[Icelander]

So, has anyone statted out the 45 Raptor round?

While it will not work form an AR-15 type rifle, which is certainly a complication, the ability to fit 20-rd in a standard AR-10 type magazine is a huge increase in firepower compared to .450 Bushmaster, .458 SOCOM or .50 Beowulf.

Sure, using the AR-10 as the basis means that the weapon will be larger than a carbine made from AR-15 components, but the US legal barrel length limit of 16" means that all the AR-15 carbines will have Bulk -5 anyway, meaning that the size difference is abstracted away in game terms. Only if the characters have the means to either wait for the paperwork to register their firearms as SBRs or the inclination to ignore the legalities can they take advantage of the reduced profile of the AR-15 compared to AR-10, chambering a 10"-14.5" barrel AR-15 in one of the monster hunting calibers.

I believe that the in the real world, big bore semi-automatic rifles and carbines may be a solution looking for a problem, but in a world with supernaturally tough critters, the ability to rapid-fire 240-400 grain expanding projectiles at rifle velocities suddenly becomes very valuable. Sure, .308 well placed will do for nearly any realistic hunting, but against regenerating werewolves or nigh-indestructible vampires, tulpas or shoggoths, sometimes you need a weapon shooting at .308 velocity with a bullet that is at least 150% the mass of a .308 and expands to 0.6-1.0 inch diameter.