Manual

Figure 11-Gauge, Chamber Length and Choke Designation
Chamber lengths are identified by the numeral 70 or 76. The
numeral 76 designates a chamber length of 76mm which is equal
to the English measurement of 3 inches. A barrel marked with
the numeral 70 designates a chamber length of 70mm which is
equal to the English measurement of 2
3
/
4
inches.
Use of shotgun rounds with chamber lengths shorter than the
shotgun chamber length is acceptable. However, never use rounds
with chamber lengths greater than the length of the shotgun
chamber. For example, do not use 3 inch shells in a shotgun
chambered for 2
3
/
4
inch ammunition. In the rifle barrel of your
drilling always insure that you are using the proper caliber ammu-
nition. For example, do not use .270 Winchester ammunition in
a rifle barrel chambered for 30/06 Springfield.
Chokes are identified for each barrel below the designation for
gauge and chamber length on the underside of the barrels. Choke
designation indicates the dispersion pattern characteristics of the
shotgun bore. The chart on the following page provides identifi-
cation for choke and a pattern percentage within a 30 inch circle
at specified ranges.
Gauge or Caliber
Choke
Designation
Chamber Length
27
Drilling Rifle Caliber