Look at it this way. There is no other fix, and if it hurts your barrel it will be the first on of many thousands that I've heard off.
Accuracy will probably be tightened, but may not, as it sounds like you have a very rare barrel which is tight at the muzzle (and a bit rough) rather than the breach. Lapping will take this constriction out so the bullets don't get a severe grab just as they leave the barrel.
A solution I like for copper fouling is Tetra gun or Tetra lube, which is available at most gun shops. (LBT doesn't sell it.) Be REAL SURE THE GUN HAS A GOOD STRAIGHT BARREL BEFORE USING IT, BECAUSE IT IS NEAR IMPOSSIBLE TO LAP ONE AFTER APPLICATION UNTIL ABOUT 1000 ROUNDS HAVE BEEN FIRED.
Apply it with 50 strokes or so, using a new bronze brush, preferably with the barrel real warm to the hands. I put a thin film of it on each bullet by putting a drop on my fingers and spinning the bullet in them, after loading. The drop on the fingers will be enough for maybe 3 rounds, then add another drop. If the bore is lapped, you'll get little or now fouling after this treatment, and a real plus is better game performance, because the bullet jacket isn't heated and weakened as much by bore friction. This improvement in game performance will be most noted at ranges of 100 yards plus, where the heat has had time to penetrate through the jacket.
So you and the world knows: When high velocity jacketed bullets travel through a rough bore, and especially if the bore tends to foul or is fouled heavily, the surface of the bullet melts, which transfers a bit of copper to the bore, of coarse. But just the surface is molten, and at bullet speeds, it takes a bit of flight time for this heat to travel through the jacket and weaken it. When the problem is severe, bullets blow up in flight with the fast varmint ctgs, or blow on contact with big game, causing an ugly wound which often kills slowly. The woods are full of hunters with guns which don't kill cleanly because of this problem, but it is easily solved.
I'm sure glad you asked because it allowed me to spread this little known wisdom on a cast bullet forum. As far as I know, I'm the discoverer of this problem. I've never read a word in print on the subject. -- Believe me, it is a serious problem. I have two elderly neighbors who aren't savy on keeping barrels clean. One lost four deer and another 14 in one year! When I told them the solution they both got 100% penetration and instant kills on the next deer they shot. Those are only two of many in my experiance. Most hunters just think they missed the animal, or the gun isn't up to the task, so they buy a more powerfull gun, which multiplies the problem once it fouls.
