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Old 10-08-2010, 09:25 AM
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Match Chamber versus Standard Chamber

Originally Posted by Milhous Jr View Post
This is where my question lies:
It seemed to be somewhat difficult to chamber a round all the way.
I know these guns are supposed to have tight chambers,
but is this normal?
No, it is not normal for a typical off-the-shelf American rimfire.
But, it is an indication of a match chamber.
Match chambers have tighter/closer dimensions than a standard chamber.
A standard chamber has looser tolerances to ensure reliable functioning
in adverse conditions and/or with all brands of ammunition.

Originally Posted by Milhous Jr View Post
Second, upon examining the rounds after extraction,
the driving band seemed to have noticeable markings from the rifling.
Is this normal?
Match chambers in rimfire applications do allow the bolt to drive the bullet
to engage the rifling.
The combination of tight chamber and engaged rifling makes
for extracting a non-fired round difficult.

In some cases, a match chamber can be so tight and the rifling engaged
so well that an attempt to remove the unfired round will cause the extractor
to slip-off the case rim.
Repeatedly cycling the bolt will end the same way.
The net result ... the unfired round is stuck in the chamber.

Originally Posted by RET View Post
2. Marking on the bullet tell you that your rifling engages the bullet upon chambering.
Accuracy wise, that is generally a good thing....
But take heart, as RET has stated the combination of a tight chamber
and engaged rifling will serve to enhance accuracy.

Here's another simple experiment to try.
Take a spent case for one of your American guns.
And, manually try to chamber the fired case into the Wildcat chamber.
Do not drive the spent case with the bolt ... use your fingertips.
I think you will find that the case will not enter the Wildcat chamber.

Why? The spent case will have expanded to the dimensions
of the chamber it was fired in.
It will have expanded so much, it may not be possible to enter
a match chamber without significant mechanical advantage.
That is, being driven and cammed-in by the rifle bolt.

This simple experiment will help you distinguish a standard chamber
from a match chamber in the field.
W. Edwards Deming ... Quality: It is not enough to do-your-best;
you must know what-to-do, and ... then ... do-your-best.
Ever-Onward ... Through the Fog ---- Fort Stockton TX 79735
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