Lasers: Technically, lasers should have an effective range somewhere in the vicinity of the horizon. With the sort of targeting tech that already exists, it is possible to hit targets over the horizon, so (barring urban combat) you will primarily be shooting at targets too far away to actually see - you'll just be firing by radar. In fact, your skill won't even matter - the computer will have to do all the targeting for you to score a hit. Again, you can't see the target, so there's no way you could aim for yourself.
Missiles: SRMs are roughly analogous to modern TOW anti-tank missiles, as far as explosive power and size go. Assuming they have the same fuel capacity of a TOW (reasonable, considering the fact that 'Mechs - much larger than most modern TOW-equipped vehicles - should have no problem carrying plenty of missiles of that size - although, again, this assumes that the 31st century has brought no advancements in fuel efficiency). So, their effective range should be about 3.75 kilometers - probably outside visual range, unless you have some very good magnification systems. LRMs, meanwhile, seem to be analogous to the modern AIM-120 AMRAAM - a missile specifically designated as being intended for use on targets beyond visual range, carrying less explosives but a lot more fuel than the TOW. Assuming that LRMs are of the same size and explosive power, and that neither explosives nor fuel have become more compact/efficient by the 31st century, the maximum effective range should be around 70 kilometers (at which range it can at least hit near enough an 18x13x5 meter airplane [using the F-22 Raptor's specs] traveling at supersonic speed to crush the jet with the shock wave and riddle it with shrapnel - assuming the missile doesn't hit directly. Since 'Mechs are much slower than a jet fighter, odds are that the missile would be able to score a direct hit). So, yeah, have fun shooting targets that aren't even on your side of the horizon. This is an even more obvious case where the computer would do all the aiming - the pilot would just sit there and wait for the "fire now" message. LRMs would most likely be the most effective and widely-used weapon around, due to their over-the-horizon capabilities and their guided nature (allowing them to adjust for course changes on the target's part)
Autocannons: These would be the shortest range weapons in the universe, if they are anything like their modern counterparts. The 25 mm Bushmaster autocannon (about the same as the smallest Battletech autocannon would be) has a maximum effective range of about 3 kilometers - yet another weapon firing far beyond visual range (barring the use of the highly sophisticated magnifiers that would probably exist in the 31st century). The 8"/55 caliber (203 mm) naval gun (the newest direct fire weapon I could find in the 200-250 mm caliber range), which would be about the high end of caliber as far as a 'Mech-borne autocannon goes, has a maximum effective range of about 27 kilometers.
Gauss Rifle: The U.S. Navy, as of 2008, has a working prototype of a railgun (basically a gauss rifle). Predictions for its final performance have it accurate within 5 meters (about half a 'Mech's size) at around 370 kilometers. Granted this would be reduced against a moving target, but the potential is there - and keep in mind, despite what we are assuming for the purposes of this post, there would probably be highly advanced (and compact) ballistic targeting devices in the future that put modern supercomputers to shame - the only possible problem would be if the target decided to change course for some reason. Of course, that's what LRMs are for.
PPCs: Yeah, for obvious reasons, I could not find a real life analogue for these. Nor could I find any mention in the canon about what their theoretical range should be without the horrible targeting systems used to explain the very short weapons-ranges. So, I can't tell you what they'd be like in a game incorporating them as realistically as possible - sorry.
Now, the ballistic weapons (gauss rifle and autocannon) do have one major issue - time-to-target. Their effective ranges may be dozens of kilometers, but that's only going to be ideal for stationary or slow moving targets (probably most assault 'Mechs), since a fast target would be out of danger by the time the projectile hit. Of course, even modern targeting systems can calculate ballistics in real time, adjusting for gravity, changes of angle in the firer, velocity of both target and shooter, and so on - just look at the systems used on jet fighters to help aim their guns. So, it's entirely possible that hits could be scored at beyond-visual ranges even on fast moving targets, assuming no change in course. Then again, even the smallest of the ballistic weapons mentioned here have a fair amount of splash when they hit a target - and let's not even get into the 5-inch and the railgun. So, even if the target changes their course, they are by no means guaranteed to be safe.
So, basically, aside from urban combat, we should realistically not even be able to see who we're shooting at. In the cities, we would of course be able to see the enemy, allowing us to have the exciting, brawling combat we see in the TT game and other video games. But do we really want a game which consists entirely of urban combat, nullifying most (if not all) of the lighter weight classes' speed advantage? Or a game where we can't even see who we are shooting at? I think not. So, let us keep the absurdly short ranges that will allow all types of maps to be fun.
If I made any errors, or if you feel like weighing in on the issue, please feel free I'm not perfect and probably made some mistakes here, and I'm sure plenty of people have some opinion on this.
Edited by irishwarrior, 14 November 2011 - 05:12 PM.