automagsUK.com: Classic and RT Tech Guide

The level 7 parts are the bolt and all the guts inside of the powertube including the powertube tip that you see in the valve picture above. The level 7 is a system of compensating for the crude tolerances that you'll run into if you try to install aftermarket parts like rails and trigger frames. It's one of those things that if it's working, dont mess with it cause you have no reason to.

If your getting bolt stick, put in a shorter power tube spacer

If your getting barrel leak, put in a longer one.

The spacers adjust where the pin inside the bolt seats on the power tube o-ring. You want to have it set where the bolt pin can get past the seal of the o'ring, but also seat far enough so it seals and keeps the dump chamber from leaking while it refills for the next cycle.
Powertube Spacers