actually everything is in the suttas and for the purpose of the answer Buddhism i equate with Buddhadhamma, not sure what meaning the inquirer imparts it
And how, householders, are there three kinds of bodily conduct not in
accordance with the Dhamma, unrighteous conduct? Here someone kills
living beings; he is murderous, bloody-handed, given to blows and
violence, merciless to living beings.
So, householders, it is by reason of such conduct not in accordance
with the Dhamma, by reason of such unrighteous conduct that some
beings here on the dissolution of the body, after death, reappear in
states of deprivation, in an unhappy destination, in perdition, even
in hell.
Saleyyaka sutta (MN 41)
one could be a Buddhist who got caught up in unfortunate circumstances where they are forced to use violence or a deadly force which they wouldn't use otherwise, but they'll still have to experience kammic consequences, which is normally birth in hell
such a kamma i think to a certain degree can be alleviated if the mind isn't clouded and blinded with defilements, first of all with desire of killing, at the time of its (the kamma) creation
Again, with sensual pleasures as the cause, sensual pleasures as the
source, sensual pleasures as the basis, the cause being simply sensual
pleasures, men take swords and shields and buckle on bows and quivers,
and they charge into battle massed in double array with arrows and
spears flying and swords flashing; and there they are wounded by
arrows and spears, and their heads are cut off by swords, whereby they
incur death or deadly suffering.
Now this is a danger in the case of sensual pleasures, a mass of
suffering visible here and now, having sensual pleasures as its cause,
sensual pleasures as its source, sensual pleasures as its basis, the
cause being simply sensual pleasures.
Again, with sensual pleasures as the cause, sensual pleasures as the
source, sensual pleasures as the basis, the cause being simply sensual
pleasures, men take swords and shields and buckle on bows and quivers,
and they charge slippery bastions, with arrows and spears flying and
swords flashing; and there they are wounded by arrows and spears and
splashed with boiling liquids and crushed under heavy weights, and
their heads are cut off by swords, whereby they incur death or deadly
suffering.
Now this is a danger in the case of sensual pleasures, a mass of
suffering visible here and now, having sensual pleasures as its cause,
sensual pleasures as its source, sensual pleasures as its basis, the
cause being simply sensual pleasures.
Mahadukkhakkhandha sutta (MN 13)
When a warrior strives & exerts himself in battle, his mind is already
seized, debased, & misdirected by the thought: 'May these beings be
struck down or slaughtered or annihilated or destroyed. May they not
exist.' If others then strike him down & slay him while he is thus
striving & exerting himself in battle, then with the breakup of the
body, after death, he is reborn in the hell called the realm of those
slain in battle. But if he holds such a view as this: 'When a warrior
strives & exerts himself in battle, if others then strike him down &
slay him while he is striving & exerting himself in battle, then with
the breakup of the body, after death, he is reborn in the company of
devas slain in battle,' that is his wrong view. Now, there are two
destinations for a person with wrong view, I tell you: either hell or
the animal womb."
Yodhajiva sutta (SN 42.3)
one who is a Buddhist serving in a military during peace time with intent to slack on his duty at the high noon in favor of his obligations as a Buddhist, i think would be committing verbal misconduct of lying
Here's how Ajahn Sucitto of Cittaviveka Vihara describes his encounter with road bandits while on a pilgrimage in India
Then everything blew up. Nick turned round with a menacing expression
on his face; someone was tugging my robe on one side while the first
man was hauling frantically at the mug on its strap on the other.
Three men charged at Nick who was crouched boxer-style; he wheeled and
hit them with his backpack, then ran off with the three of them in hot
pursuit. I was being lugged in two directions simultaneously by the
strap on my water bottle and on my bag, I could only try to get the
stuff off and let them have it, but their pulling on it made that
impossible. We were going round in circles, with their excitement
spinning into frenzy . I had to stop this. “Wait! Wait! Let me get
this stuff off !” Momentarily they stood still. They all had axes and
staves. The leader glared at me through twisted features and raised
his axe.
Funny how your mind goes clear when the options disappear. Why
struggle against the inevitable? The only freedom was to go without
fear. I bowed my head and pointed the top of my skull toward him, drew
the blade of my hand along it from the crown of my head to the brow.
“Hit it right there.” Something shifted; he backed off, waving his axe
and muttering angrily. I stepped forward and repeated the action. Give
it away; let it all go.
Things settled. He lowered his axe. I slipped off the bag and the water
bottle and stepped back. The three of them began excitedly picking over
the treasure. I imagined that they’d rummage around, find there was
nothing there of any value, and run off. Two of them picked up the
gear and scurried down the track away. I felt shaky and sat down.
Better keep cool — I started chanting softly. Then Nick ambled along with a
smile but without his pack or assailants. “I’ve hidden the money;
Bhante, are you all right?”
His return signalled further frenzy. As his assailants returned, the men
charged at him with their sticks and began swinging blows; Nick caught
most of them on his arms: “ All right, all right! I’ll show you
where.” And the mob had streamed off into the forest by the time that
I got to my feet, leaving me with one lad, who sullenly resisted my
attempts to strike up a conversation. But he was mellow compared to
the older men when they returned — without Nick or the bags. They
jumped on me and pulled off the bag that I had around my neck
containing the relics and Buddha image; they ripped off the waistband
that was threaded through my pouch; they clawed under my sabong and
dragged the passport out of another pouch that was hanging around my
waist.
Then they were off with the loot tied up in bundles on their
heads. The leader turned round and said “Your bags are over there,”
pointing into the forest. “Fine, OK.” I said, in a vaguely warm way .
The forest went back to silence as usual ... a sunny day, with the
forested slopes on either side.
"Rude Awakenings" (pp. 238-239)
https://www.youtube.com/watch?v=r9YE1oP-qr0#t=1h1m15s