Besides the training scene in BoK, you also had the Nova Cats going . . . against the Alshain Avengers IIRC in Path of Glory.
Another one folks are forgetting is from Initation to War where Count Shu's (regional noble) roughly mech battalion had umpires in the mechs for training exercises, that part of the story pivots around when a umpire was tampered with resulting in a training death (and yes, they happen outside of Clan training. Supposed to be some interesting comparisons pre-Afghanistan.) because the weapons went off.
Let's look at this from a complexity angle . . .
Simulators are expensive up front, but easy because all you have to do is plug things in and have power. The real question is how much/well they simulate. Apparently CapCon arcade mech simulators are good enough to create troops . . . Sim pods are for force on force engagements.
Next step up are training ranges which run the gamut from gunnery practice, (for mechs) mounted land navigation, tactical gunnery practice (pop up targets, movement through a course), familiarization/scenario training, and finally force on force.
Gunnery practice would be the simplest . . . walk through a series of bermed areas and light up targets, scored based on accuracy and speed. Typically you would not be going full speed (for this purpose, 'tactical') so part of the purpose would be maintaining the feel for firing off the cannons and missiles as your mech rocks. The restriction here would be X number of targets and Y number of shots with some targets playing with the time to improve your score, or navigation gates (like skiing & kayaking) that will penalize you with time. Fancier versions get more like the Olympic biathalon where you race between shooting points, have limited shots at each point, and take time penalties for missing.
Mounted land navigation . . . well, trooper, bad news is the enemy took the sats down and your commo is being jammed . . . and it if was not being jammed, it would let your enemies close in. Well! Lookie there, your ticket off planet is over there . . . 40 hours away, you have 44 hours to make it . . . and watch out for bogies. OR Troop, you are going to be one of the mechs we are infiltrating through enemy lines to execute a flanking attack. Now the crunchies have found a way through the enemy's LPOPs and remote sensors, so here is the map loaded in your system and you need to hit these check points on a timed schedule while avoiding the patrols which are also noted in your nav system. This sort of training would be easier for mechwarriors with natural grace & terrain master SPAs.
Tactical gunnery practice would be more like what Kai went through . . . moving at combat speed & discipline, there will be pop up & moving targets that are gauging your response time against accuracy. Targets activate and deactivate through either they being hit or timing out. Some of the targets being presented test decision making- do you hit the Hetzer that is closing or the LRM Carrier currently raining fire on you? Depending on the course you could integrate defensive drills with your runs, scoring could reflect how much you leave your mech out to be hit while you engage.
Scenario training is where you would be practicing certain tactical environments- this is what happens when a lot of Army units are 'in the field.' They have a scenario (my command loved to have us being invaded from Orangeland in the North using a bunch of Chinese & Russian gear . . . ) either for your part in a big conflict or a small action- for mechs or armor it could be escorting a convoy. Your company is escorting a convoy to a forward unit trying to push through enemy lines and the area is not secure which is why you are assigned. The company commander has established a escort formation (part of their practice & eval) and is calling in as the convoy progresses through the checkpoints . . . when BAM! AMBUSH! Company commander orders the convoy to either speed through while mechs lay covering fire and call for artillery, airstrikes and VTOL coverage per doctrine. Or a patrol . . . when BAM! AMBUSH! Near or Far? Near? Well you better hope that butter bar remembers you are supposed to assault through and gives the right order . . . all 12 mechs go charging in the ordered direction, firing blanks off at the 'enemy' position.
Then you get the MILES like umpires discussed in a few books like Initiation to War- or for the Clans just power things down a bit. It is like the above but it combines everything . . . sort of hard to tell who you 'killed' when using blanks, but here we are looking to see if you can pull off the right responses to tactical situations with accuracy in your weapon's fire and smart decisions to protect your mech from fire as much as possible. Closest you are going to get to full combat, better than even the most accurate sim pod.
One thing ALL of these besides the sim pods require is LAND . . . lots and lots of land, usually land no one wants is what is used. The larger the unit you want to operate together, the more land you need- it is also not straight arithmetic. A battalion will need more than 3x the land a company would to operate on- partly b/c you rotate where troops operate so the land recovers to maintain it's 'wild' status. If you look at it in the US, it is why most of the armor and wargame training areas are out west- Ft Irwin in the Mojave Desert is 1000 square miles which tests units before rotations, Ft Hood has 214k acres for armor training, or Nellis AFB which hosts Red Flag (and thinking about it, is something like the Martial Olympiad for US & ally air forces).
Some of the older US bases also have 'no go' areas . . . which are where explosive shells, rockets and missiles are fired for live fire exercises. You do not go there b/c you never know that all the munitions exploded. Basically a BT base would have to plan on areas that will never be entered w/o being led there by EXO units (huh, we need a EXO IndiMech) . . . or is it UXO, been a while since I sat through one of those classes.
Now we DO get a few places that mention this sort of thing. One that springs to mind is Small World. The Chaos March SB said Duke Small had rented a lot of his planet's arctic regions to the AFFC for winter training. Have to wonder how often formations rotated through the camp/training grounds though I would imagine they were a Sarna March asset . . . MABYE some Capellan March troops went there too from the Terra-ward zones. Outreach has training zones for merc evaluations and the Dragoons have their own reservation on a whole other continent. We get a bit about Kathil having training areas before the FCCW kicked off there- the Kathil CMM was using it and so was the NAIS Cadre on that planet. I would imagine each major mech industrial world with a major on planet garrison has a large training range, both for the garrison and for the company to test their products.
