I did some testing of my own in the virtual arsenal and came to the same conclusion. It's zeroed at 100m, although it will travel a bit further if you are standing up. In most other games with GL's that can't be zeroed, I get used to adjusting my point of aim. The thing that throws me off in Prairie Fire is that I actually have to aim downwards to hit with most of my shots, which are close range shots in the jungle. I'm so used to the way GL's usually fire a round straight forward and rely on you to aim upwards to compensate for the drop. The way I've been dealing with it is by looking at the angle of the barrel in my hands and adjusting my aim until the muzzle is pointing slightly above the target.
I'd prefer it if the zeroing of the sawn-off M79 was 75m, 50m, or ideally, adjustable. But at least there is one good thing about the high zeroing, which is that it increases the effectiveness of the buckshot rounds. Prairie Fire seems to treat all buckshot weapons as firing a hollow cone of projectiles. The spread of the GL buckshot is so high that it's entirely possible to have half of the pellets hit the ground in front of you, while the other half flies over your targets. The steep pitch of the sawn-off M79 ensures that the lower half of your pellet cone will fly straight ahead. So it's easier to hit targets with buckshot from the sawn-off m79 than the full length version.
