Erma E M1 Carbine front sight

[ltc]

Patrick, Thanks for your insight on my cycling issues. I think a good cleaning is called for. Have you ever seen anyone "break" the lower edge of the chamber mouth? The mouth is a perfectly square, sharp edge. I am continuing to proceed slowly so as not to do irreversible harm.

LTC

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[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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XXXXXXX
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XXXXXXXXX

but rather this

XXXXXXX
XXXXXXXXXX
XXXXXXXXXXXXX
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX

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.

[Sentryduty]

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????

Would it be possible to get a dremel rotary tool with a 90 degree attachment into the chamber? If so, I would start with a conical felt polishing bob and a compound, finishing with a polish, it should round the chamber lip very slowly without resorting to possibly ruinous bit based grinding.

I had a Norinco Type-97 NSR that needed the feed ramp reprofiled to run with non-Norinco magazines and undertook a similar smoothing process. The Norinco magazine fit tightly in the magazine housing and the rounds made a smooth jump to the chamber. Non-Norinco magazines would rock fore and aft which changed the presentation of the next round, often tipping into the feed ramp and ramming the projectile well into the case with extreme force. In my case I started with jeweler hand files and finished with Dremel felt polishing.

[Patrick Chadwick]

Would it be possible to get a dremel rotary tool with a 90 degree attachment into the chamber? If so, I would start with a conical felt polishing bob and a compound, finishing with a polish, it should round the chamber lip very slowly without resorting to possibly ruinous bit based grinding.

That's just what I was thinking of doing, but haven't yet summoned up the courage. Your success with the Norinco is encouraging.