Anything that you can do to improve the efficiency / smoothness of the GBB system will improve accuracy and overall performance of your replica. Here are a few of the updates I have done.
Bolt Polish
Feed Ramp Polish
Piston Cup Mod
TDC Hopup
Lets start with bolt polish. This modification makes the bolt slide much smooth inside of the upper. It's crazy how much of a difference it makes.
Complete unpolished bolt. First, disassemble the BCG.
I used a polishing wheel in a drill press. You can use a hand drill as well.
Here is a small section that has been polished so you can see the difference.
All polished and cleaned, all buffing compound is removed. Also notice the piston with the cup mod to the right.
Here are a few videos I took when I was showing Grounded how perform the mod on his LM4
Polishing the outside of the bolt
Also important, the inside of the bolt where the piston does its work.
Lastly, the finished and assembled product.
