Erma E M1 Carbine front sight

[Patrick Chadwick]

...Have you ever seen anyone "break" the lower edge of the chamber mouth? The mouth is a perfectly square, sharp edge...
LTC

Indeed I am seriously considering doing that myself. In principle, all you would need would be a rat-tail Swiss or diamond file, and very, very carefully form a lead-in at the bottom of the chamber mouth. If you look at this area with the aid of an eyeglass, you will see that the edge is** chamfered, but only by a few tenths of a mm - just enough to accommodate the rounding between the rim and body of a .22 case, but quite inadequate for a bullet feed ramp.

Now on a center-fire rifle one would say that to open out this area could be extremely hazardous, leading to case-head blow-outs, or at least serious distortion. But since .22 cases are not reloadable, who cares about distortion as long as the case integrity is not compromised? The rim region of the case is anyway seriously distorted by the striker - that's how rimfire cases work! So I reckon that the chamber edge could be enlarged a few more tenths of a mm. To avoid the lead-shaving effect, the edge profile should not look like this

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which, fortunately, it is not quite...
... or even this

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but rather this

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In other words, a chamfer will still cause some shaving if it has a sharp edge. The edge must be rounded.

The real problem is: How can one achieve this without FUBARing the rifle????

On that, more later...

...I am continuing to proceed slowly so as not to do irreversible harm... LTC

And so am I !


** make that "should be" chamfered. Maybe your Erma is slightly different.