For those who know how to weld, making your own portable impact mill / crusher for field use is possible.

I'll scope this thread to gas engines only.

Here are some example builds (not necessarily the 'best', but certainly some of the lightest and most portable:

4 stroke engine - build #1

https://www.youtube.com/watch?v=EFvqLJlrRRw

2 stroke string trimmer engine - build #2 (pan or bucket underneath)

https://www.youtube.com/watch?v=UmVJBJl-Zn4

2 stroke string trimmer engine - build #3

https://www.youtube.com/shorts/lCrf3BQ9VRo

4 stroke engine - build #4 (tow hitch impact mill)

https://www.youtube.com/shorts/0zuhA-8wQ1w.

4 stroke engine - Dodgy home made crusher - build #5

https://www.youtube.com/shorts/f9sBrjEu04A