|The Barrett XM109|
If you're thinking it looks like an M107A1, you'd be right. The XM109 is essentially a different upper-receiver using the same lower-receiver as the M107A1. You might also be thinking what those rounds are. Those my friend are most certainly not 12.7x99mm (.50 BMG) rounds, those are 25x59mm rounds. A bad day for anyone unlucky enough to catch one of these in the anywhere.
So what's the deal? It's a bigger bullet, way more kinetic energy, but they shortened the barrel? Well it still out-ranges the M107A1 and deals out more power. Reportedly being able to punch through light armor (perhaps a BTR-70) and materiel at 2,000 meters (i.e. 1.2 miles). It has a shorter barrel, higher effective range, and it shoots what might as well be considered (and are in fact considered) grenades, and not the 25x40mm mess the XM25 shoots (that was considered "no lethal enough" by many).
So to the stats, we'll compare the M107A1 to the XM109.
XM107A1: 55/110/220; 2d10+3; ROF1; 10 shots; 27.5 lbs; AP4, HW at half damage
XM109: 65/130/260; 4d8; ROF1; 5 shots; 33.2 lbs; Ballistic Computer, HW, SBT
And things vary with the ammunition types... well lets compare some common ammunition types too:
Raufoss Mk 211 Mod 0 (AP-HE-I): 1d6 damage; +6 AP. This makes the damage 2d10+d6+3 at AP10. That's pretty darn good, and its pretty much the standard US used round with the M107A1.
AP: +1d8 damage; +6 AP (On contact only),
HE-AB: MBT over target (airburst)
HEDP: +3 AP (contact only), MBT
So for a direct shot, HE-AP would be the best for that single shot making it 5d8; AP12, HW. Also really good by overkill on a single man. Theoretically at least.