Utterly Mad

I've decided to keep the 7.62x24mm round and cut its range down to 550m, this is a weapon designed to be used on ships, it's intentionally supposed to hit something and stop or bounce off a hard surface to prevent damage to the ship interior.

Well, like I said, using the next closest RL analogue as a basis, you'd have something like 45 ft-lbs of energy at that distance. Which is not enough to do much beyond give a good bruise. At 100 yards, you still have just enough power to probably kill someone (around 300 ft-lbs). It's just not heavy or fast enough to carry out well

Having been hit with ricochets from the cartridge I reference while shooting targets roughly 25 feet away, I can tell you it probably won't even break skin. I'd really just make it bigger, personally. Put the equivalent of space .308 in there, maybe. Or maybe use the existing cartridge and call it an SMG (which is what something like that would be IRL), knock the range down to 200-300 yards, and build up a GPMG to go with it.

Like I say, just my 2 cents. I'll leave final say as to how effective it is to you and the other GMs, being that it's a game and all.