[Targan]

There is scope for nearly infinite variety of opinion on this topic but realistically can be broken down into two main ways of looking at the issue:
1: Entirely factual, where you simply find the real life information on when a given weapon system was fielded and apply that to the T2K timeline or
2: Assume that the differences between the IRL and T2K timelines resulted in various weapon systems being developed and/or fielded earlier, later or not at all compared to RL.

In nearly all cases IMTW I take the latter view, and more specifically that because the Cold War never really ended in the T2K timeline the development and fielding of many weapon systems was accelerated. I think an acceleration of three to five years is not unreasonable in most cases but there are many exceptions. For instance, the development of some weapon systems may have been directly or indirectly influenced by advances in materials technology and those advances may not have been influenced by whether or not the Cold War continued (such as some developments made in the civilian sector that were not initially military in nature). The time scale for the application of such developments in the area of weapons tech would therefore be similar in both the RL and T2K timelines (although the fielding of the resulting weapons systems could be accelerated or decelerated in T2K once they had been developed).

The above probably isn't very easy to read but I think you all will get an idea of what I'm trying to say.

Relating this to Raellus' opening post with the UK as an example I think that the L85, L85A1/SA80, SLR, and Armalite AR-18 could all be used by British forces during the Twilight War, but the L85A1 might have been seen in only limited numbers because if you apply my suggestion of an acceleration of three to five years to Raellus' statement that "the improved L85A1 version only entered widespread service right around 2000", it would only have entered widespread service in the T2K timeline somewhere between 1995 and 1997.