I hope you meant one and one-quarter inch strips.

I had a Renegade once that really acted wild on the range. It would shoot all over the place. I learned that it was because I was a bore butter user and the barrel was basically filled in with that stuff. I boiled out the barrel using boiling hot water. Wear leather gloves. Take the barrel out of the stock. Just pour that boiling water into the barrel until it over flows. A tea kettle works perfect. Then dump it out, pour some dish soap down the bore (something that cuts grease) and with a brush on the rod scrub that bore up and down about fifteen times. Now back to the boiling water and fill that barrel. If there is bore butter in it now, it will float up and out the barrel. Also this washed the soap out of the bore.

After all this, pour some isopropyl alcohol down the bore. A good slug of it too. Let it run out the bolster. Now start dry patching the bore. Do this until the patches come out dry. Now you need to oil that bore with a good gun oil.

Before you shoot next time just run a isopropyl alcohol patch down it to remove the oil, then a dry patch or two. Push a dry patch to the bottom and pop caps until you have burn marks on a patch.

I did this and my old Renegade's accuracy came right back.

Just something you might consider.

I think the rifling is cutting the patches...

When you said the .015 is fine but the .018 is getting cut
because it was so hard to load...

Think of this...I've been to shoots where some of the shooters
were using a ball the same caliber of the bore and hammering
the ball and patch down the barrel without cutting the patch...

Take a close look at the lands of the rifling at the muzzle, I've
found burrs there that could be removed with emory cloth...