FM-9 charging handle angled down

I like Foxtrot Mike's FM-9 side charging upper (except for [the usual AR9 feed issues](https://blowback9.wordpress.com/2021/10/22/9mm-ar-troubleshooting-guide-simple-blowback/#TS2)), but the stock charging handle was not designed to work well with anything mounted on the rail above it. Luckily, a couple of other people have already designed their own charging handle replacements, which I was able to easily tweak to allow me to mount an iron sight above it.

My design is a simple remix of [skippymcneal's](https://www.thingiverse.com/thing:4762108), which is in turn a remix of [Jcolasante's](https://www.thingiverse.com/thing:4692563) design. I've simply angled the handle down 30 degrees instead of up 30, shortened it by 25mm, removed the top 2mm above where the handle plugs into the charging rod, and removed 0.1mm from the bottom and left sides of the rectangle which come into contact with the charging rod to improve fit - previously I had to file it down to fit, but now it pops in wit