I've had good luck with the RCBS 22 cal flat-point bullet that's supposed to be a 55, but ends up 60 when gas-checked, and cast of some variant of ww alloy and quenched. I've also got the NOE version of this mould in a 4-cavity that ends up about 59 grains out of the same alloys and gas checked.
Both of these have worked exceptionally well out of several 223's twisted 1:8-1:12, a 221 FB, 22 Hornet Improved, and a 218 Bee all in Contenders with 1:14 twist, and out of a 1-14 22-250. It is easier to get accuracy out of the smaller cases than it is with the 22-250, but in fairness, all the smaller cases are housed in custom aftermarket barrels.
I use Lee tumble lube, and have gotten them up to 2500 fps with decent accuracy, but the 1:8 twist seems to top out at about 2300. The 1:12 in 223 is a target gun, and will shoot the lights out using 16gr of either 110 or 4198. In the smaller cases, Longshot and Lil Gun have done well. In the 223, H110 and IMR4198 have produced the best velocities with best accuracy. The 22-250 ended up preferring IMR3031, and much over 2000fps, it wouldn't hold groups. Never did figure out why. None of these will shoot over 1.5" for 5 at 100. Often I can put several through the same hole at 50. Maybe a different alloy would allow for higher speeds. I'm quite happy with these results.
