I should mention, many people starting out have difficulty loading a tight combination - I did when I started. I don't know your experience level, so will suggest some things I found worked for me, and why.
Once I found the biggest problem of the whole loading scenario was the muzzle's factory crown. After I altered that bty smoothing I found could load almost any combination I could think of, including oversized balls in one particularly deep grooved barrel. The crown's machine but corners, were smoothed using the end of my thumb and emery or wet/dry paper - about 320grit.
The GM's normal rifling depth of .010" to .012" easily allows you to use a ball of .445" with a good thick, strong patch. I like .0215" ticking or .0225" denim. The denim I last bought was listed as 10 oz. Some has an oz. designation, while other's doesn't. I take calipers or a mic with me to the yard good store, measuring .001' to .002" thicker than I want and buy the material by the meter. Washing the sizing out softens the fabric and usually reduces is in thickness up to .002". Not all calipers nor micrometers are created equal, except hopefully when measuring hard objects. Soft objects are difficult to get consistent results due to coth compression and the width of the anvils in the measuring device.
I have 2 sets of calipers and all three give different readons on the same strip of cloth when used exactly the same way. This creats confusing measurements - what one person's .020" might be antoher person's .017" - yes- .003" difference in my calipers and the mic measures .004" difference, normally and up to .005" with very thick material. So- pick a method of measuring and get used to it. I find all compercial measurements to be about 002" to .003" over what the material mics for me.
Ox Yoke .018" is .016" when I measure it. So- perhaps m .025" is actually .0245" the way OxYoke measrues cloth?
Suffice to say if you want a seal between the ball and the bore - if the ball and patch combination you are using is going to seal and shoot 'cleanly' with no fouling buildup shot to shot, then you need a fairly thick patch with a ball only .005" or perhaps at the most .010" smaller than the bore. The larger ball will be more accurate than the smaller ball(is in every gun I've shot), once the proper patch material for it is found.
Some combinations have worked in all guns - .005" under bore sized ball and 10oz or .020" to .022" denim material - spit, water or alcohol and water for winter target shooting and Neetsfoot Oil, Mink Oil, Bear Grease of Oil, Marmot Oil for hunting. I have not found Olive oil to work for me - it doesn't keep the fouling soft and isn't as accurate - for me. It seems to work for others so is worth trying.
You will need a short starter. I don't care if our ancesters didn't use one - they didn't know any better, they had no one to teach them to use one, they had no time or nor money to spend on experimentation and they didn't get the accuracy nor clean shooting you will by using one. So- you need a short starter. A chunk of heavy deer antler shaft or moose or elk antler is a good 'end'- 2" to 2 1/2" round hardwood shaft about 2" long orMaple round ball works. I use a chunk of baseball bat for my BIG starter's knob. Ordinary hickory from a broken rod makes the shaft - 5" to 6" protruding.
.45 Green Mountain and .58 Musketoon Crowns
Loading and shooting the .45 Green Mountain barrled rifle - .0225" denim patch and .445" ball. the patch and ball are already sitting on top of the muzzle. I am using the short stud on the rod to put them down flush, then the shaft of the starter to punch them down 5" before shoving them down the rest of the way. This does not take as long to do as to say- or read, as you can see. I've done this before. Some people think using a starter is a slow process - it doens not have to be.
Starters I use. Most have a short stud to put the ball flush or a bit below the muzzle. A smack with the hand accomplishes this task. Then, the cloth can be trimmed off if using strip patching, or punched down the rest of the way with the long shaft. The ball starts evenly if started this way. If merely smacked, as we used to do and still do sometimes, it can start more to one side, pushing up lead on that side and that will effect accuracy. I have never been able to get accuracy with loose ball and patch combinations that do not require a starter. Some have noted they do get good accuracy without using a starter, but that has not bee my experience. I thought it only fair to mention other methods.
