the springguide on decompression cycles - you carry more of the back reaction to the receiver and your shoulder, which will move less, meaning more of the decompression momentum energy of the spring is transferred to the cylinder's velocity = morefps. Its minute, so its up to you. I personally like the idea of the gun's body structurally supporting the springguide on it's center axis. Some may feel this is not a big deal or worth it. I've yet to have my gun fail in a single event over three hundred thousand rounds, however. Either way, take it for the anecdotal advice it is. ---------------- Inner barrel - this is a CA thing. Specifically a MkII thing. I wind some electrical tape around my innerbarrel at the end for a snug fit inside the outbarrel. Yes there are some spacers in the in a couple places down the length of the barrel to locate it, but after I locked my saw onto a shooting bench and checked it out I got much tighter groupings with that little bit of tape providing extra rigidity. Also - it helps keep water and dirt and mud out of the outer barrel's interior. Clean = good. ---------------- Allen wrench - Keep an allen wrench taped to the inside of the pistol grip inside the compartment there if your gun has it. That way you can change batteries bia the buttplate in the field without having to go back to your car for the tool.