Muzzle Velocity and Rate of Fire Results

Piston	Weight (oz)	Average Muzzle Velocity (fps)	Average Rate of Fire (rpm)
ICS Aluminum Piston	0.8	486.93	612.24
Systema Aluminum Piston	0.9	487.26	608.11
Deepfire Titanium Piston (full)	0.7	485.88	633.80

Piston Geometry Measurements

Recent testing results with the Prometheus Hard Piston indicate the importance of piston geometry when parts from different manufacturers are mixed in the same mechbox. Although it would seem reasonable to assume that most manufacturers conform to the stock Marui specifications as closely as possible, it is clear that several manufacturers elect to break the mold and improve upon the stock Marui design. The following table shows various measurements of pertinent parts on the test pistons, with the reference Marui piston measurements at bottom. Measurements were taken with a digital caliper with an accuracy of +/- 0.02mm and a resolution of 0.01mm.

Piston	First Tooth Thickness (mm)	Average Tooth Thickness (mm)	Average Tooth Spacing (mm)	Effective Teeth Height (mm)	Full Rack Excursion (mm)	Rail Width (mm)	Inner Diameter (mm)
ICS Aluminum Piston	4.23	2.36	0.86	9.54	46.73	5.81	15.63
Systema Aluminum Piston	4.03	2.43	0.85	9.63	47.32	5.85	15.67
Deepfire Titanium Piston (full)	4.37	2.46	0.87	9.47	46.72	6.35	15.14
Stock Marui Piston	4.02	2.36	0.83	9.57	47.12	6.29	15.68

First Tooth Thickness
First tooth thickness refers to the thickness of the first piston tooth in the axial direction (along the length of the piston). Since most pistons have trapezoidal teeth, only the thickness at the base is measured. The thickness of the first piston tooth can be an indication of how resistant the tooth is to the impact force of the first sector gear tooth.

Average Tooth Thickness
Average tooth thickness refers to the thickness of the main teeth on a piston in the axial direction. Measurements are taken for each tooth at the base of the trapezoid, and the results averaged.

Average Tooth Spacing
Average tooth spacing is a measurement of the distance between the piston teeth, measured from the base of one tooth to the other.

Effective Teeth Height
Effective teeth height is a measurement of how far the main teeth on a piston "protrudes" into a mechbox to mesh with the sector gear. Since a pistons lateral movement is restricted by its guide rails, this measurement is taken from the top of the lower guide rail to the top of the main teeth. Some pistons have teeth which effectively protrude further into the mechbox, leading to meshing problems with the sector gear.

Full Rack Excursion
Full rack excursion is a measurement of how far "back" the piston is pulled during a full sector gear rotation. It is measured from the "front" of the first tooth to the "front" of the last tooth. Pistons which pull the spring further back should exhibit slightly higher FPS readings due to more compression of the main spring.

Rail Width
Rail width is a measurement of the sum measurement of the width of both guide rails and the guide groove between them. Some pistons have "tighter" rail measurements which restrict piston movement more than those with "looser" rail measurements.

Inner Diameter
Inner diameter is a measurement of the inner barrel diameter of a piston. Most main springs are approximately 14.5mm in outer diameter, while most pistons are approximately 15.5mm in inner diameter, leaving 1mm of free space for the spring. Some pistons exhibit tighter inner diameters which may result in more friction with the main spring and lower FPS and ROF results.