Picatinny rails are used to mount accessories to the firearm. These can range from optical sights, to lasers, flashlights, grips, or in the case of devices like the "Mastery Key" even other guns.
Named after the Picatinny Arsenal (where testing was done) the Mil Standard rail permits the mounting of assorted sights, lights and lasers on the weapon.
Yes, as long as your sight you put on it are made for that rail style.
Well, the A2 model has uses the MIL-STD-1913 (Picatinny) rail system, so any accessory which is mounted on that rail system could be used with the L85A2 (and L22A2). In my experiences with the British in Afghanistan and Iraq, the SUSAT sight is still standard fare for line troops, and the soldiers are issued with a bayonet.
Possible, but, very, very, very, expensive.
If it has a picatinny rail you should be able to, so yes, I believe you can.
Well there are a garden variety of rail attachments for your AK, depending on how much money you are willing to spend, you can attach relatively anything to an AK. On my AK I use the rail system on the left side of the firearm to attach a picatinny rail hovering over the dust cover. EO-tech is nice, but very expensive.
With the Picatinny rail mounted variant, yes. But the M320 would more likely be used on the SCAR series rifles.
If you're referring to the distinction between a MIL-STD-1913 Picatinny Rail and a Weaver Rail, your answer is to use a pair of calipers. Weaver Rails have a slot width of .18 inches, with no standards regarding the spacing of slot centres. Picatinny rails have a slot width of .206 inches, with slot centres spaced at .394 inches. General rule of thumb is that, if it's intended for commercial, hunting or other type of sporting uses, it will usually have a Weaver rail, while military styled and tactical designs will have a Picatinny system (to include rifles dressed up as sporting guns, such as the 'Remington' AR15 rifles currently sold at places such as Dick's Sporting Goods). However, Picatinny rail systems are available for commercial sporting firearms and vice versa. In the case of Airsoft weapons, although they try to emulate designs with Picatinny rails, the measurements are probably Weaver, or closer to it, as most airsoft accessories are designed to be Weaver compatible.
The rail is a copy which seeks to emulate the MIL-STD-1913 (also known as 'Picatinny') rail system common to NATO and Western-aligned military weapons. However, it may not be manufactured to the specified dimensions of the MIL-STD-1913 system, but rather, the Weaver rail system. There are three common types of these rail systems: MIL-STD-1913/Picatinny (which is common for military and law enforcement applications), the Weaver rail (which is commonly used for mounting scopes and optics on commercial hunting rifles), and the Diemaco rail (a variation of the Weaver rail first used on the Canadian variation of the M16 rifle). The difference between the two is that the Weaver rail has a slot width of 0.180 inches, with no specifications for the slot centers. The MIL-STD-1913 rail has a slot width of 0.206 inches, and all the slot centers are spaced at 0.394 inches. To determine which of these specifications the rail system is based on would require measurement with a set of calipers. If you are unable to do this yourself, any gunsmith or tradesmith in any occupation requiring the use of calipers should be able to do this.
It's not a guaranteed thing - a lot of times, they will, but there are also a lot of times when they won't.
I believe you're asking about the picatinny rail system. This was designed to allow for the easy installation/removal/changing of accessory items, such as flashlight, scope, sights, lasers, etc.
I'm assuming you already bought the Flatline barrel. That is bad news, since there are Flatline barrels with Picatinny rails mounted on them. Unfortunately, there aren't many ways to mount a bipod if you can't put a picatinny rail on it somewhere.
Picatinny Arsenal was created on 1880-09-06.