[Stealth]

John here

Here's my braindump for something like this:

Don't touch the nozzle and tappet plate if you have good air seal. Keep those parts. VFC ain't that bad.

Check airseal before attempting anything else. I assume your prommy hop up stuff is all new, so replace one part, chrony, and replace another. Keep doing this until you get exactly the same FPS and a deviation of less than 5FPS. Be extremely cautious of feeding issues. There's no point attempting DSG if you can't even get a SSG to feed properly.

Shimming will be crucial. Some mechboxes require modifications to fit Siegetek gears, but I don't think VFC boxes will need it. Bevel-pinion method for shimming. Moe grips are larger than normal, so shove something inside so the motor stays where it is supposed to.

Take some high grit sandpaper and sand all the piston rails and tappet rails. It must be perfectly smooth and offer zero resistance to the piston. Test fit all moving parts.

Lighten the piston by swiss cheesing it. You also need to dremel off unnecessary teeth.

Make sure the piston doesn't get stuck inside the spring guide spacer.

AoE correction is a given.

ARL needs to be modified.

Before assembling the upper half, test and listen to how the gears sound. I've started using a watt meter to quantify the quality of my shimming. We just got a bunch from HobbyKing and they're a must-have tool for any gun doc.

Reassemble, but use the weakest battery you can find. Make sure your air seal is still good, and you're properly feeding every single round. If it jams, your piston's done. Slowly ramp up your ROF on the MERF as you go. Monitor current draw using the watt meter.