For cylinder conversion systems we assign numbers to the nozzles instead of using the rifle model. This is because the nozzle length can vary between the same gun model when made by different manufacturers. This can be from the manufacturer designing the rifle differently, or from the thickness of the gearbox shell affecting how far from the hop-up chamber the cylinder sits. Therefore one nozzle length may work in different rifle models but not necessarily work in the same model from a different manufacture. For example, a standard MP5 could require any of 4 different nozzle lengths depending on the manufacturer. Num Most Commonly Used With Tip 1 (Unmarked) TM M4/M16, TM MP5 A/SD, ICS MP5 A/SD, G&G KAC SR-25E2 0.841 2 CYMA AK, CYMA MP5 A/SD, G&G UMP 0.882 4 G&G GR-25 1.466 5 ICS SIG 550/551/552 0.979 6 KA FAL, TM MP5K, A&K M240 0.910 7 PTS Masada, CA SCAR-L 1.150 8 VFC SCAR-H 1.523 9 E&L AK, S&T TAVOR 0.892 11 CA KAC LMG, VFC MP5 A/SD 0.763 12 LCT AK-47/74/M 0.851 13 A&K MASADA/ACR, CYMA SR-25 (V2.5 Kythera SA) 1.362 14 KA CZ 805 BREN 1.405 15 JG G36 1.070 17 CA AUG 1.020 21 Elite Force/CYMA MP5K, CA SA58 0.938 K1 A&K/JG SR-25 (V2.5 Kythera SA)  1.314