Hello!
Recently on 16 gauge Low Pressure Loading Group site we have an instance where chamber cast of a 16X67 chambered drilling showed the last half CM or so of chamber to be tapered from about 0,732 to 0,711. This is in addition to standard linear taper from base of head to area where diameter is decreased to 0,732 (as shown on American dimensioned drawing of 16 gauge chambers). These drilling chambers would not fully accept American 16 gauge chamber gauge, with the chamber gauge indicating chambers about 2 1/4 inches long. I have some old German and Swedish hammer doubles from early 1900s that also will not accept American chamber gauges, in both 12 and 16 gauges. To all appearances my guns have never had the chambers reamed, certainly not to 70 mm with American chamber reamers. I shoot normal 65 and 67 mm ammo in them and have done so for decades. Is this taper at front 1/2 cm of chamber a common feature of early 1900 German and Swedish shotguns? How about Belgium, French, Itallian, etc.?
The only rational explanation I have for such chambers is that the taper at last 1/2 cm is intended to provide a tighter fit to fiber wads just as they are leaving the hull and entering the forcing cone. Sort of a dual forcing cone, first part in last 1/2 cm or so of chamber, second part in front of chamber. Unfortunately, chamber cast of that drilling chamber does not show end of forcing cone and start of bore, thanks to shortage of chamber casting material.
Can anyone here contribute more information, explanations to this?
Thanks,
Niklas
