Snug as a nub. (Barrel Installation)
Installing an aftermarket inner barrel is pretty simple and mostly a harmless procedure, but like most operations, a closer look at the body before performing any surgery can reveal a lot! Let's take a look at the MK23 hop up assembly!
Below, we have an example of how the standard MK23 barrel and hop up components sit in the hop up assembly. Nothing out of place, right? Notice the groove to the left of the hop up rubber. That groove serves the purpose of helping to keep the barrel in a fixed position and helps to prevent rotation.
The problem with the majority of barrels that are not specifically stated to be produced for the MK23 (generally anything longer than 133mm) is that their groove placement is further along the barrel, which becomes a problem when we see how the hop up assembly looks beneath the barrel.