The mag body is physically longer to hold the additional rounds. It has a new floor plate that incorporates a sleeve to cover up the excess length that sticks out of the grip.
Posts: 3465 | Location: South FL | Registered: February 09, 2007
The purpose of that longer sidewall on the mag baseplate is to prevent over-insertion.
I haven't seen it happen, but others have reported it: particularly when inserting a magazine with the slide locked back, if the magazine passes the mag release when it's rammed home, it can bend the ejector.
The ejector on the FCU is integral: it can't be replaced. Bend that, and you're looking at a new FCU. You can bend it back, but it's going to break. If you seat a magazine with the slide off and look at how close the magazine comes to the ejector when fully seated, you'll see why it doesn't take much more insertion to bend the ejector.
The downside of the plastic baseplate is that it's not really durable if you're doing a lot of mag changes over hard surfaces; they ding up and get damaged relatively easily. There are replacements available, but none of them are designed to extend up the sides of the magazine like the factory baseplate (which works great with the factory mag well, too). Consequently, the aftermarket baseplates do allow for overinsertion.
I have a dozen or so 21 round magazines with metal baseplates; its important to be careful inserting them.
Youc an also run 17 round magazines with aftermarket baseplates; I have a bunch of 17 round magazines wearing the Taran Tactical baseplates, and those work fine, too. They'll always have a weak spot where the mag body meets the baseplate, but thus far it's not been an issue. I get one extra round that way. The expense is more than a factory 21 round magazine; the factory mag runs 45-49 bucks. I can get a factory 17 round mag for the same, or an ACT-Armscor mag for about 22 bucks, then add a 40 dollar baseplate.
