quote:
Sorry for the noob question but what is a roller lock versus a normal AR?
All semi auto/full auto guns have to use some method to eject the spent round and chamber a new round with only the trigger being pulled.
Roller locks is slang for a style of gun that uses a different operating system than your conventional AR or AK.
(Most) AR-15s operate on a system of direct impingement. Gas is vented from the barrel to a gas tube, which carries the gas back to the bolt carrier, pushing it back, ejecting the spent round and picking up another from the magazine.
AR-15 in operation:
There are a lot of guns (AKs, Sigs, Tavors, FALs, etc) that are piston systems. Gas is vented from the barrel to a tube, where the gas pushes on a piston, which then manipulates the bolt carrier.
Piston system in operation:
Roller lock is common slang for what is more precisely called a roller delayed blowback firearm: A gun with no gas system at all.
The rollers are the circles you see on either side of the red two piece bolt. In the most basic terms, rollers keep the bolt engaged in the chamber until the pressure has dropped enough to safely open the chamber of the firearm. Essentially, roller delayed blowback is the most German possible answer to the question "How do I use the firing of a cartridge to load the next cartridge?" in that it is among the more complicated ways to make a semi auto or full auto firearm work.
So why on earth would you prefer the more complicated system?
Well, for one the gun doesn't require a piston or a direct impingement gas system to work. This is the reason the G3 (Germany's roller delayed blowback rifle during the Cold War) was lighter and shorter than its contemporaries, the M-14 and the FAL.
They also were much easier to free float. While Free float handguards are all the rage now on ARs (and for good reason), the roller lock guns were using free floated barrels for years before other designs, who had to contend with how to free float and protect/secure their required gas system.
Finally, they're pretty dang reliable. Yes, so are other designs, but no gas system means a roller lock gun has one less group of parts to break, malfunction, or be damaged and prevent proper semi auto/full auto function.
The most well known examples are the G3 rifle in .308, and the MP5 series in 9mm, though they can be found in 10mm, 5.56, and 7.62x39 as well.
My first two were a G3 clone and an MP5 clone pictured below: