If 4d hits 50% of the time, is it ≈ 8d-24?

[Raekai]

It's hard for me to explain what I'm looking for in a short title (and I'm admittedly not totally sober).

I ask because I like the combat approach of Into the Odd (another tabletop RPG), which makes all attacks hit, which takes boring misses out of combat. However, taking defenses out also means that there's not a way to avoid damage entirely. I want every attack to hit, but I don't want every attack to do damage.

So, is there a way to do something like that in GURPS (even if it would be too much trouble)? If every attack hits, it seems like you would modify damage based on the chance that the attack would hit (in addition to DR and such). Which is where I got 50% chance of 4d ≈ 8d-24.

It seems like there'd have to be an easy way to calculate the odds of an attacking doing damage based on skill and active defense (and I doubt there is other than a hard formula or a large table). Otherwise, I haven't figured out to how to calculate 4d hitting 25% of the time, 75% of the time, and so on. It doesn't seem like this would be very granular either. You could map it to the steps of the 3d success roll, but it seems like partial dice would have to be used, which wouldn't work.

Thanks!