While I was looking for resources on prehospital amputation, I came across the videos below from the Trauma surgeons of the Medical College of Wisconsin. They also have a webpage specifically for the procedure.
Field Manual
Here is their field manual that describes the procedure
Introduction and Background Video
Upper Extremity Video
Lower Extremity Video
Review Article
Cliff Reid has a post on the procedure, that pointed to this article:
Porter KM. Prehospital amputation. Emerg Med J. 2010 Dec;27(12):940-2.
Gigli Saw
Sydney HEMS has a video of an amputation of a deer leg
References
I discovered this article thanks to the excellent Trauma Professional's Blog:
In-Field Extremity Amputation: Prevalence and Protocols in Emergency Medical Services. Prehospital and Disaster Medicine 11(1):63-66, 1996.