Optimal forcing cone angle?

[Jtarm]

What’s the optimal forcing cone angle for cast bullet accuracy in a revolver?

I know 11-degrees is usually discussed, but I seem to recall reading somewhere that during PPCs heyday, some custom gunsmiths cut them differently, like 6-degree.

[Ramjet-SS]

I think the optimum can be based on the bullet and caliber. Sharp shoulders are not good for accuracy with cast. Lead them gentle like into the barrel and make sure it’s square.

[Bazoo]

I’d like to give Taylor throating a try. My reading shows it always improves accuracy.

[Jtarm]

I’d like to give Taylor throating a try. My reading shows it always improves accuracy.

I just looked it up. There’s a dearth of information on the web, but it does sound interesting indeed.

Are there any custom smiths around who do it?

https://web.archive.org/web/20020606140647/www.sixgunner.com/dad/throat.htm

Well after reading a little more, especially on this forum, looks like it’s not so great for cast bullets as the freebore prevents a gas seal.

[tazman]

Ideally, the forcing cone shape should guide the boolit into perfect alignment with the bore without damaging the nose.
My best accuracy usually comes with a boolit that has a RNFP shape to the nose. The slightly rounded angle seems to fit most forcing cones well. The Lee 358-158-RF works well for me.
Also, a stepped round nose works well as the nose allows the boolit to align with the bore before the shoulder hits the rifling. Think 358311.
I can't speak for every forcing cone shape but this works in my(admittedly older) S&W revolvers.

[DougGuy]

Well, let's look at the purpose of the forcing cone. It doesn't actually guide or "funnel" the boolit into the bore, it causes the boolit to rotate and move the cylinder into best alignment by causing the cylinder to align to the path of least resistance.

The boolit begins to exit the front of the cylinder and it comes into contact with one side of the forcing cone, this causes the boolit to push the cylinder away from the point of contact so the cylinder rotates to lessen the force of the boolit pushing against it.

Ruger SA revolvers have considerable tolerances in the cylinder to frame fit, there is a decent amount of movement when the hammer is cocked and the bolt latch is engaged, this movement may seem excessive to some, but it will make a Ruger last for generations if left alone. You can gunsmith the movement out of it, but it will shoot loose in relatively short time unless the gun is totally rebuilt with align bored chambers so everything is perfectly aligned on each chamber each time the gun is cocked and fired.

Some early S&W revolvers didn't have forcing cones, but they had bank vault tight lockup and they were fitted together by master craftsmen. They had no need for a forcing cone.

As Tazman mentioned, RF profile boolits are a smoother transition and I DO recommend these as well, as the ogive is much more parallel to the forcing cone angle and there is less distortion of the boolit, and less torsional forces against the cylinder and the cylinder latch.

Common with Ruger large bore revolvers is an 11° forcing cone angle, it has good utility with factory and cast ammo both. Many Ruger and S&W 38/357 revolvers have a 5° forcing cone angle, this is a long transition into the bore that reduces pressure because there is less resistance, and boolits are less distorted. The Mountain gun has somewhat of an 8° or 8.5° angle, and I special order 9° cutters that cleans these up nicely without making much of a change in bore geometry.

11° is generally accepted as good for cast, I would prefer 9° if I had a choice.

[dogdoc]

I seriously doubt that it really makes any significant difference . 5, 6 ,or 11. So many variables in how a revolver shoots I cannot see it making a difference. I have rugers, smiths and others. I have even rebarreled and cut different ones. I am not good enough to tell any difference and I bet most who claim it are expressing their opinion or one they heard somewhere else without any scientific method.

[Ramjet-SS]

Well, let's look at the purpose of the forcing cone. It doesn't actually guide or "funnel" the boolit into the bore, it causes the boolit to rotate and move the cylinder into best alignment by causing the cylinder to align to the path of least resistance.

The boolit begins to exit the front of the cylinder and it comes into contact with one side of the forcing cone, this causes the boolit to push the cylinder away from the point of contact so the cylinder rotates to lessen the force of the boolit pushing against it.

Ruger SA revolvers have considerable tolerances in the cylinder to frame fit, there is a decent amount of movement when the hammer is cocked and the bolt latch is engaged, this movement may seem excessive to some, but it will make a Ruger last for generations if left alone. You can gunsmith the movement out of it, but it will shoot loose in relatively short time unless the gun is totally rebuilt with align bored chambers so everything is perfectly aligned on each chamber each time the gun is cocked and fired.

Some early S&W revolvers didn't have forcing cones, but they had bank vault tight lockup and they were fitted together by master craftsmen. They had no need for a forcing cone.

As Tazman mentioned, RF profile boolits are a smoother transition and I DO recommend these as well, as the ogive is much more parallel to the forcing cone angle and there is less distortion of the boolit, and less torsional forces against the cylinder and the cylinder latch.

Common with Ruger large bore revolvers is an 11° forcing cone angle, it has good utility with factory and cast ammo both. Many Ruger and S&W 38/357 revolvers have a 5° forcing cone angle, this is a long transition into the bore that reduces pressure because there is less resistance, and boolits are less distorted. The Mountain gun has somewhat of an 8° or 8.5° angle, and I special order 9° cutters that cleans these up nicely without making much of a change in bore geometry.

11° is generally accepted as good for cast, I would prefer 9° if I had a choice.

Thank you for this excellent information.

[DougGuy]

I seriously doubt that it really makes any significant difference . 5, 6 ,or 11. So many variables in how a revolver shoots I cannot see it making a difference. I have rugers, smiths and others. I have even rebarreled and cut different ones. I am not good enough to tell any difference and I bet most who claim it are expressing their opinion or one they heard somewhere else without any scientific method.

I can pretty much agree with it not making much of a difference, especially if the revolver shoots to the middle of the bore, boolits don't much touch the forcing cone at all in this scenario.

The reason I would prefer a 9° cutter is because many times the 11° cut doesn't clean up the factory tool marks unless and until you start cutting into the fire ring and making it narrower at the barrel cylinder gap which you should NOT do. The 9° angle reaches just a little farther into the rifling without the need to make the fire ring any narrower, in fact you don't even need to cut all the way to the barrel face, considering that 90% of the forcing cone won't ever make contact with a boolit.

[dogdoc]

Good point although I have purchased all the forcing cone gages from brownells and found factory cones often swallow them. Hence the diameter of the beginning of the cone (your fire ring?) is highly variable even among nonmolested forcing cones so the small amount you cut when redoing a cone is likely inconsequential.