Aside from the Bulldog Tank, a few other overly sized tanks, the
King Crab, there are very few if otherwise no other mechs who use the single shot 203mm Devastator AC/20 variant, and the
Cauldron Born (who has a UAC/20 version of it), none of the other mechs were considered stable enough to effectively use the Devastator AC/20 variant (the only singleshot in battletech lore/fluff) without significant loss of balance (falling over). Now you notice the shape of those two mechs? They are very low to the ground, very long, very wide, very stable. Unlike a Jagermech, Atlas, etc., which are kinda wide but not really, very tall, and certainly not the most stable things in the world.
The Atlas and a few others could safely use the next largest variant, the Chemjet Gun which (depending on the version) is either a slow-firing 3 round burst (burst-variant), or a steady firing 1 shot every 1.67 seconds for 6.7 damage ('Auto-fire' variant, no actual cooldown time aside from the space between shots. Accomplishes slightly better dps than the single shot in its current form).
As the mechs got smaller, the AC/20 reduced in caliber.
- The Hunchback is typically depicted as firing 4 (various artwork) to 5 shots (see MechCommander intro) for its AC/20 to deal the full 20 damage. As a note: Typically the Hunchback has the Tomodzuru Autocannon Mount Type 20 (which though not listed on Sarna is fluffed to be a 4 shot AC/20 -- basically a burst or slower auto-firing AC/5 in a 14 ton form - MechCommander gave it a burst form and since it is not listed as having variants of this variant, one can assume it does not have an automatic form [otherwise it'd be a 1 shot per second AC/5 for 14 tons which is slightly faster than the macro-unjammable UAC/5). The one in the MechCommander intro has a Defiance Mech Hunter AC/20 (which is a 5 shot with softer recoil).
- A Raven 4X could mount an AC/20, but it would be of the same caliber as the AC/2 in the form of the Crusher Super Heavy Autocannon 20 which is a rapid 10 shot burst or semi-rapid auto-fire (there's 3 different manufacturing companies on 3 different planets of CSHAC/20 listed, which would have theirs varied enough to compete with one another). Higher calibers would not actually be safe to mount due to recoil and the light weight of the battlemech.
- It should be noted that in practice, the higher the caliber of cannon mounted on a smaller platform, the more intense the recoil becomes. Braced or not a Raven 4x firing a Devastator single shot AC/20 would find itself flying through the air as its on-ground surface area is far too small and the cannon is far too high (picture firing a destroyer's cannon from on top of a tower supported by two feet each barely half its width and thin legs.) In fluff the Atlas must be braced before attempting to use one, and even then lost its balance, dooming the weapon to never be mounted on the Atlas by any sane engineer again.
Just to note: This is a 203mm cannon. This is what the Devastator AC/20, and thus the AC/20 we have in MWO, is supposed to be.
In comparison this is an Abrams M1 tank. (which according to Wikipedia, has a 120mm cannon -- the AC/2 in its current form is supposed to have a 150mm cannon).
So,
yeah.
This 155mm
artillery cannon is 5mm larger than the Crusher Super Heavy Autocannon's caliber, and thus 5mm larger than the AC/2.
This is 10 mm "less" cannon than the Chemjet Gun AC/20. Notice the massive rear brace, and the very low profile of the cannon. If mounted on two legs and hung as high as a Jagermech the Jager might actually have to slow down slightly while firing the Chemjet Gun.
Think about this for a minute... Shouldn't these be suffering somewhat stronger recoil, particularly the 203mm AC/20 which has a barrel more commonly mounted on destroyers and battleships? Granted, the Devastator in MWO's current form is severely snub-nosed significantly reducing recoil and thus its range, it should still not be 'non-existent.'
-------------------
That said, since most of what I've said here is about autocannon variants, I
made a video demonstrating the Crusher SHAC/20 and two versions of a Burst Fire variant Chemjet Gun.