I've done that above, you have to be a bit careful with these magwell converters and what M4 mags you use. I bought a SocomGear one that broke when there was a bit too much wobble because my KA mags didn't fit all that well so the feed "lip" snapped. Found the now rare PrivateParts converter, much much more solid but it didn't fit half my mags. Finally bought 1 from UNCompany made by Classic Army, fits nice with no wobble, feels solid, no feeding issues to report any of my mags. The only one that doesn't fit is my PMag but thats no big deal.
"Hey I'm the first one to say its a great country but its a straaaaange culture. This is a place where gun store owners are given a list of stolen credit cards but not a list of CRIMINALS and MANIACS. And now they're thinking of banning toy guns...AND THEY'RE GONNA KEEP THE F**KING REAL ONES!"
-George Carlin 1937 - 2008 (RIP buddy)