This might help a bit
For gas basics-
http://en.wikipedia.org/wiki/Gas_operated
Roller delayed
All 7.62mm CETME rifles are built around Vorgrimlers' roller delayed blowback system. This system employs a two parts bolt with two rollers. The front bolt part (bolt head) is relatively light and has a bolt face with extractor on it. It also has a hollow cavity at the rear, in which an inclined forward end of the rear part of the bolt (bolt body) is inserted. The system features two rollers, inserted from the sides into the bolt head and rested on the inclined forward end of the bolt body (see this diagram; it will pop up in the new window). When gun is fired, the pressure began to move the cartridge back against the bolt face. The rollers, which are extended into the recesses in the barrel extension, began to move inward into the bolt head, due to inclined shape of the recesses. This movement translates into the faster rearward movement of the heavier bolt body, so, at the initial moments of shot, when pressure in the chamber is still high, bolt face moves relatively slow. When pressure drops to a reasonable level, rollers disengage the barrel extension completely and from this moment on the bolt head and the bolt body move backward at the same speed, extracting and ejecting spent case and chambering a fresh cartridge on the way back.
From
http://www.world.guns.ru/assault/as60-e.htm
M-16 Gas
The heart of the AR-15 is the direct gas system, developed by the Eugene Stoner in the early 1950s. This system uses no conventional gas piston and rod to propel bolt group back after the shot is fired. Instead, the hot powder gases are fed from the barrel and down to the stainless steel tube into the receiver. Inside the receiver, the rear end of the gas tube enters into the "gas key", a small attachment on the top of the bolt carrier. The hot gases, through the gas key, enter the hollow cavity inside the bolt carrier, and expands there, acting against the bolt carrier and the collar around the bolt body. The pressure of the gases causes the bolt carrier to move back against initially stationary bolt. The linear rearward movement of the carrier initially transferred into the rotation of the bolt, via the cam slot in the bolt carrier and the cam pin, attached to the bolt, that followed the slot. As soon as the bolt is rotated to unlock from the barrel, the bolt group continues its rearward travel under the inertia and the residual pressure in the barrel, extracting the spent case and compressing the buffer return spring, located in the buttstock. The forward movement of the bolt group first strips the fresh cartridge from the magazine and, on the final stage of the movement, rotates the bolt to lock into the barrel extension. The bolt has 7 radial locking lugs, eight lug is located on the extractor claw. Since the introduction of the XM16E1 rifle, the forward assist device is used on all military and most civilian AR-15 type rifles. This device consist of the spring-loaded button with internal claw, that engages the serrations on the right side of the bolt carrier to push it forward, if the pressure of the return spring is insufficient to do so (for example, due to the fouling inside the receiver or chamber). The rifle will not fire unless the bolt is locked and the bolt carrier is in its forwardmost position. The bolt carrier and the bolt itself are chrome-plated. Another feature of the AR-15 type rifles is the bolt catch device, that locks the bolt group in the open position when the last round is fired. To release the bolt group one must push the button, located at the left side of the receiver, above the magazine. The "T"-shaped cocking handle is located at the rear of the receiver, above the buttstock, and does not reciprocate when gun is fired.
http://www.world.guns.ru/assault/as18-e.htm
FAL
It uses short piston stroke gas system with gas piston located above the barrel and having its own return spring. After the shot is fired, the gas piston makes a quick tap to the bolt carrier and then returns back, and the rest of the reloading cycle is commenced by the inertia of bolt group. The gas system is fitted with gas regulator so it could be easily adjusted for various environment conditions, or cut off completely so rifle grenades could be safely launched from the barrel. The locking system uses bolt carrier with separate bolt that locks the barrel by tipping its rear part into the recess in the receiver floor.
http://www.world.guns.ru/assault/as24f-e.htm
World.guns.ru is a great site for gun info, look around in it sometime.
