Yes.
After the early
90s. It does change rapidly.
Timeline on Sarna
Relevant bit:
'The earliest events distinct to the BattleTech universe occur after the end of the Cold War and the collapse of the Soviet Union. The
United States, Europe and Japan announced in
1994 their intention to jointly construct an orbiting industrial facility named Crippen Station, which was successfully launched eleven years later. A
1997 coup d'état by hardline communists restored a militant, Soviet-style government in Russia and sparked a "Second Cold War" with NATO that lasted until the start of peaceful reforms under premier Oleg Tikonov in
2005. The republic crumbled in 2011, igniting a civil war that drew in NATO and saw the successful use of the Western Orbital Defense Network (WODeN), successor to the earlier Strategic Defense Initiative, to intercept a preemptive Russian missile attack against western targets. The war ended with a
Western Alliance victory in
2014.'
The Cold War ended in December
1991. USSR collapsed, war was over. No major changes in the twentieth century until then.
This means that we had the same techbase until the end of the century. A lot happened in only
eight years.
Yeah, that's somebody on Sarna playing silly buggers with the timeline because they noticed it didn't match history but didn't realize it's an AU. The Soviet Union didn't collapse in the BT timeline.
At the beginning of the 21st century, life on Terra had not changed much from what it had been at the close of the 20th century. Despite attempts at reconciliation in the 1990s, the planet's two giant superpowers still opposed one another, but now their tangled web of weaponry stretched outward into space. Over the next 100 years, however, the situation changed dramatically. By the end of the 21st century, the people of Terra stood poised in apparent unity on the brink of their first expansion into the stars.
Politically, humanity's new age began in 2011 when the bloody Second Soviet Civil War tore that nation permanently asunder. As the Soviet strife threatened to bring the rest of the planet to the brink of nuclear war, a joint force of North American and Western European troops intervened to end hostilities in 2014. -Mechwarrior 2nd Edition, page 106
So in 2011 the Soviet Union was still around, and both it and NATO had already colonized space and heavily armed it before 1990.
So, what I got out of that was explosive rounds at .6kg over 10s will likely exceed 1 damage but end up rounded down to 1. Since .94 is with non-explosive ammunition, and being explosive is key in dealing damage to BT armor.
The conversion rules for weapons to BattleMech scale damage are on page 211 of
A Time of War. They are, however, exceedingly obtuse
even by the standards of BattleTech.
The key to doing damage with infantry-scale weapons is more hitting it many,
many times in the exact same spot in a space of milliseconds. The standard generic autorifle in the Warrior's Catalogue has a low damage of only 4B/4B, but a burst fire rate of 15 which translates to it doing 0.52 'mech scale damage, while the elephant gun, despite doing far more damage per shot, is incapable of burst fire and does an anemic 0.11. The bolt-action rifle can't burst but still can fire faster than the elephant gun and winds up doing 0.14. The TK Assault rifle has the same base damage as the autorifle but only fires 10-round bursts and winds up doing 0.44 on 'mech scale. Meanwhile, the clan Bearhunter Autocannon can do burst
90 with a base of only about twice an Autorifle (9B/8B) and hits for a full 3 'mech scale damage via throwing down 180 rounds per turn. This is, incidentally, 18kg of bullets.
Note also that the generic autorifle is tech level C if we still want to quibble about that.
And that means for 500kg I can probably do 2-4 damage with 1.2-2.4kg of ammo a round if I strap 2-4 M2s together. 500kg is at least one, if not 2 Oerlikon 20mm autocanno- sorry machine gun, at ~92kg a pop, plus all the bits and bobs you need it to be properly automated and ruggedized.
Actually, with 80kg of M2 (that's two), pretty sure I could build a rugged, military grade, quarter ton gun mount using 80s level machine shops and materials for a hardpoint given that HMMWV's have turrets that with a M2 mounted are only like 150 kg if my napkin math is right (The turret is ~200 pounds). It's not like it has to go 360 degrees, or be armored, like the HMMWV's turret. Need a semi decent cone for aiming, the gun end of the automated ammo feed (pretty sure that exists already so I don't have to try very hard), and maybe set something up to clear jams. That last one might take some thinking.
And I'm not very skilled at that kind of work. But that's clan tech weight and damage on a tech level of B, just not ammo efficiency.
Most of the weight has to be in the controls and ruggedization packages. Armor is counted on the mech. So any armoring should not be weighed against the machine gun... pod.
It's worth noting that all BT 'mech scale machine guns require a power source in order to fire, per TechManual page 228. This suggests that even the lightest machine gun requires significant power beyond just recoil for aim and possibly to cycle it much faster than mere gas pressure can manage. This jives with their huge weight which exceeds what should be reasonable, and also with the fact that rate-of-fire is so vitally important to raising an infantry weapon up to the threshold where it can damage a 'mech.
And naw, I'm not being too rigid about tech levels, FASA just had no fucking clue what they were doing with techlevels because they're all over the fucking place. Like most of their stuff. Their timeline is all kinds of fucking weird, for instance. How old was McKenna again when he did his thing? Like 19? 22?
Hmm? McKenna was born in 2274 and founded the Hegemony in 2314, at age 40. Unless you mean making the rank of Admiral, he did manage that at 21.
It is, however, canon. And using canon to avoid Loki's Wager is a good thing as far as I'm concerned.
I mean, if I was being too rigid about tech levels, you are being way too rigid about what makes a machine gun do 2 damage. Like it weight exactly 500kg. And using exactly .5kg of munitions over ten seconds.
How rigid are we supposed to hold to the rules? Because mechs have a nigh impossible density. And so many weapons have such shit range that we could pummel the fuck out of any BT force from far beyond their engagement ranges.
Pretty dependent on what you want. Per their canon policy, hard rules trump text and that's what I've been using here. Per the lore in the books, infantry weapons actually
can't damage a 'mech and things like machine guns that are man-portable are useless against them. It's actually a plot point in the second Gray Death Legion story that Grayson pioneers a technique using satchel charges to destroy a 'mech's knee joint, and everybody is amazed because it's common knowledge that no infantry-portable weapon can actually harm a 'mech. Grayson figuring out a way for infantry to even do scratch damage to a 'mech is considered so game-changing he's called the father of 31st century warfare.
So yeah, you
have to be attached to those rules at the hip, because the second you step away from the concrete game rules the machine guns don't scratch 'mechs, the Merkava can't scratch a 'mech, and per the devs on the official forums, even an Abrams' main gun is incapable of doing any damage whatsoever to a 'mech.
/shrug
Aiight.
But then, per the rules we can already build Clantech Machine Guns. And the ammunition needed to do 2 damage.
No, we can't build Clantech machine guns. Note that, as above, Tech Level B includes building at least orbital weapons platforms and most likely having a viable space navy. Earth in our timeline today is
far behind where BT is in 1990 when it comes to weapons and we can't build a lot of their Tech Level B stuff as a result.
Unless, of course, Bear Ribs is wrong
This requires far more suspension of disbelief than FASAnomics.