Analysis of information sources in references of the Wikipedia article "XM7" in Portuguese language version.
The intermediate caliber 6.8mm cartridge falls between the 5.56mm, which is in the M4 and the M249 Squad Automatic Weapon, and the 7.62mm round in the M240 machine gun.
[SIG] runs 20 and 25-round [6.8] Lancers in [the SPEAR] currently, but... any 7.62 [NATO] magazine interfaces with it.
The intermediate caliber 6.8mm cartridge falls between the 5.56mm, which is in the M4 and the M249 Squad Automatic Weapon, and the 7.62mm round in the M240 machine gun.
[SIG] runs 20 and 25-round [6.8] Lancers in [the SPEAR] currently, but... any 7.62 [NATO] magazine interfaces with it.