I have already talk about it in my wishlist post in the forum, but i think it deserve a thread cause its a compatibility issue and no one have already talk about this idea.
Actually weapons have 3 attachments, scope, side and barrel.
First of all its not really realistic, its restrictive and too much arcade game like, we miss left/right possibility and more important the lower attachment for bipod, hand grip (both in one also exist) grenade launcher, rail cover and other things like this, also why not possibility to change some parts like barrel or butt, arcade game handle this and the game where the bullet realism/simulation is the more accurate don't, its disconcerting...
But anyways back to the real thread here !
Actually all of this 3 weapon attachments work in a wrong way, they need to be added in the weapon attachment compatibility list, this completely prevent a lot of compatibility, sometime from vanilla attachment on a mods/custom weapon, but more common issue custom/mods attachment on a vanilla weapon and the most common mods/custom attachment on mods/custom weapon.
We can be sure that a lot of weapon attachment and a lot of weapons itself will be create in mods, it will be a really big issue of compatibility at the end, even with the upcoming beta who will add a lot of new weapons and maybe a lot of attachments.
I have imagine a solution that can finally work in a realistic way and when its done its finally better for everyone, modding community and devs team who will not need to modified weapon file for adding attachment compatibility.
What about weapons who recognize automatically if the attachment can be mounted in based on the rail size, like real life.
I develop :
In real life we don't care about the fact that its useless to mount a sniper scope on a shotgun, it make sense by itself and if anyone in the game want to do it anyways their is no logical reason to prevent him to do so and no gameplay balance factor need some weapon to avoid them to accept some attachments.
All attachment must be set with rail length and width, both weapons and attachment have a predefined value for both, if the attachment rail length is over the weapon rail length its not compatible and can't be mounted, like its impossible to mount a sniper scope on a pistol or a revolver cause the scope is too long for this short rail, if the value is equal or less it is compatible, we can mount an holo or a red dot on a sniper if we want and its physically possible, if the width is not the same its not compatible, some weapon have a larger or a smaller rail width than the majority, pistol is the greatest example for rail width.
Every modders just have to definite both value for attachment or weapon and its done, even for devs team its still be more simple for each new weapons, rather than manually write (copy and paste) the attachment list just definite the size per rail and the attachment size.
Even if i don't like this idea : its also possible to create exclusion list that make some attachments individually or a kind of attachment (like scope or holo) incompatible with a weapon, it can prevent to use some attachment on special weapons who don't have the shape for accept it without having a collision problem or like the XM25 who have its own scope or the FAMAS FELIN.
It can also use unconventional attachment point, like the flashlight point under pistol who are for some of them unique or definite for an attachment to be only compatible with a single weapon (some attachment are interfaced or have a special things with a single weapon and can only work with a single one) again like the FAMAS or the XM25 scope for example.
In short : Weapong rail length who determine the attachment limit (sniper scope itself is longer than simple red dot), what a weapon can't accept and what an attachment can't be fit on or the only one it can be fit on.
I'm sure this idea can help a lot of people.
And i also want to say about 2 other idea about attachment :
Possibility to put more than a single thing in the same rail, for example on my airsoft sniper i have a rail cover an handgrip and a bipod, it don't look or feel overloaded, but also some scope can be mounted with another equipment like additional IR scope or the one that a lot know and who is the more popular is this : http://www.france-airsoft.fr/img-galerie/1168434438/gallery_12004_11_2168.jpg
This can be possible in a realistic way with rail length, also notice that some scope have additional rail on them : http://www.rap4.com/images/Squad_Blaster/Squad_Blaster_System_Scope_Rail.jpg
http://gungearusablog.files.wordpress.com/2012/08/ar-scope-only.jpg
Also some attachment need to have different modes, like the "holo increaser" who can be flip on the side (even if for this one the visor type switch is perfect for this feature) or activate some special feature with some attachment, it must be done from the inventory menu for keyboard keys saving feature and more easy for complex functions attachment, just possibility to open a simple menu with possibility for modders to create custom menu and even complex interface for some electronic system with a lot of possibility like ACRE radio by click on it from the inventory will be helpful for a lot of people.
I hope you can get great improvement to the game with my idea and fix the "custom/mods attachment incompatibility issue"