The fact that 450 Bushmaster mags can and have been successfully used in the 30 Remington AR has been claimed for some time. Looking at the two side by side, the differences are very obvious. Truth be told, the 30 Remington AR specific magazine looks crazy but works great in the 450b as well. It actually cycles smoother than factory 450b or DIY 450b magazines in the 450b.
Here's some insights into whats critical about getting the 450b mags to function. Nothing! If you try to pull back the 30RAR bolt with a 450b mag in it, your experience will vary from no big deal, to a slight hitch as you pull the CH back, to it stops dead in the water about 1 inch back. It depends upon how tight your mag fits in the well and how high it rides. This is a game of about .050 clearance making all the difference in the world.
The 30RAR uses the larger AR10 type bolt modded to fit in a conventional AR15 carrier and an AR10 barrel extension modded to fit on an AR15 profiled barrel. The AR10, being more powerful, both of those components are larger, especially the bolt lugs. They hang down further than an AR15 bolt lugs. One of them catches on the front lip of the magazine follower. DPMS' solution was to bevel that portion of the follower edge, among other changes to facilitate operation in the 30RAR.
Here's a look at the bevel as implemented by DPMS:
I tried to catch the light reflection to emphasize the bevel.
Here's what happens when you use a factory 450b MAgazine in the 30RAR, unmodified:
It looks worse than it is as the displaced portion of the edge is hanging in the picture. It is important to emphasize that the ding will vary depending upon how high your particular magazine rides.
Corrective action: None if you don't mind the ding, the bolt being steel, will win the battle after a few shots. You can however take a swipe on that corner with a file and problem solved.
It has no affect on operation in the 450b.
Here's a rare, amateur video glimpse of the elusive Hoot'ster caught in the wilds of Minnesota:https://youtu.be/3eDsB9WPn4I
OOPS! Darn brass catcher jammed it up!
Take 2: Minus the brass catcherhttps://youtu.be/k18JrAaiG6s
That was only 5 rounds, but at a buck twenty five a shot, that's all you get.
Did you notice the leaky gas block? Thanks DPMS.
So drop your floorplate, grab a file and enjoy the additional capacity and readily available supply.
Hoot's Tip: while you're in there snip off some of the overkill spring. You don't really need that much upward pressure. Might as well iron out those capacity limiting tabs while you're in there as well.