to change my hw45 177 to 22, is it just a matter of changing the barrel itself?

where's the cheapest place to buy one mail order? are there any restrictions on buying these mail order?

any one know why the .22 version never used to have 2 stage cocking? i know the new ones have. i'd've thought that it'd be much simpler to manufacture a single model with different barrels than make 1 & 2 stage models.

thanks.