Both the M4 & M16 cylinders are the same, so no need to worry....Here is the date.....
M4 Cylinder: 71.94mm Length, O.D. 25.40mm, I.D. 23.77mm
M16 Cylinder: 71.94mm Lenght, O.D. 25.41mm, I.D. 23.83mm
Both cylinder cam from CA rifles, so as you can see the numbers are about the same.. A bore up cylinder would show diffrent numbers. All numbers done with a Mitutoyo 6" digital caliper.
Also check out the gallery area, you should see my SPR, I built that from a ICS M4 Car-97 and with the M102 spring I get great range and power with it...