not everyone carries the SAW
but ammo for it is divided up in the squad
with the XM25 I gather there will be a grenadier in the squad
why not have him thumping a 40mm smart and dumb rounds?
That way he can be resupplied from the 40mm cannons?
XM25 is pretty hefty already - what would a 40mm version weigh? Isn't the Mk19 auto-grenade launcher a 300-pound setup? (looks up weight) Ah, much lighter than I'd thought - "only" 72.5 pounds for just the gun, plus the weight of a case of linked 40mm grenades - another page on the Mk19 lists weight for the gun, tripod, and traverse-and-elevation mechanism at 120 pounds, plus 64 pounds for a container of 48 rounds. There was a link to the Mk47 Striker 40mm auto grenade launcher, as well, which at 55 pounds (gun only) is lighter than the Mk19 and can fire "smart" 40mm rounds similar to the XM25's 25mm rounds. Hmmm. It's still pretty hefty, though - the XM25 is MUCH lighter even than the Striker, which is still listed as needing a tripod (and presumably T&E).
I'm presuming that you weren't referring to regular 40mm grenades, as used in the M203 and that 40mm-grenade revolver job - the XM25 would have far greater range, AFAIK.