a used Brux cut rifled barrel to explore the 22BR. It's 8 twist and straight lands. I'm pushing 90grSMK's hard (3150fps) and was concerned about jacket damage if I let the carbon build up.
My real concern is that if I were to spend the money for a new 7 twist barrel to shoot the Berger 90's at that velocity, I could be putting a lot of stress on the jackets.
I'm hoping to avoid the issue with polygon rifling.

 

[ASbobcat]

There is another factor when comparing the SMK and VLD.

I am shooting a 22BR and found a usable max MV of 3150fps in a 28in bbl with RL17.
At these velocities a 8 twist barrel will stabilize the SMK (mine does), but probably not the VLD (not tried).
I just got a box of the new pointed SMK's which Sierra tech said were 1.171 long. The average length of mine are 1.158 with a range of 1.152-1.164 in a box of 500.
The ability to use 8 twist is important at these velocities because the centrifugal forces on the jacket in 6.5-7 twist would be significantly higher. Even if the jacket held together, there could possibly be some deformation depending on type of rifling.

 

[raptor1ronin]

Yes

Have you had the vlds come apart in flight or did I read that wrong?

I have, and so has another fellow in our club. He has had 35 so far. He's using a 6.5 twist.

 

[ASbobcat]

There is another factor when comparing the SMK and VLD.

I am shooting a 22BR and found a usable max MV of 3150fps in a 28in bbl with RL17.
At these velocities a 8 twist barrel will stabilize the SMK (mine does), but probably not the VLD (not tried).
I just got a box of the new pointed SMK's which Sierra tech said were 1.171 long. The average length of mine are 1.158 with a range of 1.152-1.164 in a box of 500.
The ability to use 8 twist is important at these velocities because the centrifugal forces on the jacket in 6.5-7 twist would be significantly higher. Even if the jacket held together, there could possibly be some deformation depending on type of rifling.

As a follow-up to my concerns about jacket integrity, I ran some RPM numbers for comparison.
My 6BR load of 2950fps with a 105gr VLD in 8 twist spins at about 265K RPM.
A 22BR with the same drift at 1000yds, 3150fps with a 90gr VLD in 7 twist would spin at about 324K RPM. And using Bergers recommended twist rate of 6.5 would spin it at 349K.
That's a LOT of stress on the jacket.

This revelation has caused me to abandon my 1000yd 22BR project and return to my tried and true 6BR. However, 3150fps using 90gr SMK in 8 twist would spin at only 283K and still be competitive up to 600yds.