I use a different system...one that I brought over from my 1st and 2nd edition days. I use a D6/D10 system. The D10 is rolled to generate a number between 1-10, of course, but the D6 is used to determine whether the D10 is either 1-10 or 11-20. It goes like this ........
D6/D10
1/1 = 1
1/2 = 2
1/3 = 3
1/4 = 4
1/5 = 5
1/6 = 6
1/7 = 7
1/8 = 8
1/9 = 9
1/0 = 10
the same is so for the 2 and the 3 on the D6. As for 4,5 and 6 on the D6 it moves to the high range:
4/1 = 11
4/2 = 12
4/3 = 13
4/4 = 14
4/5 = 15
4/6 = 16
4/7 = 17
4/8 = 18
4/9 = 19
4/0 = 20
5 and 6 also create a number between 11 and 20.
Here is where I customize it.
Special Rolls:
1/1 = miss / critical failure (D4 rounds of inaction - nasty)
2/1 = miss / critical failure (1 round of inaction)
3/1 = miss
I only make my players suffer bad form, where they have to spend time to recover from a critical failure.
4/0 = automatic hit / normal critical chance
5/0 = automatic hit / automatic critical
6/0 = automatic hit / automatic critical + 1 additional damage dice for this hit (per the weapon type) + Initiative for the next round (we roll initiative every round, not every encounter)
If I have the formula correct there are a total of 60 possible combinations using this system. Which breaks down to a 5% chance to generate any single number between 1 and 20, three combinations for each (same as the D20 system), but to roll any one of the special rolls listed above there is only 1 combination and that equates to a 1.67% chance.
Just wanted to share...I am sure some of you have used this D6/D10 system before, but this is my slant on it.