Leave it to the Army to create something where a need doesn't exist! This is a perfect example of lobbying run amok.
The .277 Fury (6.8 x 51mm), which the XM7 fires, is essentially a .308 case firing a .27 caliber bullet. Ballistics wise, it doesn't have a lot of benefit out to about 500m. Most people can't shoot that far anyway. In fact, very few can shoot that far with any accuracy. And, that's under normal conditions. In a high stress battle scenario, under direct fire, most accuracy beyond 100m is unreliable in real world situations. Doesn't matter what you can do at the range; on the battlefield is where the rubber meets the road.
Out past 500m the .277 Fury has a little flatter trajectory with slightly higher velocity. Energy differences are negligible between the .277 and .308. If anything, the .308 actually has the advantage here, with slightly less velocity and maybe 1" more drop. You've got to get out to 700m-750m before the .277 starts to show any measurable differences ballistics wise. Even then we're talking about a delta of about 8". One troop out of a thousand "might" be able to shoot that far with any degree of accuracy. (just being realistic here).
So, the Army has endorsed a round which is a non-standard round in a world where the .308 has long existed and performs nearly identically to the .277 for all practical purposes. And, they've put it into a rifle which is fully 3.5lbs heavier. That's a LOT! I'm even being generous here too, using nominal weight of 9 lbs for the XM7 versus 6 lbs for the M16 or 7.5 lbs for the FN SCAR (now being issued to some SOCOM troops). The more likely weight for the XM7 is on the order of 10.5 lbs fully fitted with a suppressor and a full magazine.
The terminal ballistics for the .277, .308, and even the 5.56 are nearly identical out to 300m-350m, with the 5.56 having much less energy simply due to the reduced mass (obviously).
Bottom line...This adoption of the XM7 and .277 Fury, if it really does happen, makes exactly zero sense. If anything, it's a step backwards for the troops in the field. (but some general will get a swimming pool out of the deal, that's for sure. Probably a whole lot more than that!).
The .277 Fury (6.8 x 51mm), which the XM7 fires, is essentially a .308 case firing a .27 caliber bullet. Ballistics wise, it doesn't have a lot of benefit out to about 500m. Most people can't shoot that far anyway. In fact, very few can shoot that far with any accuracy. And, that's under normal conditions. In a high stress battle scenario, under direct fire, most accuracy beyond 100m is unreliable in real world situations. Doesn't matter what you can do at the range; on the battlefield is where the rubber meets the road.
Out past 500m the .277 Fury has a little flatter trajectory with slightly higher velocity. Energy differences are negligible between the .277 and .308. If anything, the .308 actually has the advantage here, with slightly less velocity and maybe 1" more drop. You've got to get out to 700m-750m before the .277 starts to show any measurable differences ballistics wise. Even then we're talking about a delta of about 8". One troop out of a thousand "might" be able to shoot that far with any degree of accuracy. (just being realistic here).
So, the Army has endorsed a round which is a non-standard round in a world where the .308 has long existed and performs nearly identically to the .277 for all practical purposes. And, they've put it into a rifle which is fully 3.5lbs heavier. That's a LOT! I'm even being generous here too, using nominal weight of 9 lbs for the XM7 versus 6 lbs for the M16 or 7.5 lbs for the FN SCAR (now being issued to some SOCOM troops). The more likely weight for the XM7 is on the order of 10.5 lbs fully fitted with a suppressor and a full magazine.
The terminal ballistics for the .277, .308, and even the 5.56 are nearly identical out to 300m-350m, with the 5.56 having much less energy simply due to the reduced mass (obviously).
Bottom line...This adoption of the XM7 and .277 Fury, if it really does happen, makes exactly zero sense. If anything, it's a step backwards for the troops in the field. (but some general will get a swimming pool out of the deal, that's for sure. Probably a whole lot more than that!).