I have a ca94 40 and you can get 30 round mags all over but thats all. If you needed a lower capacity mag you need to make a 30 rounder into say a 10 rounder by using rivets or such but the actual length of the mag stays the same. The bolt hold open is awesome! 40 hits harder on the target and the wallet. It comes down to you. You already have an SW5 might as well try the 40 right???