Weapon changes?

[Solid Spartan]

Was the reason for all the fake names in MGSV just down to licensing?

Fake designs, too. None of the guns in MGS5 are real. And yeah, possibly. Assuming Kojima didn't go balls to the wall and do it without permission, the Glock 18 and HK weapons in MGS4 probably cost a pretty penny.

It never even occurred to me that guns are IPs that you’d need to pay to use the likeness of. Do they eventually become public domain designs or is that not a thing?

In most cases, just changing the name and/or altering the design in some fashion, whether obvious or not, gets around it. The patents for the AR-15 are public domain; only the name "AR-15", patented by Colt, can't be used. The M1911, AK-47/74, and most vintage WWII and older arms are public now. The technical design specs for the M16 family, M4/M4A1, M249 series, and some others are owned by the US government, and so are public domain. Colt tried to sue over the name "M4" (the "M4 Custom" name could have been enough to skirt it, since said lawsuit was still in progress at the time of MGS4's release), but the suit was struck down. And looking up the details of Glock's trademarks, it seems to be a complicated yes and no. Older versions, like the Gen 1 and Gen 2, would theoretically be public domain, but that could be argued because Glock is continually making improvements to the basic design. IDK, trademarking/patenting/copyrighting are far too complicated for me, which is why I never went into that job line lol, so this is all to the best of my knowledge.