Zippy,
Here's how I work up a load:
Pick your bullet, load up 5 dummy rounds without primers or powder with the bullets seated way out (like 1.7" long). Load them into the magazine and rack them out rapidly. WRITE DOWN the OAL and brief description i.e. "rough", "hangups", "stovepipes," etc. Then go back and reseat them to a deeper OAL like 1.65, 1.63, 1.60, and on down to where you start getting rough feeding again. Write down findings each time or you WILL FORGET the last or best OAL (BTDT). You will find a "sweet spot". Mine was 1.61" for BOTH my Pumas for the SWC and 1.56" for the RN). After finding the right OAL, THEN fiddle with the powder charge from the bench over sand bags at 25 or 50 yds using 3 or 5 shot groups of each charge. I use a muzzle loading 6 bull target and keep a notebook with sections for each gun with a list of favorite loads for each gun including OAL. For the Rossi Pumas I find the best feeding OAL first then work up the powder charge. I use my Rossis exclusively for CAS/SASS matches where reliable feeding is paramount. I also have fire lapped both rifles and groups shrunk by about 30% afterwards. I do the opposite for the deer rifles (get most accurate powder charge then fiddle w/OAL that is most accurate AND feeds well). I've had OAL changes shrink groups by 50% in my 30-06.