Friend's routing above sounds great. I also warm up before shooting. Of course you're not going to do anything to warm up before a hunting shot, that's not the point. I want to minimize any injury potential during practice sessions so that I'm healthy enough to pull off that cold hunt shot without straining.
That being said, stretching alone is not a good warmup. Stretching a cold muscle may actually result in micro-tears in the muscle fibers and connective tissue, that when healed form scar tissue and actually make you less flexible and increase the chances of future injury.
Your best bet is to perform movements that closely approximate the motion to be done in practice, and to engorge the muscles with blood. This makes all muscles, tendons and ligaments better able to handle the stresses.
30+ years of martial arts training has taught me these things the hard way.