I have just returned from a week of hunting and load testing with my new .220AI. The rifle has a 26" 1:14" Krieger HB.
A few myths regarding 1:14" barrels have been disproved at least in my barrel.
1) The barrel handled the following projectiles with aplomb using RL17 all tested with 45 grains & RWS 5431 primers.
55gr Nosler BT
55gr Sierra SP #1365
55gr Sierra Blitzking # 1455
2) A 1:14" will handle a 60 grain projectile , mine does , shot 2 Red Deer with the 60gr Nosler BT. BTW load was
43grs RL17.
3) My hunting buddy has a M55 Tikka 22/250 standard factory twist 1:14, shoots 63 gr Sierras all day long as well as 55's.
4) all bullets seated to facilitate magazine feed with plenty of jump, don't know how much , don't care they all shot .6-.5" groups.
5) the one bullet that had issues was the 53gr VMAX , loaded with a soft load of 40 grs RL17 to fire form cases bullet holes were SLIGHTLY oval , so ramped up the load to 45.2grs RL17 , problem solved , this load produced the tightest group for 5 shots of 0.473" from fully formed cases and I expect in the hands of a good BR shooter this load will do better or maybe tweak the seating depth but it is a hunting rifle so all loads are to magazine length.
I was so impressed with the 55 grain Blitzking #1455 I went and bought up all the local store had, 900 in total.Incidentally , I ran a 3 shot test over my Magnetospeed using the 55gr Blitzking , the first was a fire form load of 41grains RL17 velocities :
1) 3545
2) 3472
3) 3491 Average 3502.
Second test was 45 grains of RL17 in formed cases, velocities :
1) 3873
2) 3879
3) 3885 Average 3879.
No pressure signs and I reckon I can squeeze another 100 or so fps out of this.
Interesting that the factory standard twist rate for .222-22/250-220Swift is and has always been 1:14" Also interesting is that Nosler list the test barrel for their load data for the .220 Swift 1:14" for projectiles ranging from 34-62 grains. And for the standard 22/250 Nosler list a barrel of 1:14" for all their projectiles except the 60 grain BT, 60 Partition & Varmageddon where a 1:8" twist is used but switch back to a 1:14" for the 64 grain Bonded Solid Base.222 Rem test barrel 1:14" for ALL weight projectiles.
If one intends to shoot projectiles in the lighter range of 40-55 grains , a 12 or 14 twist will certainly handle them and don't be at all surprised if those twist rates will also digest heavier projectiles to 63 grains.
The guy that talked me into a .220AI shoots one as well , he also makes barrels and happened to have a .22 cal 1:16" barrel laying about. So he fitted it up and well b*gger me if it not only shoots 40 grain Noslers BT's at warp speed but handles 55's as well.
Stability Calculators based on pure Math are all very jolly but seldom do they factor in the exceptions to mathematical rules, of which there are many and provide ongoing fodder for interweb debates.
For years the accepted twist rate for .30 cal Palma barrels was 1:14 and there are many shooters still using that twist rate.Then 1:13" A calculator says that the old Sierra 2155 Tug Boat has a stability factor (Sg) of 1.05 from a 1:13 barrel, with an Sg of 1.4 the minimum. Based on this alone one would not choose the 2155 Sierra from a 1:13"barrel BUT I would like a bottle of Glenlivet for every possible shot & Prize Meet won with this combination.Again fashion changed now in Palma barrels the flavour of the month is 1:11 & 1:12" barrels. I currently run a Schneider 1:12 28" in my Palma/Fullbore Rifle and have shot with success the following bullets.
1) Sierra 155 2155 & 2156
2) Nosler 155 CC
3) Berger 155 / 155.5 & 155 Hybrids.
BTW every body knows one MUST have a minimum of 30 inches of barrel to get to 1000 yards with 155 grain projectiles, I guess my Schneider must be the exception to the mathematical rule.
Now a stability calculator says that a Sierra 155 2155 will be stable in everything from a 1:10" to a 1:14" BUT if the Sg exceeds 2.0 one MAY gain SOME accuracy by going to a slower twist. So at a twist rate of 1:10 the Sg factor is 2.98, 1:11" Sg 2.46, 1:12" Sg 2.07, 1:13" Sg 1.76, 1:14" Sg 1.52 ! So which twist rate is more accurate ?
I would humbly suggest that for cartridges such as the 22/250, 22/250 Ack, 220 Swift , 220 Ack that really shine shooting lighter bullets as they were intended a twist rate of 1:12-1:14" will suffice nicely. I one wishes to shoot heavy for calibre/cartridge projectiles, then a faster rate is required ......... but maybe not !
Mike.
