On Rolling Dice

I’m implementing skill checks in BFD right now and got to wondering about dice probabilities. One of the things I wanted to try and avoid is using pure probability values in the belief that by using a dice based system people will have an easier time visualising what’s going on behind the scenes and can discuss it better. I also want to attract fans of tabletop gaming.

I have experience mostly with DnD and Games Workshops games and to be honest I always felt that both of them are lacking in opposite areas.

DnD (4e specifically) is as you hopefully know a D20 based game where your normal skill check is to roll a D20, add your modifiers to it and see if you beat the  target skill. This results in some very large numbers being thrown around which can get a little confusing and having double the skill not always meaning you’re twice as likely to succeed.

GW games on the other hand prefer stats that only tend to range between 0 and 10 with 3’s being considered “average”. Most skill checks with their systems depend on looking up the two stats involved and finding a target value for a D6 roll. Normally if the two stats are equal then this would be a 4+ (50%) if your is 1 more than your opponents it’s a 3+ (66%) and if it’s more than double it’s a 2+ (83%).

I like the small stats of GW games but not the probability distribution. If I have double the weapon skill of my opponent I should be twice as likely to hit them (75%)  and if I have triple their skill I should be twice as likely again (88%).

These values only come up when dealing with re-rolls though. A 4+ on one D6 with a Re-roll is a 75% chance of success (and with 2 re-rolls it’s 88%). So I could say that having double the skill of the target lets you reroll a failure and triple lets you reroll two failures. This sounds great but it makes having a slight 1 or 2 point advantage useless.

So I ask the tabletop playing public who have no doubt done the maths on this already: Is there a dice system that would give me the distribution I crave with the granularity needed?