EPPING, N.H. — Soldier feedback, from the constructive to the blistering, has been instrumental in guiding weapons manufacturer Sig Sauer in its development of the M8 carbine, staff here said this week.

The M8, a compact alternative to Sig’s much-criticized M7 Next Generation Squad Weapon rifle, appears poised to take the M7’s place as the new standard weapon for soldiers, with significant weight reduction and key modifications that address troops’ concerns.

Among those changes is a 25-round magazine to replace the 20-round mag that shipped with the M7, said Josh Shoemaker, Sig’s product manager for defense.

The NGSW program marked a transition from the legacy M4 rifle’s 5.56mm ammo to the 6.8X51mm Common Cartridge, an internally designed caliber used both by the rifle and the coming M250 light machine gun. For some soldiers accustomed to the M4’s 30-round magazines, this has represented a major concern.

“Guys are coming from the 5.56mm system, where they’re used to being able to carry seven 30-round magazines into combat, so they have 210 rounds, roughly, going into a fight,” Shoemaker said in an interview. “Well, now that they’ve gone to this larger caliber, there’s 20-round magazines, so you’re reducing the volume of rounds that you have.”Previously, Sig Sauer and the Army have emphasized that the 6.8mm round is heavier and carries greater kinetic energy and power, allowing troops to use fewer rounds to achieve the same effect on a target.

Last year, Brig. Gen. Phil Kinniery, commandant for the Army’s Infantry School and Maneuver Center of Excellence at Fort Benning, Georgia, told Task and Purpose that the 6.8mm ammo “stops the enemy at one round” versus the several rounds the legacy system would require.

Regardless, Shoemaker said, that purported difference can’t be seen in training; paper targets respond the same to bullets of either caliber.

Early criticism has cited ammo-management challenges in training with troops who find themselves with only 140 rounds to fire instead of the 210 they’re used to.

“Guys are having to think, ‘OK, well, how much ammo do I have left?’”Shoemaker said. “Sig has already, in a year’s time, developed a 25-round mag solution to extend some of that mag capacity out of the gate.”It’s not clear if that 25-round magazine will immediately ship with the M8 carbine when fielding of that weapon begins in December.

Shoemaker said the alternative magazines were in early soldier evaluations and feedback and had to complete a full Army evaluation before they could be approved for use by soldiers.

“But in terms of production and manufacturing, we’re pretty much ready to go here in the next few months, to start spitting those out,” he said.

Soldier feedback also pushed Sig Sauer to design a more rigid handguard on the M8, eliminating some of the flexibility in the M7 that had presented a problem for soldiers.

“We saw that with the guys jumping out of planes, and they were like, ‘Hey, man, we’re getting a lot of flex, and then our lasers don’t line up, and we can’t hit targets at night,’” Shoemaker said. “That’s a real problem.”The new handguard uses a newly developed insert and additional screws to reduce unwanted movement to a minimum. It will come standard on the M8.

“The M4 was in service for over 60 years, and it had a lot of iterations in between that,” Shoemaker said. “There will be continuous improvements and evolutions of that as we go along. … And as the system matures, some of that feedback gets more and more nitpicky, you know, and we love it. The smaller stuff is just as important to us as the big stuff.”