.22-250AI twist rates

[Arizona_Mike]

I'm thinking about building a .22-250AI with 26 or 28" BBL for several roles from long-range varmint to long-range target, to possible smaller big game. AI not for any huge velocity improvement but for the excellent brass life improvement.

I'm not so worried about twist for hunting because you can get some pretty heavy hunting rounds with flat tails, so let's look at the target role being compatible with the varmint role.

I'm getting some pretty scary RPM calculations for some light varmint bullets at 1:8, so I'm taking a long hard look at the 1:9 which is generally not known to grenade lighter bullets mid-air. At the velocities I'm expecting they are working out pretty close to 1:7 5.56x45 RPMs (from a 20" barrel). I think if I stick to varmint bullets above 50gr I won't be overstabilized.

Looking at the altitudes of places I target shoot: 3 rural properties ranging from 36-74 acres and great backstops (4,200 ft to 5,000ft)--one at 6,400ft but I am rarely there and Rio Salado Sportsman's club (2,100ft). Excluding the most remote one, daily mean temperatures do not get below 38F in the depth of winter.

I was surprised to see that I can get a 1.5 stabilization factor for a 70gr VLD at 3500 fps and 2,100 ft elevation at any temp above 43F or a Berger 73gr Match BT @3450 fps down to 16F. Stepping it up to 4,200ft altitude, I could get a 1.5 stabilization factor for a 77gr OTM @ 3400 fps as long as it is warmer than 39F. Since the 77gr OTM only has a 1% better BC than the 70gr VLD, I don't think it would ever catch up to the faster VLD. At 4,200 ft I can shoot as low as 5F for the VLD. Above freezing I can go as low as 2700Ft which covers a lot of mileage around those locations.

Will I be able to get the versatility I'm looking for with a 1:9 twist?

Mike

 

[Archie]

Sounds reasonable

Mike, I think you've answered your own question. Your rifle as you anticipate will do all you seem to want.

I have a regular (Remington) .22-250 with a 1 in 12 twist. I can stabilize - barely - a 70 grain Sierra round nose, flat based bullet. However, it will NOT stabilize a 69 grain, HPBT with Spitzer shaped nose. The latter bullet is a bit longer. So your 1-9 twist should stabilize them both and be useful for long range shooting and hunting critters up to deer or pronged horn antelope. (I should think.)

If you shoot light bullets in it - 50 to 55 grain weight - they will spin pretty fast. But I don't think they'd be unstable; a fair amount of over spin is much preferable to a little bit of under spin. AND, you can load the lighter bullets a bit slower. Probably you will not use those light bullets on anything more than targets and varmints.

Bullets in the 35-45 grain weight designated for "Hornet" might be susceptable to either 'blowing up' from high revolution speed and surely destroying itself on contact with much anything. So I suggest you don't use those. At least not in 'normal' circumstances.

 

[WVRJ]

1 in 9 should be good up to a 75 gr bullet,and given the higher velocity of the 22-250(AI or not),it should turn enough rpm's to stabilize even the longish 75 gr VLD's.A 1 in 10 probably would go as far as the 69 gr offerings.Most twist rates for bullets in this class are computed at 223 velocities.Faster velocity,faster spin,more stabilization.I'd be interested in knowing how it works out for you.

 

[Arizona_Mike]

I was thinking that going in but that's not how the calculations worked out. Still the 70 great VIDEO shows a lot of promise.

Mike

 

[Arizona_Mike]

"Grain VLD", not "great video". I hate my phone some times!