Re: Swift Scirocco II
Not a lot of data out there on the Swift Scirocco II .224 75-grain bullet.
Just got back from the range, temperature -6 F, so I wanted to know if my CZ 527 Varmint .223 Rem with 24" heavy barrel of 9" twist would stabilize them in cold dense air. My altitude is about 3300 feet. About 10 MPH wind quartering into me.
Got a best group at 100 yards of .625" and a best group at 200 yards of 1.50". Worst group was 2.625" at 200 yards.
The 10th shot keyholed a bit and was about 8" high at 200 yards, but the two previous shots of the group, #8 and #9, had 1.5" separation at 200 yards.
My loads were 22.5 grains of IMR4895 and 22.7 grains of IMR4895 in military brass. 22.7 grains was more accurate, so I will start working up to max load and see what happpens. Max load in Hodgdon data is 23.8 grains of IMR4895.
The 9" twist is marginally stable, as 8" twist rate is recommended. With a long barrel and a hot load, 9" twist should be stable. So if you have a .22-250 or .220 Swift or .224 Clark with a 9" twist rate, you will probably be OK. Guys with .223 rifles have mixed results with the 9" twist rate, from what I have gathered. The bullet is not quite as long and has a longer bearing surface than a Hornady 75-grain A-Max, so it should stabilize a bit easier.
.224 is the only caliber I have tried in Scirocco. I am sticking with Accubond in .308 caliber due to price and availability and being a very similar bullet. In .224 cal, the Scirocco is the only bonded bullet of its type I know about.
Copper fouling is usually heavy by the 10th to 15th shot, from what I have gathered, so it is probably responsible in part for the keyholing of my 10th shot. At 22.7 grains, powder is slightly compressed, but should be able to get a bit more in even with military brass. Might be best to use commercial brass if going for max loads. Bullet is seated about .050' off the lands, and I have no trouble with clearance in a CZ 527 magazine. Would probably not work in my AR-15 mags as the COL came out around 2.245" if I remember correctly.
The 22.7 grain IMR4895 load is accurate enough as is for hunting mule deer, but I hope to eliminate the keyholing, or maybe it will never be a problem as I will be hunting at a higher elevation in warmer weather for antelope and deer. -6F is colder than I intend to be hunting except for predators in the winter, in which case I use Nolser or Hornady ballistic tip varmint bullets.
The jacket is pure copper on the Scirocco bullet, which causes the excessive copper fouling. Pure soft copper is also why it opens more readily than harder gilding metal used in most other bullets. I eliminated Barnes X bullets from my short list of possible bullets due to the need for high velocity for reliable expansion. I expect shots out to 200 yards on mule deer. Guys with .22-250 or similar magnum should consider the Barnes solid copper bullet, as it will hang together at highest velocities and needs higher velocity for reliable expansion relative to Scirocco and Partition. The Scirocco II will be pitted against the 60-grain Nosler Partition as my big game .224 bullet, and final decision will be based on how it puts down a mule deer. The Trophy Bonded Bear Claw is only available in 56-grain in .224 cal, and that seems a bit light to get enough energy at .223 Rem velocities for deer size game. The Speer 70-grain bullet is not bonded, so I would consider it inadequate on a large mule deer where I need deep penetration.
So, I would say that a 9" twist barrel is uncertain for the .224 Scirocco in some cases, but if you hunt at elevation above 3000 feet in warmer weather with a more potent rifle, you might be OK, because 9 out of 10 bullets being stable at -6F and around 2600 FPS velocity in a 9" twist .223 Rem means you have lots of situations where conditions are more favorable for stability. Plus, new .223 Rem rifles can now be easily had with the recommended 8" twist rate, especially in the AR-15 platform, and with the necessary 24" barrel for max velocity.
Probably best to stay away from this bullet if your barrel is under 20" long. I'll stick with the Partition in my 20" AR-15.