The Chain Reaction 2.0 rules are now being offered as a free .pdf download by Two Hour Wargames! These are the basic rules upon which the majority of Two Hour Wargames other sets like Nuts! and FNG are based.
The rules cover all the reaction test mechanics and provide stats for a variety of weaponry, so they make a great set for any modern skirmish.
If you haven't tried the Two Hour Wargames style rules I'd give them a go (you can't complain about the price!). They do have a learning curve but once you're over that they are excellent.