Different makers use different angles, and custom gunsmith's can alter the cone angle for best accuracy with jacketed bullets or lead.
However, the CRITICAL measurement of a forcing cone is the outer diameter.
Many people get into trouble when altering the cone, or fitting a new barrel, when they don't know that the critical area is the outer part of the "funnel".
If the outer diameter is too large, or too small, accuracy suffers and the gun can spit bullet fragments.
The ONLY way to check the forcing cone diameter is with a special plug gage which is dropped into the rear of the barrel. The cone cannot be "eyeballed".
Since I'm most "up" on Colt's here's the Colt specs for a Python, which is typical:
For the Python Colt uses a .160 taper, which is about 9 degrees.
The outer mouth of the cone must be a minimum of .370, and a maximum of .376.
As you can see, the difference between minimum and maximum is VERY small, and this is why you HAVE to use a gage to measure it.
