I have an upper receiver cut for 450 Bushmaster (slightly enlarged ejection port) that I no longer need to use for that caliber, so would it be fine to run 5.55 NATO instead using that receiver with the proper barrel etc?
I’m thinking it should work fine as it’s just a standard AR upper with a slightly larger ejection port cutout.
Am I missing anything, or am I just overthinking it?
Attached FileI’d prefer to keep it for a build as the fit is perfect on every lower I have, but I could trade it for a comparable upper.