Of course there is no general rule for hex-to-meter formula, as we must take other factors into account like usage method, sighting and most importantly relative performance in cases when there must be a range difference between certain units.
I made a xcel table because the first time I wrote this post, all went lost...

There are guns which are not in the game. Either because I suggest their implementation (importance, gap fillings), or because that model better represents the weapons used. Also I brought them up for comparison example.
There are gun not included, either because I forgot - or because they are correct that way, similarly to another model.