Picked up a Beretta 92FS in California with the darn full sized low capacity 10-round magazines. Found that I barely have the thumb strength using both thumbs to press the last two rounds in.

Like 60-70 pounds of pressure!

I've got some normal capacity magazines to try out but these California compliant ones suck! I'm no lightweight in the thumb department and have no problems with any other pistol or rifle in my collection. Just a warning to those who might think of buying one of these - start working your thumbs now.

The Glock 22 10 rounder is the same. I guess they really dont want you to get 11 in it...let alone 10. (the only mutant mag I own)

I wonder if all the Beretta 10 rd mags are like that? I am going to get one in 90 days, so I guess that will give me enough time to build up my thumb muscles! Enjoy your new weapon.

This problem is common to nearly ALL Klinton-reduced 10-rounders.  BATF regs essentially require heavy springs to deal with the over-compression required.  You see, if BATF thinks that there's any way for a design to be modified to hold 11 rounds, they won't approve it.

When my AR10 was new, I managed to get 10 rounds into the mags, but the bolt didn't have enough force to strip them off the mag.  The 20-rounders, which are properly designed, don't have this problem.  The solution was to work the springs with a ruler until they'd loosened up a bit.  That's much harder to do with a single-feed mag, though.  They'll loosen with use, but take some good advice:

[b]Buy an HKS loader[/b], which is the best tool for the job.

-Troy