Yeah, I do mean the foregrip, but it's kind of hard to be sure that is what we can see. However, it looks to me like we are looking at the top edge of an AR-15 leaning on the packs behind the guys, it appears to have the six vent holes on it facing us, visible in between the front and rear of the foregrip, which appear to have had bands of green tape wrapped around.
In other words, I think we can see this part of an AR-15 (and this one in my photo definitely is a Vietnam War era military issued AR15, since it has a 'Property of US Govt M16A1' stamp on its receiver, but above that it also has 'Colt AR-15' in big letters to the right of the prancing horse Colt logo):
Sorry about the slight derail, but it's probably an XM177 in the original picture. Issued 1966-7 so the timescales fit. Looks like a 30-round mag in the '16 too, which is unusual.
The gun geek in me WILL break out every now and again