Thanks guys! Now I got it figured out. It's easy to see the difference once you lay one beside the other. Few other things that I notice. The 77/22 mag will sit flat on a level surface whereas the 10/22 mag will wobble. Also, the 77/22 mag has a "tab" on the rear of the mag to, I suppose, facilitate extraction. The 10/22 has no tab. One other thing, the 10/22 mags are marked "10 shot" on the front. The 77/22 mags are unmarked on the front end.