Weapon accuracy (range, damage, spread, recoil and so on) should be left to the game designer to be able to set in the weapons editor properties dialogue box preferably (accuracy/range) and or at least in the weapons setup up file in the relative folders.
The default accuracy can therefore be set at anything one would like but 100% accuracy should be possible to be set.
As to the realism : trajectory, velocity, falloff and alike well that's another issue and not necessarily of the same significance to all game makers and game players for reasons you should be able to work out for yourself and is or more accurately speaking as has been alluded to potentially a minefield. The number of things in real life that can affect the accuracy of a weapon or other projectile can be many and varied in each circumstance.
If you go down that road then you should go all the way which is in my opinion beyond what Reloaded or any other game engine or other product should seek to do unless it is specifically is designed as a software to relate specifically to weapons design in ware fare use or other which is not in the main what game players are interested in though some may well be very interested in that aspect. Most game Players want fun and enjoyment and that whats Reloaded should return. In the main in the first instance as some have said a game player would normally expect to hit an object at the point of cross hair. Deviation from that is OK within reason but extremes of making a Game weapon widely inaccurate or difficult to use should be avoided by default. Let the Game designer make it more difficult if they so wish and not the other way around.
End user game player "Game Difficulty" settings may at some point be worth considering later where perhaps all things e.g. Characters, weapons and other challenges could be either chosen as a difficulty level by your game players or games designed with increasing difficulty either in a linear fashion or level by level fashion.
Getting back to the weapon realism thing this is game making and not necessarily is there any need to enforce anything hard coded as being accurate to real life. In any case achieving what is real for any individual game player as if they were using a weapon in real life is impossible as each individual would have differing capabilities, results, expectations and real time scenarios when firing any weapon at any target, static or moving which poses additional issues.
As said to go down that road if you want real then you have to have real and that means more permutations than you can ever account for............
It means accounting for human walking, running, breathing, position and stance, kneeling, laying down, balance (depending upon what you are standing upon and how stable the player is or would be in real life) as well as weather, heat, cold, time of day, shooting through grass, tree branches, twigs, water, ice, glass, wood (e.g. you can shoot through wood in real life and still hit something if on target - generally speaking we cant shoot through boxes or a fence or even metal objects, fabrics and so on and kill an enemy or vice versa in game engines - but you may well be able to do so in real life, wind, rain, snow, hailstones, flies, birds,(anything that the projectile may hit in the slightest that may impact on its angle/flight path and the further the projectile travels means a hit becomes a miss) distance/range to target estimation, vertical trajectory (shooting up/shooting down) and more.
True to say the more you do something the better sometimes, for some people they can become at it though not in for others in many instances in reality. Some find some things easier than others. Shooting a weapon in real life can be like driving a car - the more you do it the more it becomes second nature and all shooter calculations and things that have to be taken into account that one may find very difficult at first can become easier and with continual practice and effort and a lot of time, practical application and experience it becomes as said something that becomes a natural extension of oneself and the thought and physical processes become automatic and natural.
Unlike real life many game players don't have that much time available to master something. They may play your game once to the end if you are lucky and often cant wait to get to the end and complete it as fast as possible for some strange reason. If they don't like it for any reason, find it too hard or boring and repetitive or not enjoy playing it they may not even do that and give up at any stage. If they play it once they may not ever want to play it again even if they enjoy it.
Point being every game player is different, some like one thing, to another it will be a complete turn off and killer for your game. Thus think of what the majority enjoy and that's killing and not getting killed too often in return.
Most people don't mind something that's an interesting and enjoyable challenge as long as its not permanently difficult and or repetitive. By and large they like to win and achieve and be rewarded more often than fail and lose. Quite naturally.
In an fps shooter if you are going to make using weapons a bind for end users then you take the enjoyment away completely as it is their link to the game world.
Whatever game maker and game player flexibility of choice is the key. The more the better so the games made can be as hard or easy as needed, required, suitable for all depending upon the game design needs.
If you want close proximity to absolute reality then we should extrapolate that to everything else in the game world for every type of game scenario for every game player expectation. e.g. vehicles, flying objects and so on - all static and dynamic world objects which is fine.....but we may have to wait around 20 years at least to get it done unless we can get a big investment in additional development resources, money, man power and alike.
Some game Character reality would be nice. Real looking, moving, talking, eyes, facial movements and expressions and extensive real like behaviors and alike.
Liquids, realistic surfaces, ice, oil, realistic moving fabrics, leaves, plant seeds, dust, and sandstorms (Lees favorite) and so on and the list goes on and is endless.
Yes we want as much as possible and as realistic as possible but we also want a fully working game making product at an acceptable level as soon as possible by and large for the benefit of the product and all concerned. As with all things some compromise, reason and sensibility may be needed and quite likely to be so by force of necessity and reality of the development and product capability itself not to mention any commercial realities.
The real aim and skill of making a successful game is not necessarily how good it is realistically but how enjoyable it is for the end game players and that in the end is perhaps more difficult than anything else to get right.
Lees post above about improvements to weapons seems to me to be quite adequate enough for the time being.
