I would think the .338 would be a good choice for this technology, as you could use 6.5s, 7mm bullets, each of which can have a high BC and SD on their own. Accellerated to 3,400+ fps they would be wicked.
Hum, I wonder how accurate those numbers were/are. As you can get .220 swifts (and others) to shoot a .22 at 4200 fps. I wonder if that sabot .50 was just a gimic? I'm hoping to get around 4000 with a sabot .22 in .308
Read my topic about Experimental Cartridge, part 1. We will try to make a sabot round out of it too, not only necked-down. The problem is getting hold of good sabots that have low friction, assemble with a superb fit, and separate cleanly from the bullet as it leaves the muzzle.
1209m/s for a .22 in a .308 casing? Hmmm, I think you should be able to get it somewhat higher... The 4.81mm 3.4g projectile in the Winchester SLAP reaches 1340m/s(around 4396f/s) and our current gen sniper round at 4.81mm and 6.2g reaches 1260m/s(around 4133f/s)
the cartrige your referring to is the 50cal SLAP round that has a MV of 3985 fps. the bullet used under the sabot is a 30cal AP bullet.
The 30 cal Lazzeroni Warbird is a wildcat Cartrige made by lazzeroni. it gets Very impressive ballistics on its own i.e. 3500fps out of the barrel and arrives at 500yrds with 2700 fps (i might be a little off). anyway just imagine what would happen if u put a 22 sabot in there!
At these velocities though it should be noted that the .22 bullet is under a lot of stress and is therefore very unstable in flight. Accuracy will suffer considerably. Also, with the exception of well constructed full metal jackets, a bullet at these speeds will vaporize upon leaving the barrel. However this would not be a problem with velocities in the 4000 fps range, as evidenced by the .220 Swift and .22-250 Rem that do it routinely.
Also, I wonder what would happen if you forego the sabot and take a standard .30 caliber bullet and drilled out part of it to lighten it down to about the grain weight of th .22 sabots you were planning to experiment with. What would the differences in velocity be? It seem that these would be more efficient at killing someone, due to the increased diameter and accompanying foot-pounds of energy.
Although I do suppose that the armor-piercing potential would be lowered with the larger diameter and surface area. Also, the rate of twist would most definitely have to be change down to about 1/9 or 1/8.5 to adjust for the greatly increased velocities achieved.