TheWandererI have played with both the grenade launcher and the iron bomber as well. The iron bomber essentially makes pipes easier to hit hence having have the stat of "Grenades have very little bounce and roll".
The tradeoff is that it has a slightly reduced explosion radius. -15% actually. The pipes of the grenade launcher are a bit less controlled in their arc than the iron bomber. Hence more bounce and roll. So yes you could argue that this is what makes the difference in MGE.
We're aware of the stats. We're discussing how objects are calculated changing the arc of the 2 weapons