maybe you can get that someday with quantum physics. We got Plasma weapons, right?
You don't need to wait for it hombre, and you don't need quantum physics. Blended metal tech is already here. The only reason the US military doesn't use it, I believe, is the same reason they don't use hollowpoint ammunition- it's considered inhumane to do that much tissue damage to an enemy. Don't believe me? Check out this video. Goes right through and armor plate, but the results from hitting a porkchop could almost be described as explosive. Also is designed not to go through drywall, so if you use it in say, a self defense situation in your apartment your neighbor's head doesn't end up like that pork chop if you miss. Your assailant on the other hand...
http://www.youtube.com/watch?v=poV4xM9Nxps&feature=related
I would rather see the bullet characteristics determine the damage like in real life, rather than what type of weapon you shoot them from. An M4, AK-74, what-ever, all basically 5.5~mm rifles are all gonna cause about the same damage to a target as a .G3, AKM, FAL 308/7.62 whatever. Terminal balistics tests show similar soft tissue damage at normal engagement ranges for all these guns/rounds (those SS109 5.56mm rounds really are nasty little buggers). So our in game 5.56mm chinese assault rifle, an AK-74 like weapon (really 5.45mm) and the 5.56mm assault rifle, a G3 like weapon (really 7.62mm) should have about the same terminal effect as the .308 sniper ( a real world sniper round, the 7.62 NATO). The difference should be in the accuracy, not the damage. I've hit stuff well over 700m with the .308 and the 5.56 starts to crap out at 500m.
No, no no. I'm sorry, but you're completely wrong. First, observe this completely fact based chart I have uploaded for you.
http://img175.imageshack.us/img175/6149/assaultrifleroundwounds.jpg
Each caliber has different levels of penetration, frangibility, and force imparted on the target all play a role in how much "dead-er" each shot makes your target. Admittedly, all of those take a backseat to shot placement, but this stuff is still important. So each caliber behaves differently, not the same. Sure, they all kill things, but to say this makes them alike is oversimplifying it. Not only that, but take the same caliber of ammunition, and fire it out of two guns with different sized barrels, or barrels with a different rifling twist ratio, and you'll be looking at two very different ballistic profiles. In fact, the US military has had issues with the M4 carbine, in that the terminal ballistics at engagement range for the M4's shorter barrel are inferior. As a result the military had a new 5.56mm load developed that had optimum terminal ballistics for carbine length barrels. It is in use by special forces as we speak and you can see it on the chart as the Mk.262. I won't go into depth about the pros and cons of each and every round, but you get the idea from the chart that tissue damage is NOT going to be the same.
What I think would complement this would be, like you said, different ammo types. You can assume most military surplus stuff is ball. So you could have FMJ with accuracy modifiers, AP with DR modifiers. For handgun rounds you could go with any of the types of fragmenting rounds for more dam. and APs for DR mods.
I most certainly agree, for variety's sake. But please, don't tell me that all the guns should behave the same in combat, even if it was true in real life, this is an RPG, and RPGs NEED for different weapons to have different stats; it's part of what makes upgrading to a new gun fun. If every gun was the same it would be a matter of aesthetics only, which seems boring to me.