Looks much more like an L1A1 to me.
You're quite right. The only metric parts are the receiver and the magazine. FAL action (recoil) springs can be heavy, and you're correct about slingshotting the charging handle. FrankenFALs are as good as the person who put them together.
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.