Greeting ss1,
What make of barrel do you have?
If you have a wide groove barrel like a Green Mountain, the GM folks recommend a .395 for hunting and a .400 for target work.
Patch material measuring .018" - .020" will work just fine for either size ball.
Rabbitt03 is absolutely right about loading your most accurate load for the first shot when hunting. Most likely that will be the only shot at that particular animal, so make it count.
Before buying any Teflon coated patch material, I would suggest working out your most accurate load(s) using lubes like Hoppess 9 Plus, Lube 1000, etc.
Once you have established what is the most accurate ball/patch combination for you, then you are in a better position to choose what thickness Teflon coated material to purchase.
Also know that even with a tight ball/patch combination, Teflon coated material loads much, much slicker and easier than any other patch lubricant.
I have never used a loose fitting ball/patch combination for hunting or competition.
Best regards and good shooting,
John L. Hinnant
If you are not an NRA or NMLRA Member, why not? I am carrying your load.