Actually, the shape of the patch is of no significance a long as it is perfectly centered on the ball. About the easiest way to make patches is to first lube the fabric and then rip it into strips of the proper width for your caliber of rifle. Properly lubed fabric should have an oily appearance but not have excessive lube on it. As far as the width of the fabric strips, in the case of your .54 caliber rifle, just rip the lubricated fabric into strips 1 3/8 inches wide. Then fold your strip in half and cut it at the fold. Keep doing this until you have your patches all cut to the desired size. You will notice that as you fold, the fabric keeps getting thicker and thicker and harder to cut. Just separate it into smaller bundles to cut it. The final cut may have your patches being just a bit too wide, just trim them to size and you will have your square patches. I might note here that it is vitally important to have your ball perfectly centered on your patch before starting it down your bore. It can be just a bit fiddly getting it perfectly centered. That is the advantage to cutting your patch at the muzzle. But, as you said, you want to precut your patches and this is the best way I have found to do it without spending money for a properly sized punch.