Uncle Jack . . Your question about those calibers is - basically they are alive in a different name. 5.6x57 is now the .22-244 (6mm) 2.241 inches, and the 5.6x61 is the .22x06. Basically . . the 06 is a little different but the dim. 61mm comes out 2.401 by my calculations, ("X"mm x .03937 = inches) 5.6 = .2204". There are two distinct .22's in the upper range right now the .22-308 (243) and the .22-244 (6mm Rem) that are kind of dominating the .22 shooting, there are a lot more, these two just seem to be at the top of the mix. Then there is the .22-244 Ackley Improved which I am inquiring about, and I was plesently supprised at how many of them are out there. Some people have been experimenting with them for years, I am just reciently getting into this kind of shooting, and what an interesting field of fire it is. Most people - except those that are really into the long range shooting, don't shoot much over a box of ammo a year and then if it will hit a 10" plate at 100 yards think - boy that really shoots good. But these calibers will shoot into that 10" plate at nearly 1000 yards, and it is a very large target at 500+, and a coke can at 1/4 mile is just a "good target". I'm trying to get this one inside of minute of Coyote at 600 yards with a bullet that will get there . . . ;D ;D