Revolver forcing cones

[M. De Land]

I thought this topic might be of interest to others as well as myself having had some experience with them in center fire and percussion guns.
While tuning up my Pietta 58 Rem (Remington New Model Army) I think is the ten dollar title, I learned some things about forcing cone geometry that may be interesting to relate.
I deciding to make a frame spud to hold a chucking reamer so as to make all the chamber mouths the same diameter and depth (.450). After satisfactorily accomplishing this I wanted to clear the tight spot under the frame threads in the barrel by fire lapping it out. Almost all factory revolvers will show some constriction in the barrel bore under the frame threads which is not conducive to top accuracy and often promotes bore leading.
Fire lapping is the practice of first measuring your bore diameter and making up some conical slugs which are rolled in mild abrasive and shot down the bore with a minimum charge to just clear the barrel.
I had used this process before in center fire guns with good success so decide to experiment with my Pietta I was over hauling.
Well to make a long story short the fire lapping slugs so altered the forcing cone that accuracy that should have been enhanced with the line reaming was dismal however it did relieve the tight bore under the frame threads.
I could see the cone had changed dramatically from the fire lapping so I put it in the lathe and cut it back one thread so as to have enough fresh metal in the bore to re-cut the cone.
I used the 11 degree cutter as it had worked so well in my center fire revolvers cutting the fresh cone just enough so that a ball would seat half it's diameter in the new cone.
Accuracy was restored instantly and the Pietta is now more accurate than my factory Ruger Old Army. I wish now I had used the 7 degree cone cutter first as if it didn't work I could always use the 11 degree later to lengthen it. My hunch is the steeper angle may be a bit better for ball shooting.
I should point out that when one is talking of throat or cone angle we are talking included angle, that is in a 7 degree cone each side will have a taper of 3.5 degrees for a total of 7 degrees.

 

[William P Sepessy]

Glad to hear the 11 degree forcing cone cutter worked out. I have heard arguments both for and against using this on a cap & ball pistol intended for round balls. I never understood the explanation why this treatment would be so effective(usually) on cartridge guns but not so for round ball. Just curious what projectile you used for the testing.

 

[M. De Land]

Ball mostly but it seems to work with bullets too. I don't know what they use in the ROA cone, I've never made a cast of my ROA and measured it.

 

[rickystl]

On my 1860 Army, I had a trigger job, taller front sight, and an 11 degree cut on the forcing cone. hard to believe how much better it shot. Really improved the accuracy. Shoots right where you point it. Seems that there is less deformation of the ball while entering the cone.
The late Tom Ball swore by the 11 degree cut. He said they would do it even to the early replica Peacemakers.

Rick

 

[M. De Land]

Glad to hear the 11 degree forcing cone cutter worked out. I have heard arguments both for and against using this on a cap & ball pistol intended for round balls. I never understood the explanation why this treatment would be so effective(usually) on cartridge guns but not so for round ball. Just curious what projectile you used for the testing.

The reason I think a 7 degree cone may be better than a 11 degree cone for ball shooting is because a ball is so short compared to a bullet and the quicker it takes the rifling to seal the bore the better. Mine is cut to 11 degrees and shoots better than my factory ROA so I can't complain but am curious about the 7 degree cone not having tried one. I have the tools for cutting either.

 

[hawkeye2]

On my 1860 Army, I had a trigger job, taller front sight, and an 11 degree cut on the forcing cone. hard to believe how much better it shot. Really improved the accuracy. Shoots right where you point it. Seems that there is less deformation of the ball while entering the cone.
The late Tom Ball swore by the 11 degree cut. He said they would do it even to the early replica Peacemakers.

Rick

I have a R&S that Tom did a complete accuracy job on and I just bought a friend's Tom Ball Remington and got the original test target Tom shot with it. 25 yards, Ranson rest, 20 grains 3f, filler, 6 shots 1 from each chamber, one ragged hole. That's with an 11 degree forcing cone in one of his barrels. Tom advocated the 11 degree cone and used it in all his guns and would cut a cone for anyone who stopped at his booth for a few dollars. I've followed his lead and cut 11 degree cones in my revolvers as the factory Italian cones are usually steep and rough. There are a lot of arguments for different angles between 5 and 11 degrees but the biggest reason to recut the cone is to get a concentric and smooth lead into the rifling. The only true test is to cut and shoot but if your gun shoots its best group with a 7 degree cone and you have cut an 11 in testing there is no going back. BTW a cone shoud never be cut with compound angles, example a 5 leading into an 11.

M. De Land, like you I have tooling to cut a 7 degree cone but have never tried it. Mike Brackett, Goons Gun Works, likes the 7 degree cone arguing that the ball has a shorter distance to travel before engageing the rifling and Its possible he has a valid argument. I think I'll stick with what I've been doing all along. Beyond guiding the projectile into the bore without deforming it or allowing to bounce around in the cone its other function is to compensate for misalignment of the chambers with the bore and it's possible any reasonable angle will do that well.

 

[M. De Land]

I have a R&S that Tom did a complete accuracy job on and I just bought a friend's Tom Ball Remington and got the original test target Tom shot with it. 25 yards, Ranson rest, 20 grains 3f, filler, 6 shots 1 from each chamber, one ragged hole. That's with an 11 degree forcing cone in one of his barrels. Tom advocated the 11 degree cone and used it in all his guns and would cut a cone for anyone who stopped at his booth for a few dollars. I've followed his lead and cut 11 degree cones in my revolvers as the factory Italian cones are usually steep and rough. There are a lot of arguments for different angles between 5 and 11 degrees but the biggest reason to recut the cone is to get a concentric and smooth lead into the rifling. The only true test is to cut and shoot but if your gun shoots its best group with a 7 degree cone and you have cut an 11 in testing there is no going back. BTW a cone shoud never be cut with compound angles, example a 5 leading into an 11.

M. De Land, like you I have tooling to cut a 7 degree cone but have never tried it. Mike Brackett, Goons Gun Works, likes the 7 degree cone arguing that the ball has a shorter distance to travel before engageing the rifling and Its possible he has a valid argument. I think I'll stick with what I've been doing all along. Beyond guiding the projectile into the bore without deforming it or allowing to bounce around in the cone its other function is to compensate for misalignment of the chambers with the bore and it's possible any reasonable angle will do that well.

The other thing I have found with my plug gauges in most all revolvers is bore tightness just ahead of the forcing cone from the frame threads when the barrel is put in compression against the barrel shoulder and frame seat. The reason is from the V threads that are lubed and as they tighten they compress the barrel radially from tremendous mechanical cam angling.
V threads are great for self centering and carrying load but I think a square thread would be better suited for revolver barrels so as not to compression choke them at the front end.
This is where a good lead slug hand lap job, with the barrel in the frame, is a good idea.
I fire lapped one that worked well but screwed up the factory forcing cone. I had to re-cut the cone but the factory cone was so steep that the 11 degree cutter got into clean metal so no set back was required. I thought I had set the barrel back but was confusing it with another gun. That is when I used the 11 degree cutter.
True, you do not want a double taper angle in the cone and if you set back one thread you have to change the loading lever barrel purchase which is certainly doable but a pain in the keester.