For the good of the Order:
https://berettaforum.net/vb/showthread.php?t=86229
A report from 2012 on the compatibility of Beretta 81 (.32 ACP) barrel in a Beretta 84 (.380 ACP) gun.
Apparently you need the correct double stack mag for caliber.
I’ve tested the fit by putting an 81 barrel in an 80X and cycling dummy rounds through it.
Also a report on that forum that Allegheny Arms has threaded 81 (.32 ACP) barrels for sale.
I’ll put testing the 81 barrel in the 80X on my “to do” list…. After testing and chrono-ing various .380 loads, including some of my hand loads built for reduced recoil and some high-vel HP loads.
I also have a RDO plate on the way from Beretta, as well as a Holosun HS407K from Amazon.
Placed that order before seeing the report from @
R_Shackleford re: Beretta RDO plates for another RDS. I’m hoping I have a better result, otherwise I’ve wasted some money.