mark II FV 10 round mags??

so this is probably a very stupid question but here it is. i just bought my gf a mark II FV 22lr that is the heavy barrel, it came with 5 round mag. my question is can i put my mark II F 22lr 10 round mag in there? i figure i can but why wouldnt they just sell them with 10 round mags to begin with?

second question does anyone make a high capacity mag for the mark II, if so where.

thank you
dylan

5 and 10 rounders are interchangeable.
Cost, many people don't like the way the ten round mags stick out, and other that that I don't know.
No.