Nice video, but he forgot the most critical part.

The forcing cone is a very misunderstood part of the revolver barrel and even many professional gunsmiths don't really understand them.

THE critical dimension of a forcing cone is not the depth or angle of the cone, it's the diameter of the MOUTH of the forcing cone.
That outer mouth dimension is critical.
Too small and the revolver will be inaccurate and may spit bullet metal.
Too big and accuracy suffers.

An important part of cutting or re-cutting a forcing cone is to use the special drop-in plug gauge.
This precision gauge gauges the the outer diameter of the cone and makes sure it's not too big or too small.
The difference between too big and too small is tiny and you can't eyeball it.
Just cutting a cone blind without using the gauge is what often causes a revolver to suddenly loose accuracy.

This is what many people don't know, so they just cut cones blind.

BARREL CHAMFERING PLUG GAUGES - Brownells