.Just sorted out an MGI Military conversion & Pro-Mag UZI mags.
MGI has a relatively inexpensive .45 blow-back conversion bolt and barrel.
It is intended for use with their somewhat expensive (back-ordered in .45) modular lower.
This is a nicer conversion than the Olympic version as it does not require the installation of their funky ejector into the upper.
The upper can remain completely stock, no mods required beyond putting on a .45 MGI barrel.
Other .45 barrels MAY work, an Olympic will not.
A gas deflector and short dust cover are nice if you are not changing caliber often.
Of course the big hassle with .45 AR conversions has been the magazine.
Several companies make dedicated lowers, using Grease Gun or Glock magazines.
So far as I know the MGI bolt and upper should work fine with them.
I have now confirmed that it is very possible to use Pro-Mag .45 UZI magazines in an unmodified AR lower
I used a common 9mm Colt adapter, MGI bolt and barrel.
The Colt mag adapter needs only a very little modification, which does not prevent it still being used in 9mm.
Last shot hold-open is lost, but can be restored for 9mm.
The Pro-Mag UZI .45 mags tend to be a somewhat tight fit, but that is easily corrected.
The biggest issue I ran into was that the bolt was reluctant to close fully on a loaded round.
I traced this down to the MGI bolt's extractor not having enough clearance to ride over the cartridge rim.
Since extractors are much less expensive than MGI bolts I chose to modify the extractor, I can modify the bolt later if the extractor turns out to be weakened.
I ground down the back side of the extractor with a curve until it had enough movement to snap over the cartridge rim properly.
As installed the square edges were bottoming out in the extractor hole, the extractor appears to be a standard 1911 part with a relief ground in the outside edge, or a very close clone.
Now that this is sorted my next step is threading the barrel for my FIDO .45 suppressor.