I have a Marlin 1895 ported Guide Gun in 45-70. A front sight screw snapped off flush with the barrel. I took it to a local gunsmith to have the screw extracted. When I picked it up, I looked down the bore and saw something toward the muzzle! I asked if he drilled all the way to the bore and he said I don't think so! Upon examination, he discovered that his helper had penetrated into the rifling. He immediately offered to replace the barrel but I told him to hold off until I checked the guns accuracy. What are the risks here? The gun is ported so I know that holes aren't all ways a bad thing but those ports aren't drilled through. I was going to lap the barrel to remove any possible burs and then check the accuracy. Does that screw hole run the risk of a blow out from pressure? Thoughts?