AS recommended get yourself some loading manuals. One in particular I found quite a bit of data in was the Nosler, but the Lyman is also a good one. Several are better than one to compare load data and bullets with. They will also help out with things like proper forming of the cases, and how to watch for pressure with the break open action.
In working up loads for mine I tried a variety of bullets and powders. I used some bulk 140gr Remington bullets, simply because I had them. They were loaded up using a medium load recommended by the manual. My goal was similar, I was going to use this for an out of state handgun only hunt in big deer country and didn't want to drive a thousand miles only to have to pass on a shot out at 150yds.
I consulted with every manufacturer on what the lowest impact velocities were for the bullets I had chosen, as well as if they had any preferred load data wich would help me reach my goal.
In the end I found that RL-15 indeed produced the best groups and velocity for my barrel, however there were others which were very close. The two bullets I stuck with were both in the 140gr, and were the Nosler Ballistic Tip and the Barnes X. The Barnes while reported to expand to at least double caliber at the lower velocity of the two did not group as well as I had hoped, however the BT shot ragged holes at 100yds, and as long as I could hold it still, to ranges out to 250yds.
I used it on a doe at 283 lasered yards and upon impact behind the onside shoulder it nearly flipped her over. It exited through the offside shoulder leaving a half dollar sized hole, and taking out a goodly portion of vitals with it. She made one leap and piled up.
When I worked up those loads there was only the Nosler which had the plastic tip on them to promote expansion. Nowadays there are several more great bullets to choose from. If doing it again I would possibly look at the 140's from Hornady, Nosler, and Barnes 120 TTSX. I highly doubt you will not find one of them to shoot very accurately. About the most your going to get from your barrel is in the mid 2200fps range with the heavier bullets, possibly mid 2300's with the 120 depending on which powder you use. Out at 200yds this will be down in the 1800fps range and your relying on the expansion to do the job instead of ft/lbs of energy. Of all the detractions from Nosler Ballistic tip bullets over expansion has been one of the most widely broadcast, however this is generally due to high impact velocities with the lighter bullets for caliber. The 140gr has not shown to do this at the lower end velocities and has performed very well. It will also hold more energy and buck the wind a bit better than the lighter weight bullets.
Good luck with your work ups. If possible look through several manuals at the library or one of the local shops. Pick out the ones you find the best or most data in for the calibers your going to load. The ones mentioned are good, but these are based upon personal preferences and data useful to me. Either way the manual(s) are the way to go. Too much internet stuff can be detrimental in some cases.
