How do you fit

[jcj54]

a replacement cartridge retainer in a remington model 12 .22 pump.
New part oversize but where to remove metal?

 

[Roughedge]

Do you have the old one to use as a guide? If not its a little at a time.

 

[g.willikers]

Some caution is required when fitting new parts.
You don't want to exactly duplicate the shape of the old one that might be worn down.
Like Roughedge sez, easy does it or the new one might turn out like the old one.
Just a thought.