Forcing Cone Angle

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  • Last Post 08 June 2022
Aaron posted this 04 June 2022

I admit, I am stymied. Having cut at least 6 forcing cones with a 11 degree cutter, I am mystified why this forcing cone will not cut. When placing the cutter into the forcing cone, it seats fine to a proper depth for cutting - or so it seems. The cutter just spins however with no cutting or bite whatsoever.

The cutter is a Brownells 11 degree chamfer cutter and is sharp as all get out. I have cut the 45 caliber cones but the 38/357 cones will not be cut. For the life of me I can't visualize this in my minds eye. The 11 degree blade should be impacting the factory lip and cutting - unless the factory angle (Pietta Alchimista III) is greater than 11 degrees.

The reason I am cutting this cone will become obvious when you see the images of the cone below. To say I am not happy with this is an understatement. This is the quality that is getting sold for upwards of $700 on these particular revolvers? Fortunately I did not pay that kind of money for this one when I purchased it.

So....any tips on why the silly 11 degree forcing cone cutter will NOT cut?

It's sharp. I am turning it the correct way. It is fully seated. The bushing is in place. yada yada yada

With rifle in hand, I confidently go forth into the darkness.

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TRKakaCatWhisperer posted this 04 June 2022

Hmmmm.  Is it engaged deeply enough to touch the cone?  Or is it just sliding?

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Aaron posted this 04 June 2022

If I were a betting man, I would say the very tip of the tool is catching on the bore at a barrel crush point and just a few thousands of an inch before the tool engages the cone with the blade. I could see the rifling getting polished down there. It just spins and is definitely NOT touching the cone face. There is ever-so-slight wiggle. To the eye, it seems seated and far enough into the cone to work.

You can see from the images, it is not cutting at the forcing cone face or anywhere else for the matter.

With rifle in hand, I confidently go forth into the darkness.

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Glenn R. Latham posted this 05 June 2022

I've only cut a couple forcing cones so I'm not much help.  Best guess would be to remove the cutter from the rod and see how it fits.  Maybe ink everything up and get a better view of what it's stopping against.  But you've probably already tried this.

Glenn

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Aaron posted this 05 June 2022

I've only cut a couple forcing cones so I'm not much help.  Best guess would be to remove the cutter from the rod and see how it fits.  Maybe ink everything up and get a better view of what it's stopping against.  But you've probably already tried this.

Glenn

   It is inserting into the cone to 1/4 its length. It is just not making contact at the blade/cone interface. It spins freely. It seems to be getting stopped just prior to the blade/cone contact and the lands show polishing where the cutter is hitting the lands down in there. I think the barrel has been crushed by the frame preventing full insertion and preventing the blade surface from making contact.

With rifle in hand, I confidently go forth into the darkness.

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Aaron posted this 05 June 2022

To provide a visual.

Here is a short video of the 11 degree cutting tool inserted and rotating in the correct direction to cut the cone - which it is not.

https://www.youtube.com/shorts/M1t0EuXf_SA

 The tool tip measures out at .310" and inserts not only into the forcing cone, but the muzzle as well. When inserted into the muzzle, it bites the rifling like it should be in the breech but doesn't.

A couple of photos:

This is how far it inserts into the muzzle. The tool is the correct size tool. 38-45 Caliber.

And inserted into the forcing cone

The rascal just spins! It will not cut. It does not seem to be touching the forcing cone anywhere. Yes it is sharp.

 

With rifle in hand, I confidently go forth into the darkness.

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Clod Hopper posted this 05 June 2022

An Eleven degree cutter is not always the best angle and can make things worse.  Try an 18 degree cutter.  Call Brownells.  I do not see how you can remove that much metal and still have a good throat.  If the funnel is too long, the bullets loses support when fired and gets crocked.  If it shoots okay, I would leave it alone.

Dale M. Lock

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David Reiss posted this 05 June 2022

I am not a physicist, but have heard of hydrogen embrittlement during some plating processes. I also know that hydrogen is part of the hot gas created in smokeless powder combustion. So my question is, can this happen to forcing cones? Is this the issue here? Never heard of it happening, but that is a really badly damaged forcing cone. Hopefully someone with a background can address this theory. I know I am probably wrong, but it makes me wonder. 

Last it may be time for a barrel replacement because it is hard to determine how deep that erosion goes. 

David Reiss - NRA Life Member & PSC Range Member Retired Police Firearms Instructor/Armorer
-Services: Wars Fought, Uprisings Quelled, Bars Emptied, Revolutions Started, Tigers Tamed, Assassinations Plotted, Women Seduced, Governments Run, Gun Appraisals, Lost Treasure Found.
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Aaron posted this 05 June 2022

I am not a physicist, but have heard of hydrogen embrittlement during some plating processes. I also know that hydrogen is part of the hot gas created in smokeless powder combustion. So my question is, can this happen to forcing cones? Is this the issue here? Never heard of it happening, but that is a really badly damaged forcing cone. Hopefully someone with a background can address this theory. I know I am probably wrong, but it makes me wonder. 

Last it may be time for a barrel replacement because it is hard to determine how deep that erosion goes. 

Very interesting theory David. This revolver has not had more than 50 rounds through it however and never a jacketed bullet. I originally thought the mess at the forcing cone was an occlusion which I have had in barrels and on the brass frames of several Italian imports. Careful inspection of the forcing cone reveals a pattern which can sort of be seen in the images here. They are low resolution images but if you study them, you can see the pattern.

This looks to be a tool mark like chatter. It looks like debris was not removed when cutting the cone and that debris caused the bit to chatter. This is the worst forcing cone seen on an Italian import. Most clean right up but for some reason, this rascal, which has already been sent back for repair once, is just going to fight me even more. If I showed you the photo of the original hammer cam, you would not believe it. For a gun made in 2016, this one defied belief. Italy responded that they had some major turn-over at the factory and a lot of new "talent" had access to tools to the detriment of the brand.

So....while this looks like erosion on the surface, it's actually tooling. I was hoping to get rid of it with a 11 degree chamfer tool but can't get that tool to bite. Shucks.

I do like the sound of Hydrogen Embrittling however.

With rifle in hand, I confidently go forth into the darkness.

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TRKakaCatWhisperer posted this 05 June 2022

OK.  use a magic marker or dykem blue (layout fluid used by machinists)

this will tell you WHERE the point(s) of contact are.

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Boschloper posted this 06 June 2022

What is the cutter made from and what is the finish on the barrel?

If the barrel finish is the nitriding process commonly known as QPQ or FNC it is too hard to cut with a tool steel cutter.  You have to use carbide, and even then tool life will be short.

FNC is harder than woodpecker lips.

 

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Ken Campbell Iowa posted this 06 June 2022

a simple test for hardness is to buy a small ( swiss ) file at Ace hardware and see if it " bites " on the cone area ...  if it doesn't bite ( you don't have to file a groove, just the feel is sufficient ) ... it is " file hard " and your HSS cutter will not work as is.  if the file grabs, there is a geometry problem with your cutter/cone.  some nail polish/dykem will give you some clues.

those tool marks are usually from the factory running in the cone cutter too far too soon and not clearing the chips ... the cutter grooves overflow with work hardened chips and these gouge out those grooves ...

worst case, a gunsmith can remove the barrel and cut or grind the cone in a lathe ... i am not a pistolsmith so i don't know how much you can clean up the gouges and retain accuracy ...  ?? set it back 2 threads and cut a fresh better cone ?? 

i bet most of us have had at least one of these " dammit " guns ... you are not alone ( heh ) ...

ken

 

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Aaron posted this 06 June 2022

Off to get some Dykem. Seems a geometry issue to me but you never know. I'll try to establish the hardness of the barrel as well. I seem to recall reading somewhere how these barrels are made. It was a comparative study of the imports.

With rifle in hand, I confidently go forth into the darkness.

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358156hp posted this 08 June 2022

It sounds like you need to first identify what angle your forcing cone is cut to. You also may be dealing with something that has been modified, or has the forcing cone cut to some sort of compound angle. I have an 11 degree, and an 18 degree set, but there are others out there. It could also be a factory screw up that got "fixed" before shipment.

https://www.brownells.com/gunsmith-tools-supplies/handgun-tools/barrel-tools/chamfering-tools/barrel-chamfering-plug-gauges-prod626.aspx

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OU812 posted this 08 June 2022

I've throated two revolvers using a 11 degree cutter. One was a stainless 686 and the other was a blued Blackhawk 45 long Colt. The stainless 686 was easy to recut, but the blued Ruger took lots more pressure on cutter to achieve cut. I also thought the cutter was defective, but the blued barrel steel just needed more force to cut. Try using more force on cutter.

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OU812 posted this 08 June 2022

Why are you wanting to reduce forcing cone angle? Maybe to reduce leading in this area? The cylinder face and throat area will always lead some when shooting lead bullets. Try shooting powder coated bullets to eliminate leading

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