This post from Isegoria that got me thinking about this. The heavy grenade launcher could fire a full size 40 mm grenade out to 1500 meters using the same ammo as automatic grenade launchers. This has more recoil than the M32 which would be handled the same way an anti material rifle does – fire from a bipod and have a heavy muzzle brake.
I figure that since an automatic GL and a heavy machine gun both fire from a tripod and weigh about the same that a single shot HGL would require similar measures to an anti-materiel rifle. This gives the platoon long range firepower where its current grenade launchers can’t shoot further than its assualt rifles.
In the anti material role, it would use shaped charge ammuntion to give it a armor penetration superior to the 50 cal in most cases.
The heavy grenade launcher would have a similar weight to an anti material rifle (approx 30 pounds). This is because its high-low pressure system allows it to have a thinner barrel. Its ammunition would weigh about twice as much as a 50 cal cartridge. In 25 mm with fire control to compensate for blast, the weight would be correspondingly less.