I'm curious as to the movie now.
But anyway, determining the capabilities of a weapon requires crunching a LOT of numbers, and your stats there don't factor in a lot of important details. Headshot multiplier, magazine size (and thus, single mag damage potential), and you're looking at their base stats rather than what you would get from the Sharpshooter's perk bonuses.
An unperked headshot from the LAR is 280 base damage. One from the M14 is 180. So, you're right, the damage per shot is higher for the LAR.
But, the M14 has double the magazine size, quadruple the fire rate, and when reloading from 0 to full on each, the M14's reload time is half that of the LAR. This is all still looking at base stats, no Sharpshooter bonus. Of course, the LAR has the advantage of interruptible reload of individual rounds, making it the better option for sustained usage against many targets, but for sheer damage output against one bulky target, the M14 takes the trophy. Also note the laser sight, allowing for accurate hipfire shots, meaning you can aim better while on the move. It takes practice to get consistent headshots at a high rate with the M14, but once you can do that, its potential is incredible.
Now, comparing the Crossbow to the M14 is a bit trickier, so let's crunch some numbers.
So, the headshot damage of an unperked Crossbow is going to be 300x4.0 = 1200, which is very nice. Offperk, that's enough to two-shot a Fleshpound on 6-man Hard. Its fire rate is much slower than the other two though, so the Crossbow is very dependent on being able to kill in 1-2 shots. On Hard and below though, the Crossbow is pretty much the Sharpshooter's bread and butter.
But what about Suicidal and Hell on Earth?
Here, the resistances of the Scrake and Fleshpound come into play.
On all difficulties the Fleshpound has mostly the same resistances, and the Scrake has none. But, on Sui/HoE, they both gain a resistance to the Crossbow: half damage for the Scrake, and x0.35 (or about a third) for the Fleshpound. So offperk the Crossbow will now do only ~400 headshot damage to the Fleshpound, which is just big enough to make him rage and too small to do more than scratch him.
A level 6 Sharpshooter has an x2.4 headshot bonus for perked weapons (x1.5 for offperk weapons), so using a Crossbow against a Scrake would result in 300x4x2.4x0.5 = 1440, enough to two-shot it on Suicidal. On Hell on Earth it'll survive the second shot with 44 health left. A third headshot from pretty much any weapon will finish the job, and on either difficulty unless I'm mistaken you should be guaranteed a stun as well, so the Sharpshooter can still make quick work of the Scrake with a Crossbow.
But against the Fleshpound? A level 6 will deal 960 damage with a Crossbow headshot, which means 3 shots on Suicidal and 4 shots on Hell on Earth, and the Fleshpound doesn't get stunned. That's just not adequate.
Now, the M14. With this, on any difficulty, the Scrake has no resistance and the Fleshpound takes x0.75 damage. A L6 Sharp will dish out 80*2.25*2.4 = 432 damage per headshot against the Scrake and all smaller zeds, and 324 damage per headshot against the Fleshpound.
On HoE, the headshots to kill comes to 7 for the Scrake and 10 for the Fleshpound. That's pretty high, but keep in mind you can empty the M14's 20-round magazine in 5 seconds flat. With the way the rifle handles it would be preposterous to get all 20 shots to be headshots firing at max rate, but with enough practice I'd say it's fair to be able to get at least half of them, or 95% of them with more paced shots.
So you could probably kill the Scrake in ~3 seconds and the Fleshpound in ~6 seconds. This makes the M14 about equal to the Crossbow against these two on Suicidal, but superior on Hell on Earth.
But on top of all that, the M14 can also mop the floor with all the smaller zeds, while the Crossbow would need a good backup weapon.
So, for Hard and below, dat Crossbow is where it's at. For Sui+, get yoself an M14. And for both of them: practice, practice, practice.
If you honestly read that whole thing, you have my thanks.
And for your future reference when comparing weapons and such, here's the thread with a download link to the PDF that has all these numbers I'm crunching.
