22-250ai and 90 grain smk
- Thread starter ed k
- Start date
you do not need a 6.5" twist. that will just put more strain on the bullet jacket at the velocities you will be pushing them at. just so you know, i successfully shot the 90 vld bergers out of my 7" twist 18" barreled ar-15 at 2600 fps, with no keyholing at 350 yards. the groups were great!!!
Wow, that'll be interesting to be sure.
I agree with Cmillard though, 6.5 certainly isn't needed with what velocity you'll be getting. Stability is not only the sum of bullet weight versus twist rate; it's rpm for a given length to diameter ratio. RPM is made by increasing the twist rate or velocity (or both)- you'll have plenty of velocity! A good read: http://accurateshooter.wordpress.com/2008/06/03/calculating-bullet-rpm-spin-rates-and-stability/
For example: Cmillard's 7 twist with a 90 at 2600 gives 267,000 RPM, with a 7 twist if you increase to that velocity to say 3100 (a guess at what your .22-250AI would do) with the same bullet then your RPM will be 318,000!
An 8 twist with the same 3100 FPS velocity will yield 279,000 RPM, still faster than Cmillard's load that stabilized fine for him and he shot the Bergers and you say you want to shoot the SMK which is shorter and requires less spin than the Berger to stabilize.
I bet an 8 twist with that kind of velocity would work, would help keep your bullet from coming apart and keep pressure lower.
That's a lot of powder behind a small hole - keep us posted!
Wayne
I agree with Cmillard though, 6.5 certainly isn't needed with what velocity you'll be getting. Stability is not only the sum of bullet weight versus twist rate; it's rpm for a given length to diameter ratio. RPM is made by increasing the twist rate or velocity (or both)- you'll have plenty of velocity! A good read: http://accurateshooter.wordpress.com/2008/06/03/calculating-bullet-rpm-spin-rates-and-stability/
For example: Cmillard's 7 twist with a 90 at 2600 gives 267,000 RPM, with a 7 twist if you increase to that velocity to say 3100 (a guess at what your .22-250AI would do) with the same bullet then your RPM will be 318,000!
An 8 twist with the same 3100 FPS velocity will yield 279,000 RPM, still faster than Cmillard's load that stabilized fine for him and he shot the Bergers and you say you want to shoot the SMK which is shorter and requires less spin than the Berger to stabilize.
I bet an 8 twist with that kind of velocity would work, would help keep your bullet from coming apart and keep pressure lower.
That's a lot of powder behind a small hole - keep us posted!
Wayne
ed, i would recommend against the sierra matchking. not that it is a bad bullet--it's a good bullet. it is because the jacket is way too thin and that is why sierra recommends no more than about 2600 fps for velocity. berger makes 2 versions of the 90 grainers. a hunting version and a target version. the target version has a thicker jacket, therefore more velocity can be attained without premature jacket failure. and at the velocity you will be pushing them, you need that extra assurance. the hunting version has the thinner jacket like the sierra. like i said, the 90 berger vld target bullets worked great for me.
Quick question, would a .22 Dasher be able to reach the same velocity as the .22-250AI with a 90gr bullet? And would there be any appreciable difference in barrel life between the two rounds? Would the small primer of the Dasher be able to ignite the slow powder required for the 90gr bullet consistently?
I could stabilize the 80 Berger VLDs and 80 SMK in my PacNor 1:8 28" 22-250AI. The 90 Berger VLDs would not stabilize in my barrel at 800' altitude. I really liked the 80 Berger. Cut the wind really good compared the 69 SMK-223 combo I was shooting the same day at 300-500 yds. Sadly, I haven't put the barrel back on since the initial load development. Really want to grab a box of Laupa 22-250 brass and fireform those for the next trip out with that barrel. IMR4350 and similar speed powders worked well. Luck, Tim
I called sierra and berger today to get some info from both. Sierra told me like you said that the bullet is to fragile for these velocity. Berger stated either if their 90 grainers should be ok. They did recomend a 1 in 7 twist or slower. The man at berger told me he shoots the smk 90 at 2950 with no problems but has heard there can be issues. More studing to do but i am learning thanks to you guys and talking with the bullet people. thanks ed
remember to have your smith put in a fair amount of freebore for your rifle. make up a dummy round, with the 90 grainer seated to your desired length, and give that to your smith. also, what kind of powder will you be using? i would recommend some h4350, varget, or some imr 4007 ssc for that bullet--im sticking with single base powders. also, wolf primers are my favorite.
Don't just limit yourself to the one (90gr. SMK) bullet, make up some different dummies in 80gr. as well (AMAXES are short) so SMK's and Bergers are the go to. My 700 .223 Rem. is throated for 90gr Bergers, with 90gr. SMK's, 80gr Bergers, SMK's and 77gr. SMK's all falling within the ogive window. Granted the 77's have to jump a little, but they don't seem to mind.
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