How does the ar180 fit in? you mention near photos of the diffrent bolts shown.
what's common, didn't ar180 have 2 generations.
I love this since not an AR.
what Picton said, AR18 was full auto that was made as AR180 variant in semi only for civilian market.
To add, it's important to remember that Sterling Armament (which made AR18 on license from Armalite) is a different entity from Royal Small Arms Armories at Enfiled (which was tasked to develop SA80), kind of like Springfield Armory and Ruger, Haenel and Walther, same country but two different manufacturers.
SA80 was quiet literally a rip-off from AR-18, and by literal rip-off, I mean Enfield engineers took two AR18s, cut them up and made bullpups as proof of concept. This is one of the samples that was later refined into SA80. It's quiet lietrally AR18 with "Sterling" scrubbed off, a bunch of steel tack welded in and an external coat hanger linkage as a temp solution:
The notion that Enfield ripped Sterling/Armalite is a well known fact, that is never formally acknowledged by Enfield. I'm not sure that Sterling could sue, because technically it was Armalite who owned design, but did they had any patents in US as well as UK is another matter. Also Sterling was hoping to get contract for parts, which is a common theme with smaller manufacturers seeking a piece of the pie someone got a hold of.
SA80 mutated as time went by and revisions / improvements were introduced. AR18/0 still has a lot of commonalities with AR15, more than meets the eye, like some pin locations and distances for vital dimensions. Which parts of it were not reinventing the wheel, or which parts of it were that wheel is just the optimal shape for the task?
Here is the AR18 and SA80 bolts. The slight difference is the dwell time to unlock the bolt that was considered to be the cause of many malfunctions.