[buckeyevet]

Is it possible to use another caliber upper on a 22lR lower? Also if the lower is marked as 22 lR only, is it correct that a bullet button is not required?

 

[Combat Diver]

If the lower specs out to be a real AR15 then yes. Which lower are you refering to? The .22LR rifles from Smith and Wesson and Colt use different lowers and uppers.

CD

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[Big Bore]

Is it possible to use another caliber upper on a 22lR lower? Also if the lower is marked as 22 lR only, is it correct that a bullet button is not required?

I assume you are from CA? I don't know if the .22 LR complete rifles use standard lowers or not, I know you can use a .22 LR upper on a standard lower but these .22 LR ARs being built sold by Colt... I know nothing about their lowers. I am pretty sure though that they do not have a recoil buffer or buffer spring in the receiver extension, so you certainly could not use a standard AR upper on them unless you added a buffer and spring, which if it is that easy I doubt they would be allowed in CA.
However, it does not really matter what is marked in caliber on the lower. IF you can put a standard AR upper on one of these .22 LR lowers, and IF you can add a buffer and buffer spring in their buffer tube (receiver extension), if you used a standard mag release you will have created an illegal assault rifle if in CA. In CA you must use a bullet button mag release or they consider the rifle to have a detachable magazine and if in a center fire caliber that would be illegal, regardless of the caliber marked on the lower.