FX Royale .22 mags

I recently bought a used FX Royale .22. It came with 2 mags, one 12 shot, and the other 11 shot. 

The 12 shot works perfect, but the 11 shot won't seat into the breech all the way. 

Upon inspection it was obvious as to why. The "channel" on the smaller mag wasn't long enough to slide all the way in.

I have contacted the seller and I'm sure he'll replace it, but I know he has many many guns and I'm wondering what that mag actually fits. It's definitely an FX, but other than that I don't know.