Deer round...
JKM--I use a 165 grain Sierra Game King over H380 powder. Usually use CCI Large Rifle primers, but others will do. This works great on deer. Accurate as well. H380 has the added advantage of metering beautifully.
Check a published manual for powder amounts--NEVER use anonymous load recipes off the I'net unless they jibe with what a manual or a manufacturers' website recommends. Any anonymous yahoo can put anything they want on the 'Net, and you and your beloved Old Betsy are the guinea pig.
The exact amount of powder that each different rifle "likes" will vary, anyhow. When you use a published load, you start with the recommended "starting load" and work up until the accuracy is acceptable. Stop at the "maximum load" for safety. If you're still not happy with the load, switch to a different powder or bullet, and start over.
My go-to manual is the Lyman's 48th edition, but now they have the 49th out. There are several good manuals available--2 or more, and cross-checking, are even better than one.