I received the 4 I ordered for my SP-01 Shadow. Steel base - as Smokeeater stated, tougher to load than original mags but all have worked through 250 rounds I pushed through today. One mag was a little harder than the other to load to 10. I'll take it apart tonight and see what is hanging up. I'm assuming the follower is getting caught up in the blocker. Otherwise great mags. Thanks Grumpy!