[Science] The Hard Science of Low Gravity versus High Gravity

[Huscurian]

I have a question, a scientific one, that may play into GURPS.

I have a setting that I've formulated in my mind. I also have gotten started on characters for my two players, who will be playing together. However, the setting is high-tech with some ultra-techy stuff thrown in.

The real question becomes, how do you account for the mass, the propulsion/acceleration/thrust, and/or the trajectory or speed of a projectile on low or high gravity worlds?

The setting does include strong, muscular men, but most of them are genetically engineered. Humans, the minority of the world, are strong like them but not as strong as they are.

This is one of those things that I'm trying to decide. On low gravity worlds, people are much more likely to be leaner, elongated, and have lighter mass, having far difficulty in working out and gaining muscles. On high gravity worlds, it's possible with the density of the gravity, the person could have larger muscles, and endure the tougher conditions of the world.

Let me give an example.

Let's say that a BDRM equipped with a railgun, a recoil-less burst-mass driver, is driving along the desert plains. Alongside the BDRM is a IS-3, a heavily modified tank carrying a laser cannon, self-propelled torpedo tubes, and anti-personnel guided flechette missiles. They're driving at the maximum speed of 40 MPH. They approach infantry within their range. The IS-3 fires off its anti-personnel flechette missiles (small, compact ones) with the BDRM firing its burst-mass driver (small round bolts like Battlestar Galactica) at the same time to eliminate this new obstacle.

How do you account for the factors in low or high gravity, given on account that the BDRM is less heavier than the IS-3?

I hope this thread provides some interesting answers.