I have 3 S&W 4006 Magazines that are suppose to 11 round mags and will only hold 10 rounds. Does anyone know why this is? The 10 round are suppose to be pinned but I see nothing to unpin.

Some of the magazines are very stiff and to get the last round inserted requires a lot of effort. Are you sure you are pushing hard enough? If so, then have you disassembled to see if there is something internal that is limiting the follower movement?

Its quite possible those magazines came from Canada where the maximum allowable magazine capacity is 10 rounds. What color is the follower?

I have had all mags apart.(3) one new and two used. They all have blue followers and the all have 11 holes to show shells. I have tried with a UpLULA loader and by hand. The two used ones are suppose to be 11 rnd and the new one is suppose to be 10rnd.