The proliferation of sophisticated weapons systems during the so-called "Dark Age" that began in 3132 and continued throughout the IlClan era made it very difficult for even wealthy powers to maintain a qualitative edge of any sort over their opponents. As the leading cause of this proliferation of sophisticated weapons systems, Clan Sea Fox was keenly aware of the problem and pooled the collective R&D resources, as best was possible, of their scattered khanates together to come up with exclusive systems that might give them some (temporary) advantages.
One of the most promising avenues of development was further elaboration on the rotary autocannon concept, as they had managed to successfully copy, and arguably eclipse the original Federated Commonwealth weapon concept. A number of approaches were tried.
Simply speeding up the rate of fire of the weapons proved too difficult. Linear increases in rate of fire lead to polynomial increases in the stress on the reciprocating parts, and the scientists assigned to the program found that there are hard limits on how quickly autocannon ammunition can be handled before it starts distorting or even falling apart. A monstrous RAC-10 was trialed, but again, difficulties in handling such large ammunition so quickly meant that the weapon was atrociously unreliable. There was some success with an extended-range RAC-5, which sported longer barrels, but the increased mass of the barrels meant that the spin-up time and therefore responsiveness of the weapon was never satisfactory.
The scientists quickly concluded that such brute-force approaches would not work, and that some sort of synergistic combination of concepts was needed. They quickly settled on a rotary autocannon firing caseless telescoped (CLT) ammunition. The prototypes proceeded through development smoothly, and the weapon was duly christened the CLT-7, as marketing objected that "CLT-RAC-7" was too much of a mouthful, and the Sea Foxes were going to sell this thing eventually.
Instead of conventional cased ammunition wherein a metal or composite case holds the propellant and projectile, caseless telescoped ammunition buries the projectile inside of a block of propellant. This configuration is much lighter, and more importantly is much more compact, allowing somewhat higher caliber rounds to be fed through the mechanism without fear of excessive reciprocating parts velocities or ammunition delamination. Additionally, the savings in ammunition weight could be traded in for denser projectile materials. The development team was ultimately successful in reining in the problems that Inner Sphere scientists had encountered with both caseless and armor-piercing ammunition.
Rules
Type: Ballistic (Direct, Rapid Fire)
Tech Base: Clan
Year Availability: 3154
Heat: 2/shot
Damage: 7/shot
Minimum range: none
Short range: 1-6
Medium range: 7-12
Long range: 13-18
Ammo per ton: 14
Tons: 12
Critical slots: 9
Each hit automatically rolls on the determining critical hits table with a -3 modifier, as per standard armor-piercing ammunition rules. This effect is negated or modified by all armor types which affect normal armor-piercing autocannon ammunition. The CLT-7 does not suffer from an additional +1 to-hit modifier, however. The CLT-7 also does not suffer from the critical failure problems of normal caseless autocannons. The clan scientists know what they're doing and they took care of all that janky nonsense. The CLT-7 has a maximum rate of fire of 6 rounds per turn, and jams and unjams per standard RAC rules.
(Out of universe commentary)
I think this is reasonably balanced by Dark Age standards. It's the size and weight of a clan-spec LBX-20, and has 50% more range. If you turn the rate of fire dial up all the way, it has very slightly more expected average damage than an UAC-20, but the hits do one third as much damage each. Each hit has a 5.55% chance of auto-critting, which is not terribly high, and because it's using the same modifiers as an AC-5 firing AP ammo it can only crit a single location and can't amputate limbs.
Low-caliber ACs firing AP ammo suck. The math does not lie.
This means that even on a full 6 round burst where all 6 shots hit, there's about a slightly less than 71% chance that the weapon doesn't get any autocrits whatsoever. Conversely though, on an average cluster hits roll of 4 for a 6 shot burst, there's a slightly better than 1/5 chance of getting at least one critical hit, so the effect isn't negligible and does make the weapon meaningfully more scary. Of course, for the full 6 shot special you're paying ER large laser heat and a 1/6 chance of jamming.
