I'm not a conspiracy theorist. I chide folks I work with who are.
We all know that manufacturing tolerances vary from one unit to the next. Reamers wear. Custom parts suppliers can't always keep up. Close, but not exact substitutes get used. When your phone is ringing off the hook from hungry distributors and you can't get enough custom bolts or custom extractor hooks to even come close to ratcheting up supply, maybe you settle for ones that are looser toleranced, or ones for a 7.62x39 instead. Maybe you produced higher quality assemblies early on to develop a demand base, only to discover that the demand snowballed until you can't keep up, based on the quality standards of the early units. Maybe maybe maybe.
For the few folks who have tried .284 brass, I suspect if polled, they would report surprisingly different results. Not because they got up on the right or wrong side of the bed. Not because they used the wrong techniques. Not because they started with out of tolerance brass, but because not all units were created precisely the same, especially once the sales department was screaming on the phone to the manufacturing department. I sincerely believe these different results speak volumes. Bushmaster is not designing the 450b to work with .284 brass and Hornady is not producing brass with the same rim, extraction groove and wall profile as the .284. Getting the two twains to meet is as much luck and art as it is precise workmanship and raw materials that are to spec. If you take a new Hornady 450b brass and it fits in the chamber fine. Then you seat a bullet and it fits into the chamber fine. Then you take a piece of cut down .284 brass and it fits fine. Then you seat a .452 bullet and it doesn't even come close to fitting in the chamber. Then you squash the bullet by squashing the brass to make them fit. Then you are bandaiding the problem, not solving it.
I referenced this image a few posts back. Look at the bulge. That's not just bad luck.
After sizing the outside of the cases down to where they would thunk, the pulled bullets from those cases measured .444-.446 OD. That is not my idea of a recipe for accuracy or repeatable results, even with the small amount of obturation from a copper jacketed bullet, when going down a .452 grooved bore. That's approaching a musket.
Hoot