Take Roundball's Advice, if you insist on using Pre-cut patches. Go to the next size ball diameter and buy the pre-cut patch for that diameter.
An off-center ball in a pre-cut patch can be very poor for marksmanship. You not only have to worry about having the patch so crooked that part of the ball is rubbing against the lands, instead of the patch, but the edges of ALL patches fray as the fabric is "whipped" back off the ball as they exit the muzzle. You can have the ball go off to another direction if your patch is off-center enough that the fraying affects the RELEASE of the ball from the patch, moreso on one side than the other.
Pre-cuts came about in the late 19th century, when Target shooters used muzzles with squared crowns, and short starters to seat the ball in the patch. Many of these guns had wide, heavy barrels, and enough metal that you could machine a groove in the flat muzzle that would fit the diameter of the pre-cut patch, acting as a centering guide.
Take a look at the bench guns at the firing line at Friendship to see what the shooters use for patches, and how they load them.
The off-hand shooters will be more likely to use strips of fabric, and cut their patches at the muzzle. Their rifles have the more rounded crowns in them.
How to center a patch? I don't know of a "sure way", but I first try to center the patch on the muzzle, without the ball even close to the patch. I hold the ball curled up in a finger in one hand. When I think I have the patch centered, I Hold it in place with a finger of my other hand, while I bring the ball to the muzzle and try to center it in the bore with the sprue UP. If, as the weight of the ball pressing down into the patch indicates that I don't have it centered, I use fingers from both hands to move the patch over to center it, while the ball is resting on the patch.
This whole effort requires the barrel to be absolutely vertical, or the ball will roll off the muzzle! :cursing: So, its a royal PITA to do, IMHO. I am about through shooting all my pre-cut patches, and have bought fabric to make my own strips. I currently have a .50 cal. rifle, and a .62 caliber Fowler, so my plan is to make the strips wide enough to use in the fowler, and use them for my .50 cal. too.
If you don't want to have strips of cloth flapping in the wind, then you can cut SQUARE patches, larger than the bore, and simply trim them at the muzzle with a RAZOR-SHARP knife.
When hunting, I load the gun before going into the field. I don't have strips of anything tied to my pouch strap to flap around in the wind. However, when I used to do shooting matches, and woods walks, tying the strips to the bag strap was a convenient place to have them. :surrender: :hmm: :thumbsup:
My point is, Don't use everything you see at a target range when going into the woods to hunt, or for a long "scout". There are things you can, and should do at a target range that have no place in the fields. :hatsoff: