APFG/VFC MCX upgrade parts

I don't like how the bolt is riding and wearing down in the APFG MCX upper receiver, so I decided to try and fix that. The whole solution uses an additional guide rod and brass bushings, so it's not an easy mod to do, but it seems that the rod guide stabiliser enough is already reducing the resistance and improving gas efficiency.

You will need two M3x8 grub screws to attach the stabiliser.

For the roller, slight modification of the bolt is needed, as in the pictures. It is clamped in the bolt using a M3x8 countersunk screw and a low-profile M3 nut. The axis is made from a 3x8mm pin, the bearing used is a 623 without the side seals for minimal resistance. 

The "tire" for the roller is best printed from hard TPU and glued to the bearing.

If you would like to add the third guide rod, there is a drilling template tool file included to drill a 4mm hole in the bolt for tapping it M5. The brass bushings are 7mm OD, 5mm ID, 10mm long. The original holes for the guide rods are drilled out to 7mm, where I push in the bushings drilled out to 5.6mm (I know, complicated).

All this greatly decreases slack present in the design while still moving smooth. Hard to judge precisely, but 30% increase in gas efficiency is the minimum I would expect from this upgrade and the bolt is not wearing down so much any more.

I recommend MJF prints, but FDM will work fine also. I can post the non-filleted versions for FDM printing if it will be annoying.