Delrin POM Air Nozzle for AEG
With dual internal o-rings, orientation flange and enhanced loading lips
 
Compatible with:
Most M4/G3 : 21.2mm
Most AK / G&G MP5 : 19.7mm
 
This design allows smooth loading of the bb against the bucking patch which provides more consistent hop while avoiding deformation as long as the airsoft RIF isn't miss-feeding.
Installation tips:
The EPN nozzle has an extra chamfer for reinforcement so some hopup may require modification.
To optimize your nozzle to bucking seal, you may need to chamfer by cutting/sanding a 45 degree slope on the inner tip of your hopup.
The nozzles are made like this on purpose and this tiny mod was known to be possibly needed already