Manufacturers do things to FORCE you to buy their casing and their loads.
However USR (the one company with permits yet is not certified) (the one manufacturer that honors the ATF exemption law 27 CFR 555.141-a-8 to the letter), makes casings that are compatible with AT, and closures that are compatible with AT, and loads that are compatible with AT, and loads that are compatible with Irvine/Kosdon/Kosdon East/AMW/EX snap ring cases.
If you use USR cases and loads in unison you are rewarded by fewer leaks, more reuseability, far easier reloading, and better fit but you are NOT FORCED.
Despite the massive legality they are agressively blackballed by NAR and TRA.
Good thing that only limits 5000 of the nation's 1 million rocketeers, eh? Many of whom are armchair rocketeers, Aerotech employees and investors, people with permanent grudges and rmr lurkers :)
NAR and TRA are religiously opposed to open systems.