I got a couple of the black 450 magazine followers and used one of them to convert a 10 round Lancer magazine into a 4 round 450B mag. These appear to be good sturdy mags and have an all metal feed lip that is nicely spaced for the 450. No modification of the feed lips was necessary. I also like that the floor plate on the Lancer is particularly easy to take on and off. This mag is "smoke" color, but they also come in clear plastic or solid black.
Installation of the 450 follower was a simple matter of removing the original and snapping the new one in place along with two slight modifications:
1. The black follower had guide ends that were a bit of a snug fit for the Lancer mag so I gave it a little TLC with some fine grit sandpaper to true it up.
2. The front edge of the Lancer magazine is flat and it was necessary to cut a slight curve into it (similar to the Bushmaster 5 round factory mags)
A dremel tool was used for that modification and the edges were lightly deburred by hand with a small piece of sandpaper.
The modified magazine holds 4 rounds.....almost 5 will fit and I suspect it would be no trick to trim down the guides of the black follower to get a fifth round to fit in there. I didn't bother with that because I am content to hunt with four rounds in the mag.
I fired off about 30 rounds through the magazine without any issues and am very happy with this conversion. I will be using it to hunt deer next week.