Compound Forcing Cone Angles?

[Caballero59]

One of my Ruger Flattops in 45 convertible had a badly cut forcing cone so I bought the tools from Brownells and gave it a go. It turned out great. I went slow with cutting oil and it is nice and smooth. Here is my question: I didn't go quite as deep as the original cone which I believe gives me a compound angle of 11 transitioning to 5. Logically, this seems good to me, i.e., a steeper angle transitioning to a shallower angle. However, every post on the subject asserts compound angles are bad. I asked Grok (AI) and it stated that many gunsmiths prefer a compound angle. l do understand that a 5 degree angle transitioning to 11 would not be good. So guys, what is the truth here?

 

[s4s4u]

I would say it depends on the transition. A sharp transition could possibly lead to lead buildup. The purpose of the forcing cone is simply to compensate for errors in cylinder alignment, not to swage down a bullet, so it really shouldn't be an issue unless you have significant misalignment of cylinder to barrel where a bullet contacts the transition. I'd say it should be a non-issue, but Murphy can be a MF'er

ETA: If you shoot only jacketed bullets I'd consider it even less of an issue.

 

[41Dude]

I am no help on the angles but I did have a rough forcing cone.
I polished it up using this Lewis lead remover. I replaced the brass discs with some 2000 grit sandpaper and was able to smooth things out to a nice shiny polish. It helped to keep leading at a minimum. Very happy with the result.

PS I did not use the tool in
the barrel. Only used it on the forcing cone to where the rifling starts. Smoothed things out in cone and sharp start of rifling.

 

[contender]

I can't offer direct info about the compound angle from experience.

But,, I will ask a few questions.

Did you shoot some groups as a base line before you worked on the forcing cone?
Did you use a forcing cone depth gauge as you worked on it?
Have you test fired it for groups now?

If so,, did it improve things or not?

 

[XUSNORDIE]

Definitely tracking this thread out of interest.

Also post #4 seems like a logical low risk measure to start with.

 

[Johnnu2]

IMHO, logic would dictate a smooth (i.e. no compound) transition is critical. I have NEVER seen other than a single-angle forcing cone. If it were my gun, I would continue my cut to eliminate the dual angle.

J.

 

[Caballero59]

IMHO, logic would dictate a smooth (i.e. no compound) transition is critical. I have NEVER seen other than a single-angle forcing cone. If it were my gun, I would continue my cut to eliminate the dual angle.

J.

I hear that a lot on the forums, but why? What are the physics that are against a compound angle? In fact, look at it this way. A standard 11 degree forcing cone amounts to a compound angle with the first angle of 11 deg and the second of 0 deg. But I get it...a reverse compound of a 5 deg followed by an 11 deg would be a no-go.

 

[Dan in MI]

I’m with Contender. The proofs in the groups. Even without a “pre” the after groups need to be good. If they aren’t then I’d start looking for other answers.

 

[NikA]

I hear that a lot on the forums, but why? What are the physics that are against a compound angle? In fact, look at it this way. A standard 11 degree forcing cone amounts to a compound angle with the first angle of 11 deg and the second of 0 deg. But I get it...a reverse compound of a 5 deg followed by an 11 deg would be a no-go.

Every transition is a point where metal from the bullet is forced to further deform and could get deposited on a rough surface. At a minimum I would lap a two-angle cone to make sure the cut transition was absolutely smooth. I doubt there are any benefits to a multi-angle cone.