Simple Fix;
Smart move to post photos of your patches
Photos of your shredded patches indicate two possible issues.
Being that your getting tight groups, I suspect the edges of rifling in your bore has sharp burrs that are cutting the patches.
*If it were my rifle, first step would be to lap the bore with steel wool to remove any razor sharp edges on the rifling.
I've used the lapping process below to condition the bore of many new & pitted original guns to make them perform at their best.
SHARP CROWN ?
As others have mentioned a sharp crown at the muzzle can cut patches, consider posting a photo of the muzzle.
Bore Conditioning;
You will need a stout cleaning/loading rod with a swivel 'T' handle, my favorite are steel military surplus .50 cal. cleaning rods. they accept 10-32 cleaning jags. These rods work perfect as a range rods & to condition bores if a tapered sliding brass collar is used to prevent wear to the muzzle.
Treso makes these bushings or can make your own from brass stock.
#1- Depending on condition of the bore, in your case use a .45 caliber cleaning jag & wrap the end with 2-3 or 0004 grade steel wool so it fits tight & lap the bore until you feel even smoothness with no tight spots & finish with 0004 grade steel wool.
- In most cases this procedure resolves blown patches unless your PRB combination is too loose.
#2-Shredded patches like yours could also indicate the patches your using are too thin allowing blow-by gasses to shred the patches.
Fix;
-If you have access to a set of 6" dial calipers, write down depth to bottom of the bore's rifling & same to top of the rifling & post on the forum
& one or more of us will be happy to recommend the correct PRB combination, could be as simple as using slightly thicker lubed patches.
