14 twist barrel and 68 gr .224 bullets

[sewwhat89]

Can a 1:14 twist .22-250 stabilize a 68gr SMK or the like? My gun loves the 52 SMK/AMAX and 55 gr BT, but I would like to piddle with some bigger bullets. It shot some factory 60's ok, but I want to go to some better wind-bucking bullets. Is it feasible to try it or would I be wasting my time and money?

.22-250 Rem Varminter 26" tube

 

[Nomosendero]

I saw it tried in a .223 of 1:12 twist day before yesterday
& it did not work at all. I was shooting a Rock River Arms
.223 with 1:8 which for an autoloader is very accurate, .3-.4" 5 shot groups with bullets from 60-77 Gr. My friend tried 68's in his accurate bolt gun & it was a joke. Granted, the higher velocity of the 22-250 would help, but
his 223 is 1:12 & with your 22-250 being 1:14, I seriously
doubt it. I would try to borrow 5 rounds for a group if you
know someone that shoots them.

 

[bailey1474]

Lerch tried it in a factory Savage w/a 12 twist. Keyholed @ 100 yds.

 

[brianwinzor]

My experience is that a 1 in 10 twist is needed to stabilise the 68 and 69 grain bullets.

Just after the 68 Hornady and 69 Sierra became available in Oz in 1986, I built up a custom 220 Swift AI, with a 1 in 12 twist barrel (gunsmiths suggestion). However, quickly found that despite reaching about 3650 fps with these bullets, they keyholed into the target at 100 yards.

About 2 years later built up a .224 Clark with 1 in 10 twist, and the 69 grain Sierra grouped well at velocities of 3850 - 3900 fps. About 2 years ago, and after about 1600 shots, I had that barrel set back, and rechambered to the 22/250 AI, and when using the 69 grain Sierra, it consistently groups between .25 and .5 moa with a variety of powders at velocities of 3350 - 3430 fps.

About 35 years ago, I owned a custom 22/250 with a 1 in 14 twist barrel, and it liked and shot best with the Sierra 53 grain HP (3700+ fps). It gave reasonable accuracy (.75moa) with the Hornady 60 grain soft point, but it definitely seemed to prefer bullets in the 50 - 55 grain range. Brian.

 

[jkrische]

I remember seeing somewhere recently a "dumbed down" version of the equation to determine the twist required for a particular bullet. Unfortunately, in my old age I forgot what is was. Do you happen to know what it is?

 

[jkrische]

Thank the Shooting Gods. I found the equation in the Sept. issue of Shooting Times. It's known as the "Greenhill Formula". The equation is as follows: T x L = 150 where T is the twist rate in calibers and L is the length of bullet in calibers. This applies to lead bullets specifically but can also be used for jacketed lead bullets. So for a .224 caliber bullet; For a 1:7" twist the Max bullet length, L= 150/T (31.25 in this case for a .224 diameter; 7/.224). Max bullet length (est.)= 150/31.25 = 4.8 calibers.
4.8 x .224= 1.0752" Max (est) bullet length for a 1:7 twist. This is an estimated value but it should be fairly close. This length does not include any plastic tips.

 

[tbob]

well, this comes from shilen barrels, so it oughten to be good-- 1:14-55gr; 1:12-63gr;1:9-70gr; 1:8->70gr and vld.

a 1:14 in my experience is about 52gr max bullet for accuracy.

regards, tbob

 

[Mikecr]

Thats right TBob.
Greenhill shows 10tw for the 69 Sierra, >2800fps & bullet measuring .898" long. But thats marginal really. With more precise software I get a 10tw Sg of ~1.27 @3500fps ICAO conditions. At 2500'ASL, and 75deg, Sg goes up to 1.43.
So 1:10 should work. But 1:9 is perfect - Sg @ ICAO = 1.56
If high enough in elevation, and really smoking it, 1:11 technically might work. But forget any twist slower for that bullet.