Shotgun chamber recess??

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montveil
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Shotgun chamber recess??

Post by montveil » Tue Jan 05, 2010 4:14 pm

I have a 410 shotgun and it has a "recessed" 3" chamber--What I mean is the chamber is larger than the bore. None of my other 12 ga have this feature.

What is this type of chamber called?
Why is it made that way?
How does it affect performance?

Thanks for any help

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Bullseye
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Post by Bullseye » Tue Jan 05, 2010 11:08 pm

Your shotgun chamber is sized for a maximum 3" long cartridge. It is .410 caliber or 67 gauge. The "recessed" term means that the chamber is recessed so that the metal rim of the cartridge is beneath the edge of the chamber and does not stick out. The area you are seeing is the forcing cone area, much like in a revolver cylinder, where the bore is tapered down to the exact dimensions of the wadding. This basically ensures a good gas seal on the wadding cup and prevents gas blow by. The chamber diameter is slightly larger because the outside dimensions of the chamber must account for the plastic or paper shell which is wrapped around the wadding at the end of the cartridge. The cartridge overall diameter is .465" but the bore is tapered down to .410". The forcing cone may be more pronounced in your 410 because this bore is typically a full choke to get the maximum performance out of a relatively small amount of shot in the cup with a tighter shot pattern.

Here is a good picture of what a typical shotgun chamber looks like.

Image
from http://www.dave-cushman.net/shot/shotshellloads.html

The length of the chamber (E) is such that you can shoot 2" 2.5" and 3" long shot shells in your barrel.

Hope this helps with your questions.

R,
Bullseye
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