Introduced in the mid 1980’s the Mobilchoke tube system was first available for the model S687L over and under and later carried through virtually every model of fixed breech and semi-automatic shotgun. At this time the Mobilechoke is the only choke tube system adapted by Beretta to 12, 20, 28 gauge and .410. The Mobilchoke system continues to be the mainstay of the 680 series field grade over and under shotguns.
The conical parallel design of the Beretta choke tubes creates a more gradual taper inside the choke tube which gently transitions into a parallel section that runs to the muzzle end of the tube. The conical parallel design results in reduced shot deformation, improved pattern uniformity and increased pattern density.
The following pertains specifically to 12 gauge Mobilchoke tubes. While the dimensions noted will very for the 20, 28 gauge and .410 tubes, identification is very much self evident.
Barrels that use the Mobilchoke will typically be marked only with the gauge marking.
Mobilchoke choke tubes will be marked PB or ST and the degree of choke. If the choke tube is steel shot compatible it will also be marked SP .
The start of the threaded portion of the 12 gauge Mobilchoke tube is located a nominal 41.5 mm (1.63 inch) from the breech end of the choke tube.
The length of the threaded portion is a nominal 9.15 mm (..360 inch).
The major diameter of the choke tube thread is 20.62 mm (.811 inch).