Air Compression Assembly

A common claim is that compression parts must all come from the same brand for best results. That is not true on this platform — most brands have one bad product in their lineup, and asking around (or testing in-shop) is more reliable than brand loyalty. The assembly itself is straightforward; the discipline is in the grease selection and the leak test.

• The compression parts selected in chapter 1
• Silicone O-ring grease or Insidious Armory grease (either works on O-rings — never gear grease on O-rings)
• The aligned piston assembly from chapter 4
• Gearbox shell, cylinder, cylinder head, and air nozzle

Match the cylinder type to the inner barrel before installing anything. A mismatched cylinder bleeds compression past the port at the wrong stroke position and costs 20–60 FPS that no spring can recover. We default to 3/4 cylinder on this platform — we have measured ~40 FPS gain over full cylinder, and the first ported step up from full is the worst-performing volume in our testing.

1. Apply one small drop of silicone or Insidious grease inside the cylinder. Spread it evenly across the bore with a clean finger. A film, not a coating.
2. Apply another small drop around the cylinder head O-ring(s) and the cylinder head stem. Light film only.
3. Press the cylinder head into the cylinder by hand. It should resist a few pounds of push and seat with a soft pop.
4. Slide the air nozzle onto the cylinder head stem.
5. Cycle the piston and nozzle by hand 20–30 times. This evens the grease film and seats the O-rings. Any "easy spot" in the stroke means the cylinder bore is scored — replace the cylinder.

After the compression chain assembles cleanly, address the angle of engagement so the first sector tooth lands on the modified rack at ~90°. Two approaches:

• AOE washers — preferred. Steel/aluminum, rigid, repeatable, and they hold AOE across the service life of the build.
• Sorbothane pad on the cylinder head face — sound-deadening, but compresses across thousands of rounds and the AOE drifts. Use only when the customer's priority is the quietest possible build.

Exception: the Real Deal Ultimate Performance piston is pre-AOE-corrected (body is 3mm longer than TM spec). On that piston, install zero washers and no sorbothane — adding either over-corrects past optimal AOE and back into rack-shear territory. You still re-shape the rack (remove tooth 2, angle tooth 3 at 45°) — that's a separate concern from the body length.

With cylinder, head, nozzle, and tappet installed in one shell half:

1. Plug the nozzle with a fitted adapter on the syringe.
2. Push the plunger to 30 mL of compression.
3. Release. The plunger must return to ≥ 28 mL within 1 second. Any less is a leak. Isolate by re-seating the head O-ring first, then the piston-head O-ring, then re-checking the nozzle for a burr.

Reference video: https://youtube.com/shorts/FRAK1uRWU8Y