In the AP Style Manual it is correct to put down ".22-caliber" when writing about a 22 caliber rifle.
I contend that "22 caliber" is more accurate than ".22-caliber" because you are actually stating that the bullet is 22/100 of 1/100 diameter.
My daughter is an editor of a small Midwest newspaper, and the police chief stated that a ".22 caliber rifle" was stolen. I believe that this statement is more accurate than a ".22-caliber" rifle.
A little input here would be welcome. I have seen my case stated previously in some publication, and I note that Speer manual always list calibers in their manual as 44-40, 44, and so on. the only decimal points are for the actual diameters of their reloading bullets.
Thanks
Jack