The only modifications I had to perform were to my Star plastic lowcaps. On those I only had to slightly file down the tab that goes into the latch. Otherwise I have some metal G&P midcaps, of which only half fit. It turns out that some of my mags got slightly deformed through rolling around on them, so liberal application of a hammer was required. Which makes my beat up mags look even better.

Basically I found that the tolerances on the Real Sword mag well and latch are very slim. Even the tab on the stock mag is tight when latched.