Erma 22LR magazine fit
 

Q. So what does one do when you get a brand new (to you) gun that comes with a single magazine?
A. Start the search for additional magazines.

I bid on an Erma .22LR missing it's extractor …
after checking and finding a source for a replacement extractor.

OK, get the gun, get the extractor and fit it (with a little help from Ithacaartist)
Reading on another forum I get a chamber reamer and ream the chamber

I now have a nice little shooter, but still with 1 magazine.
I find and get 2 spare magazines.

They appear identical to the original but will only go into the mag well ¾ of the way
My micrometer shows the spine to be a smidgen (Tech term) wider.
I use a vice to compress the spine slightly, and yes it goes into the well a bit further,
but the mag base will not fit and will not compress.

I am thinking of dropping out the base(s) and reducing them but would appreciate any tips

Geoff, I've encountered both under-size magazine wells and a variety of overall related dimensions on their mags. I did a check fit of all my KGP69 mags in all my KGP69 pistols. I came up with effectively Large, Medium, and Small in both categories, and paired the mags with the pistols they fit, marking SN of each gun on the mag(s) that fit it.

Don't modify that mag any further because it simply "belongs" in a KGP69 that happens to have one of the Medium of Large mag wells. The luck of the draw will eventually provide you with a mag that fits nicely, so buy some more and sell this one until you have some that work--which is what you want.

In the case of a mag that "allllll-most" fits, a 1/2" square file works great to carefully shave the rear of the mag well a bit. Keep watch of the subsequent raw metal so it doesn't corrode!