evan: The patch for the .40-.49 will work fine as long as you make sure it is centered on the muzzle as you start the ball. What is needed is for there to be patching material between the outside of the ball and the bore so if you press the ball down into the bore with your finger and there is over 1/16 of an inch of material still sticking out of the area where the ball and muzzle meet, it will work fine.
As for buying material at a cloth store there are several things to keep in mind.
First and formost, the material must be pure cotton. No polyester, rayon, nylon or any other man made material will work. Even a trace of it in the material will melt when the gun is fired and ruin the accuracy.
Second, you want a very tight weave material. Loose weaves like terry cloth just won't do the job.
You want material that is close to the right thickness. Something in the .015-.019 range.
New denum is usually too thick (IMO).
This is why folks around here talk about WalMart "Pillow ticking". It's the blue/white striped stuff and it works great.
If you buy some material it is recommended that you put it thru a wash cycle to wash the "sizing" out of it. Sizing is another term for the starch the cloth people put on it to keep it from wrinkleing. It also is rumored to deposit itself in the bore of your gun if you shoot it.
You should be able to find a suitable material for around $4-$6 per yard. A yard of material will make over 700 patches.
Have fun!
zonie