I think the name AR-15 is long over its copyright (1959) if in fact it is not a public domain from the government contract (originally the first M-16 model was simply called AR-15, it didnt have a forward assist which the M-16A1 later included). Colts copyrights are under specific models names, not generic rifle names covering an entire design such as the AR-15 rifle system.
After all Armalite sold the rights to Colt way back when but sells Ar-15s now. Bushmaster has been selling them for over 30 years. The subject of the copyright suit was over the military designation M-4 which is a public domain, and cannot be copyrighted. Colt lost that suit hands down and had to pay for Bushmasters legal defence for the lawsuit in turn.
Specific companies use specific names for their exact product that they sell, not AR-15, etc. (Examples, sr556,mr556, A-15, R-15, xm15e2s, etc....). These companies can use for specific model or designs the name M-4, etc (public domain) although some companies choose to use different variations such as AP-4, etc