Hi
Are 5 and 10 round magazines for an AR-15 the same length? Is the same true of the AK-47 magazines?
I'm asking this because I read that it’s a good idea to buy a 5 round magazine for an AR-15 or AK-47, because someday you might be shooting and defending yourself in the prone position, where a large magazine might get in the way.

If they both are the same length (and if there are no legal restrictions), why not just get a 10 round magazine?

Thanks in advance and have a Merry Christmas.

John