I bought a John Masen brand 9 round magazine, which is supposed to be a copy of the Colt 9 round post-ban magazine, the nice one with the black plastic wedge floorplate and dark grey finish.  

The Masen mag looks good, but it will NOT easily insert or drop free from my Olympic Arms rifle.  It requires so much force that the magzine finish is rubbing off, clearly indicating the parts that are too wide.

I talked to the Masen lady on the phone, she was very nice.  "We know," she said, "Olympic makes their mag wells a bit on the tight side, that is the only rifle we have heard complaints about.  They sent us a lower receiver, we are going to change the magazine dimensions in the next few months to work in Olympic rifles".

In the meantime, I will return the Masen, and get me a Bushmaster 10 rounder.