Some of the early wargames did not have a “to-hit” roll as we know it. Rather, the attacking unit would roll a number of dice based on the number of figures eligible to fight in the unit. Don Featherstone and Tony Bath usually rolled 1 six sided die per 5 or 6 figures for example. This was fairly common in their rules. The resulting total was the number of hits caused. The defender (the unit being attacked) was awarded a “saving throw” based on armor and situation. The player got a die roll for each hit. If the die comes up the saving throw number or better, that hit is negated. Pretty simple.
Rolling a die per 5 figures can make combat bloody. Consider, the average roll on 1 die is 3.5. So with 10 figures, you would get an average of 7 figures or a 70% hit rate. Most figures will get a saving throw of a 5 or better on a single die. So 1/3 of those hits will be negated. That means that one attack of 10 figures will cause 4 or 5 casualties. If the defending unit is only 10 figures, that means they’ve taken nearly 50% casualties in a single round. Apparently Tony Bath thought the same thing. In his later incarnations of his Ancient rules, he started dividing the total hits by 2 before applying. In Don Featherstones Ancient rules found in his book “Lost Tales”, he made a die roll per 10 “points” which resulted in 3.5 hits or about a 35% hit rate instead. The statistically minded will note at this point that 35% is very close to the chance of rolling a 5 or a 6 on a single die (33 1/3%).
Rolling a die per a set number of figures can be messy. What do you do if the number of figures does not divide evenly? They had some not so elegant mechanisms for figuring this out with 3 or 4 figures leftover getting to roll a die on 1 or 2 figures leftover not. It seems to me that rolling a die per eligible figure and scoring a hit on a 5 or a 6 would be most optimal. You don’t have any of the problems of rolling for total hits. What you are doing is getting the hit rates that some of the early writers were going for. The saving rolls will reduce this hit rate even more. The only problem you have is that sometimes you will have to roll lots of dice at once. Some will find rolling handfuls of dice a turn-off while others will find it just plain fun!