I have used several cryo treated barrels and it has it's pro's and con's. I have always had it done on new high quality barrels, never on a used barrel. So I don't know first hand if it will help that much on a used barrel. If you beleive the adds, it will help cut groups by 50%.

From what I have been told by some in the barrel making industry, is it may help make a 1" rifle into a 3/4" rifle, but that's about it, and if it's a 1/2" rifle you may not tell any difference at all. Basically, if your rifle shoots good, cryo may not help it all that much, but if it only shoots fair then you may see a difference. One maker even told me, that the the barrel shoots, the greater the difference you will see after the cryo, but is kind of a waste of money to cryo a great shooting barrrel. I have not heard of cryo actual causing a barrel to decrease it's accuracy.

One thing that cryo does do is increase barrel life by 20-25%. It does this by hardening the barrel enough to resist normal wear and tear, and throat erosion.