... A gun that fires a 125 KG slug at Mach 4 is going to generate a shitton of recoil.
So for me, IMHO:
Recoil for the sake of realism: don't care. We ignore realism all over the place.
Recoil for the sake of making a weapon 'feel' big an epic when fired: Go for it. (But game balance trumps all)
YES. Exactly! We know railguns make recoil . In point of fact, it's retarded to even think ANY battlemech, standing on two stupid ungainly legs as they are, could EVER even FIRE an AC/20 (much less take a hit from one) and remain standing. Too many of our players want it both ways: they want everything to be EXACTLY like it is in CBT, AND they somehow want us to work in a realism factor that was never present in any meaningful in CBT.
Just FYI: when an M1A2 fires its 120mm gun the whole thing rocks like a boat in a gale. It might not look bad in videos but it's definitely something you notice from the inside. It's not quite as bad as the sway from slamming the brakes on, but I had the recoil knock my helmet against the driver's night sight a couple times, and that's with the tank stopped, me sitting in a recliner, and the sight 6" away. We can't simulate the punch-to-the-plexus, ears-almost-popping pressure change that happens inside the hull, either. And a 120mm gun equates to, what, an AC/5 or /10 in CBT? Adding a bit of recoil for the bigger guns in MWLL would give you at least a taste of that action.
Edit: and that 95% missing statistic sounds like BS to me; what I heard from some of the guys who were there was that they just shot all their rounds off after each engagement so they didn't have to do the paperwork of checking them back in. Not that you can believe everything a guy in the Army tells you, but it fits with the natural inclination to "streamline" processes that I observed in most combat MOSes. 
This sounds about right. I didn't have the time or energy to go research the real numbers, but something sounded REALLY wrong about his stats and I was hoping someone who had actually sat in an M1 recently might come to the fore. Your conclusion sounds consistent with the Army and the soldiers I grew up with, and seems a much more plausible explanation. If you don't shoot all your ammo, you don't get as much during the next disbursement cycle: ask any active US military personnel, they know - so does any Canadian who ever trained with the US Army and was surprised by the amount of ammo we waste on training when they usually get (got? has anything changed?) a few clips a year.
And yes, for reference, I know full well how much recoil an M1 experiences when firing that 120mm (yes, the equivalent of a mere AC/10), which is why I keep trying to point out that this is a GAME - heck it's not even a proper simulator - and you can't have it both ways. You simply cannot make CBT "realistic" because if you did, the vast majority of the premises CBT is based on would have to be disposed of, and you'd wind up playing WoT with lasers, pew pew pew. We balance for fun and playability, and the operative word here is "balance", with CBT being on one side and reality on the other, and we try and keep the pivot point of the whole equation in that delicate zone comprising fun, playability, ease of use as immersion.
I really don't have a problem with a little recoil screen effect for immersion after firing AC's, so long as it doesn't really affect my aim: there are enough factors involved there that make it difficult enough as it is, and I just don't see a reason why we should introduce a mechanic that will widen the gap even further between the average players and the very best.
Recoilless rifles aren't. And they work more like rockets anyway 
Yep, I've said this numerous times in the last few years on these forums and linked repeatedly to both articles on them as well as
Murphy's Laws of Combat where this is law #2. I'm all for doing everything we can to increase immersion and realism as much as possible, so long as it doesn't negatively (or seriously) impact the already delicate and WIP game balance.
There is, however, the LAHAT round:
http://en.wikipedia.org/wiki/LAHAT It would still generate some
recoil of course, though it can't possibly be anywhere near as bad as the 120mm itself.
(i.e. assume the mech is programmed to take the upcoming firing into account, brace for it as well as possible, and then quickly reorient after firing, much like a person learns to do with enough training/experience with firearms)
DING! Give the man a prize.
