I hope you have better luck with someone cleaning up the forcing cone that I did with a GP-100. Mine actually looked like someone cut it with a rusty auger. I gave it to a "gunsmith" who was reluctant to cut the 11 degree chamfer and only did it piecemeal awaiting my approval. I finally(after two visits) just got it back from him. He never did it to my satisfaction but it did look better than before. My problem was leading...only at the forcing cone and that was why.
Before
After