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12/76 patroner i 12/70 kammer


Triggern

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http://hunting.about.com/od/shotgun/l/aastshotgunfaqb.htm

Punkt 12 gir en ganske kort men anstendig forklaring.

 

No. 12

If A Three-inch Shell Fits In My Gun's 2 3/4-Inch Chamber, Can I Fire It Safely With The Longer Shells?

The barrel of my 12-gauge shotgun is marked for 2 3/4-inch shells only, yet a three-inch shell will easily slip into its chamber. Does this mean it is safe to shoot three-inch shells in my gun?

 

Absolutely not. The linear dimension used to identify a particular shotshell refers to the length of its fired case and not that of the loaded round. Actual length will vary slightly among various brands of shells, but those designated as 2 3/4 inches usually measure around 2 5/16 inches before firing and 2 5/8 to

2 11/16 inches after firing. Three-inch shells usually measure from 2 1/2 to 2 5/8 inches before firing and lengthen to just under three inches when fired. Since the 2 3/4-inch chamber of a shotgun will usually measure at least that long, and sometimes slightly longer, you can see how an unfired three-inch shell will drop right into it. Firing shells of excessive length for the chamber can generate dangerously high pressures for the following reason: The inside diameter of a shotgun barrel rapidly becomes smaller just forward of the front end of the chamber in an area called the forcing cone. When a three-inch shell is fired in a 2 3/4-inch chamber, its crimp section opens into the forcing cone and in doing so effectively reduces bore diameter at that point. If the shot charge and wad column are required to squeeze through this partial obstruction, chamber pressure can increase.

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