It depends on whether you have and old Wingmaster or a new one. The first one you have listed has the ratchet system to secure the magazine end cap. If you have an older Wingmaster and will remove the magazine cap you'll see a small ball that ratchets into a set of small notchces. If you have a newer gun, they changed the cap retention system and it won't have the ball and notches, so you'd have to order the second one you have listed.
Truthfully, either will work, but if you want to be picky and match exactly what is on your gun now, that's the differences. The detent system just makes sure the cap won't ever come loose.