Just to clarify, I won’t be talking in great detail about handguards or foregrips in this post, just grips for the firing hand.
Stocks
Stock attachments were already implemented in the last view we had of the 4.X attachment menu. I’m just going to say somethings about how stocks might affect the weapon that they’re attached to and how they might affect other attachments.
A good, solid, well installed stock will increase accuracy, especially while ADSing, but a low tier stock, a folding stock, or a stock that has been damaged by poor installation, extensive firing, or use as a melee weapon will be detrimental to accuracy.
An inline stock offers benefits to recoil management, but requires the use of elevated sights.
A dropdown stock allows the use of low sights and, when used with elevated sights, allows a decent sight picture even while wearing obtrusive headwear such as gas masks or faceplates.
A hinged butt plate would increase the time it takes to deploy a bipod or shooting sling, but also increase control of the weapon with the sling or bipod deployed.
A soft recoil pad might reduce recoil, but also reduce accuracy.
Maybe there should be some benefits to different lengths of pull, but I’m not sure what they would be, since Unturned player models will presumably all have the same stature. (Some points could include compactness of the stock, length including the thickness of clothing/body armor, and clarity at different distances from the optics.)
Grips
Grips and grip panels with swells, grooves, and texturing give a more secure and repeatable grip, allowing for greater accuracy.
Smoother, rounder grips and grip panels allow the hands to more quickly slide to a firing grip or to reach controls like hammers, slide catches, magazine releases, safeties, fire-selector levers and such.
Birds head revolver grips and grip panels are more on the smooth and round side of the spectrum and allow the hands to slide along the grip rather than being displaced by recoil, creating a recoil pattern with low recoil on the first shot, when the hands have room to slide, but poor recoil control on subsequent shots.
Without any grip attachment, a weapon would be held by the grip frame, the grip screw, the grip tang, the trigger frame, or on ARs a receiver spur and on MGs the rear of the receiver itself.
Grip/Stock interaction
In traditional rifle construction, as well as many bullpup rifles, the stock and grip (and often the handguard as well) are basically always one integral piece.
In pistol carbines, the stock is almost always integral to the grip, or attached to the grip.
In ARs and such, the stock and pistol grip are generally separate, but there are still thumb hole, semi pistol grip, bumpfire, and bullpup attachments that would occupy atleast both the stock and grip slots simultaneously.