The procurement price of the XM7 is unaffordable even if the performance of the weapon and ammo are exactly as claimed. The price of the rifle is $4,400 and the FCS is $11,300 for a total of $15,700 per soldier.
Suppose that for comparison we use the M27 (made by H&L based on the short stroke piston 416) rather than the M4A1 as an example since the Marine Corps has already equipped all of its infantry with M27s and the M4A1s are only for support units. The contract price of the M27 when the last IDIQ was awarded was $1300 per rifle. A Trijicon VCOG is ~$2500. An M27 with a VCOG is still only $3800 or less than 25% of what the Army proposes to spend on the XM7 weapon.
Since the invention of gunpowder, 95% of infantry rifle engagements have taken place at distances of less than 300m. If hitting targets beyond 500m is the use case for the XM7 and 6.8x51mm cartridge then it is optimizing for engagements at ranges that are primarily the domain of snipers with special rifles and comprise probably less than 2% of infantry combat.
The weight of equipment that the average infantryman can carry is finite and no amount of money will change that. Ounces==pounds==pain. The weight of the XM7 and ammo is significantly more than the M27. A 33% reduction in the number of rounds that a soldier can carry arithmetically requires that the consistent accuracy of the shooter must increase by 50% to have the same lethality. The anecdotal evidence doesn't indicate that the XM7 and the FCS have produced a magical 50% increase in accuracy. If they carry more than seven magazines, they will have to not carry some other piece of equipment because a soldier's load directly impacts his speed, range, and endurance.
The properties of steel alloys are not going to change significantly. Most AR barrels are made of 4140 steel with proprietary heat treatments and quenching and chrome lining in the bores. Sig Sauer has never advertised that the MCX Spear or the XM7 have any revolutionary metallurgy in the design. If that assumption is correct, the service life of the barrel and the bolt of the XM7 is going to be far less than the 5.56mm NATO or 7.62mm NATO weapons. The relationship between chamber pressure and barrel fatigue and erosion is not linear. The increase from 62,366psi for a 5.56mm NATO chamber to the 77,000psi for the 6.8x51mm XM7 cartridge is not going to produce a corresponding 23% decrease in barrel life. It's probably going to be closer to a 40% reduction in barrel life.
Short barrel life matters a lot because the Army will end up having to provision for 60% more rifle barrels and bolts and those will have to be available at the forward support units and not at maintenance depots.
As mentioned in the article linked above, the 6.8x51mm cartridge has a surface danger zone that is closer to a .50 BMG than to a 7.62mm or 5.56mm round. The SDZ for .50 BMG is 7200m and for 7.62mm and 5.56mm the SDZ is 3600m. Oddly, the SDZ for the 6.8x51mm cartridge has not been released to the public. It's probably because the Army has 659 centrally funded small arms ranges and only about 10% of those can accommodate .50 BMG. In other words, the Army would be at a 90% deficit of the number of training ranges needed to train soldiers equipped with the XM7 service ammunition. They are not going to make that admission to Congress.
The Army simply doesn't have the budget to buy additional land or modify existing ranges to accommodate the XM7 combat ammunition. So, PEO Soldier has already decided that there will be a 6.8x51mm reduced charge training cartridge that will be used until units are deployed to combat, at which time they will get the combat ammunition. This acknowledges that the RCTM cartridge will have different ballistics than the combat ammunition and the weapons will have to be zeroed again when soldiers deploy for operational missions. It is really surprising that they are accepting that soldiers will train with different ammunition from that with which they will fight.
None of this makes sense to me. There just isn't that much improvement in lethality to be had with a "better rifle." The current M4A1 has mechanical precision that exceeds the skill of nine out of ten military shooters, if not 19 out of 20.
Suppose that for comparison we use the M27 (made by H&L based on the short stroke piston 416) rather than the M4A1 as an example since the Marine Corps has already equipped all of its infantry with M27s and the M4A1s are only for support units. The contract price of the M27 when the last IDIQ was awarded was $1300 per rifle. A Trijicon VCOG is ~$2500. An M27 with a VCOG is still only $3800 or less than 25% of what the Army proposes to spend on the XM7 weapon.
Since the invention of gunpowder, 95% of infantry rifle engagements have taken place at distances of less than 300m. If hitting targets beyond 500m is the use case for the XM7 and 6.8x51mm cartridge then it is optimizing for engagements at ranges that are primarily the domain of snipers with special rifles and comprise probably less than 2% of infantry combat.
The weight of equipment that the average infantryman can carry is finite and no amount of money will change that. Ounces==pounds==pain. The weight of the XM7 and ammo is significantly more than the M27. A 33% reduction in the number of rounds that a soldier can carry arithmetically requires that the consistent accuracy of the shooter must increase by 50% to have the same lethality. The anecdotal evidence doesn't indicate that the XM7 and the FCS have produced a magical 50% increase in accuracy. If they carry more than seven magazines, they will have to not carry some other piece of equipment because a soldier's load directly impacts his speed, range, and endurance.
The properties of steel alloys are not going to change significantly. Most AR barrels are made of 4140 steel with proprietary heat treatments and quenching and chrome lining in the bores. Sig Sauer has never advertised that the MCX Spear or the XM7 have any revolutionary metallurgy in the design. If that assumption is correct, the service life of the barrel and the bolt of the XM7 is going to be far less than the 5.56mm NATO or 7.62mm NATO weapons. The relationship between chamber pressure and barrel fatigue and erosion is not linear. The increase from 62,366psi for a 5.56mm NATO chamber to the 77,000psi for the 6.8x51mm XM7 cartridge is not going to produce a corresponding 23% decrease in barrel life. It's probably going to be closer to a 40% reduction in barrel life.
Short barrel life matters a lot because the Army will end up having to provision for 60% more rifle barrels and bolts and those will have to be available at the forward support units and not at maintenance depots.
As mentioned in the article linked above, the 6.8x51mm cartridge has a surface danger zone that is closer to a .50 BMG than to a 7.62mm or 5.56mm round. The SDZ for .50 BMG is 7200m and for 7.62mm and 5.56mm the SDZ is 3600m. Oddly, the SDZ for the 6.8x51mm cartridge has not been released to the public. It's probably because the Army has 659 centrally funded small arms ranges and only about 10% of those can accommodate .50 BMG. In other words, the Army would be at a 90% deficit of the number of training ranges needed to train soldiers equipped with the XM7 service ammunition. They are not going to make that admission to Congress.
The Army simply doesn't have the budget to buy additional land or modify existing ranges to accommodate the XM7 combat ammunition. So, PEO Soldier has already decided that there will be a 6.8x51mm reduced charge training cartridge that will be used until units are deployed to combat, at which time they will get the combat ammunition. This acknowledges that the RCTM cartridge will have different ballistics than the combat ammunition and the weapons will have to be zeroed again when soldiers deploy for operational missions. It is really surprising that they are accepting that soldiers will train with different ammunition from that with which they will fight.
None of this makes sense to me. There just isn't that much improvement in lethality to be had with a "better rifle." The current M4A1 has mechanical precision that exceeds the skill of nine out of ten military shooters, if not 19 out of 20.
