Let me start by saying this is NOT a recruitment thread for a game. So please do not post here saying that you want to be a part of this or asking when it is running. I may run it in the future but I will post in the games section of the site when I do.
So I had an idea for a game/campaign where the players are either members of the US Marshals or people that work for them (informants,hired muscle, ect.). They would be dealing with everything from moonshine runners to immigrant and cartel problems to high profile criminals. The time period is rife with material to work off of that could make for several interesting and fun situations.
The question comes though, what system to use? I personally want a system that is a little more combat tactical and uses a battle map and the like. That is just the kind of games I prefer instead of the more "abstract" systems such as Burning Wheel or something like that. My first instinct would be to use d20 modern but I would prefer to use something a little more lethal and preferably with some material already based on the time period. I know Cthulhu has some stuff from that time but that just seems like the wrong choice as this would be realistic not pulp. So any ideas on system to use, at the very least as a base to work off of.
Any other ideas on this would be helpful as well. Including good sources of information on the actual period, like information on guns used then, organizations that where around, that sort of thing. I know a good bit about the era already but more info can never hurt.