Ideal angle for revolver forcing cone

I finally broke down and took the gun to the gunsmith. At over $100 for the tooling to cut the forcing cone, I deceided it just wasn't worth it. What finally got me motivated, was that I did some serious shooting from my Ransom rest. No SWC bullet would group worth a crap. 3 to 4 inches at 25 yds was common. Truncated bullets shot a little better, 2-3 inches. I used Bullseye, 231 and Clays powder for testing, and the Lyman 452460, 452389 as my SWC bullets, and the SAECO 67 as my truncated bullet. The gun spit considerably when fired. I felt the shoulder of the SWC bullets coming out of the .455+ cylinder throats, was cocking slightly going into the cylinder throats causing degraded accuracy with the spitting, while the truncated bullet as it had no shoulder to catch on, it made the transition more smoothly, with less negative effect. The gunsmith measured the forcing cone with his plug gauge and found it was badly out of spec, without hardly any taper. He cut it while I waited, with a 11 degree cutter, and removed a good bit of metal. He only charged me $16 for the job. Next time I shoot it I will give a report.