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Mike,

Won't such a change take the face of the breech block out of perpendicular with the bore?

I would think it better to re-work the breech block and striker to center fire configuration.

Curl

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Mathematically there is a change in the angle.

Here is the drawing for the .22LR.



Here are the numbers for the math. To do the numbers you will need to use radii.

.22LR is .272” in diameter, .136” radius.

BSA.22 striker is .190” diameter, .095” radius

When properly adjusted the outer diameter of the striker should contact outer diameter of the cartridge, with the striker impact inside the rim diameter. That is the basic rule of thumb. There are other theories for this especially among target shooters, but this is the basic rule.

The center of the striker is .095” from the outside diameter of the rim, or .041” from the center. That means to change from rimfire to center fire the block must be moved .041”.

Now I long ago lost the capability to do these trigonometry functions in my head, so today I jumped to http://www.cleavebooks.co.uk/scol/calrtri.htm and plugged the numbers in.

The length of a BSA .22 breechblock from center of pivot pin to face of breech block is 2.3”. The amount the block must move to change from rimfire to center fore is .041 The angle of the breech face changes 1.02 degrees.

This breech face angle change is based on an assumption, that the breech face was perpendicular to start in the rimfire position. They often are not.

My first encounter with squaring of the breech face was from target shooters who wanted there rimfires squared. Of the number of these that I have “squared” back in my working days, the effect of squaring was never perceptible. But the target shooters were convinced it made a difference.

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DD, Ret.

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