They key is to take a shot and try reloading as fast as you can. This will tell you what you need. I put one of those butt stock cartridge holders on my #1 without really knowing what I do after the shot. When practicing, I realized that I bring my rifle down pretty low to work the lever - so low, that my trigger hand is just as close to a shirt pocket as it is to the cartridge holder. The big difference...I can shut my eyes (or keep them on my target) and still get my hands in a pocket every time. With the cartridge holder, I had to look down to find a cartridge everytime. That made up my mind for me.
