As I read the various threads regarding recoil, cleaning, dirty brass, and after market parts I realize that not everyone understands the mechanical issues of a blowback design. (If you do then skip this thread)
First, a blowback weapon utilizes the spent cartridge case as a piston to cycle the action. This is why most blowback weapons do not have a locking bolt and the brass is so dirty.
To keep the weapon from “running away” and venting burning propellant outside of the chamber the cyclic rate of the bolt must be slowed down. There are two main methods to this: friction as the Thompson Machine gun uses and inertia as found in your Sub2000.
However, this results in two very different “types” of recoil: gas and mechanical.
Your muzzle brake redirects the forces of the gas at the end of the barrel up and back, thus pushing the weapon down and forward…this method will counter the effects of gas recoil by providing a counter force. This will do nothing in regards to mechanical recoil!
That heavy counter weight moving back and forth in your Sub2000 generates some significant mechanical force. You can slow it down by adding more weight, or you can cushion the impact by adding a buffer pad.
Keep in mind that by increasing the mass you are reducing the cyclic rate and trading a fast “whack, whack, whack” for a heavier, but slower “thump, thump.” (Sort of like the difference between shooting a 9mm vs a .45acp). This is exactly why KT makes a heavy counter-weight optional part and MCARBO makes the heavy charging handle.
You are also increasing the load on the return spring. This will result in the spring over time weakening faster and you will eventually see your mechanical recoil increase as resistance is decreased!
Another issue is that while the Sub2000 relies upon inertia, there is some friction between the mass of the moving parts. Excessive polishing of the receiver tube and bolt group (or just time and normal wear) will also increase your felt mechanical recoil.
I know this is basic mechanical physics for many, but I hope it might help some of my brothers whom might not have the same background.