Check on HOW they were supposed to be before you start filing and stoning away.
Any of mine that are in decent shape show standard double-pull trigger: soft at first, then coming to a definite stop, followed by a harder, very short letoff squeeze.
Trouble with the basic MN design is that the spring and sear are the same part and so hardened quite efficiently. Takes careful work with a STONE and OIL to slick one up, but it can be done. Real easy to go too far, too.
Hope this helps.
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