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Old 08-22-2009, 11:57 AM
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Default forcing cone

I see reference to forcing cones quite a few times here. What is the forcing cone in a revolver. Do automatics have them? I had a squib last week and when I pushed the bullet back toward the cylinder, it got noticeably harder to push at the very end. Thanks for the information.
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Old 08-22-2009, 12:22 PM
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A forcing cone is the tapered beginning of the lands at the origin of the rifling of a gun barrel,The forcing cone allows the projectile to be gradually engaged by the rifling, thereby centering the projectile in the bore. All guns have some type of forcing cone.

Ken
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Old 08-22-2009, 03:31 PM
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Quote:
Originally Posted by Aussie44 View Post
All guns have some type of forcing cone.

Ken
Wouldn't pistols (a handgun in which the next round to be fired is located in the barrell) and rifles have a "throat" instead of a "forcing cone" as in revolvers?
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Old 08-22-2009, 08:08 PM
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The forcing cone is a revolver "thing".

The forcing cone is the funnel-like mouth at the rear of a revolver barrel.

Its more important and complicated than many people think.
Its not "just a funnel", its a critical feature that's cut with precision tools and must be properly gaged with a special drop-in gage to insure its within a narrow specification.
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Old 08-22-2009, 10:00 PM
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[QUOTE=dfariswheel;1065399]The forcing cone is a revolver "thing".[UOTE]

No it isn't.
Shotguns have a forcing cone.Rifles and Auto pistols have a throat to ease the bullets entry into the rifling which is no different than a forcing cone.The only difference with a revolver is the jump from the cylinder to the barrel which is why they have a 9 1/2,11 and a 18 degree entry angle.

Ken
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Old 08-23-2009, 11:37 AM
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Was it the forcing cone that made it harder to push my squib out of the barrel? It doesn't sound like it should have if the cone is largest closest to the cylinder.
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Old 08-23-2009, 11:45 AM
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Originally Posted by lucky7 View Post
Was it the forcing cone that made it harder to push my squib out of the barrel? It doesn't sound like it should have if the cone is largest closest to the cylinder.
If you are shooting lead bullets and there is lead fouling in that part of the barrel (very common), you will notice more resistance there.

Also, The bore tends to be tighter where the barrel screws into the frame. The process of torquing the barrel causes a slight constriction there. The harder the barrel is torqued on, the tighter the constriction. How far did the bullet make it into the barrel and what kind of bullet?

Last edited by aphelion; 08-23-2009 at 11:50 AM.
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Old 08-23-2009, 11:46 AM
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Sounds like you have a rough forcing cone or a tight area under the barrel threads,And maybe what is stated above.

Ken
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Old 08-23-2009, 12:37 PM
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Is there an optimum angle of forcing cone by each specific caliber or would it be the same for many calibers?
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Old 08-23-2009, 12:48 PM
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Quote:
Originally Posted by aphelion View Post
Also, The bore tends to be tighter where the barrel screws into the frame. The process of torquing the barrel causes a slight constriction there. The harder the barrel is torqued on, the tighter the constriction.
Barrel threads are straight threads, not tapered pipe threads. If the frame and barrel have been properly threaded, there shouldn't be any reduction in bore diameter worth worrying about at the torque levels used in barreling revolvers.

Optimum forcing cone angles depend upon bullet material (jacketed or lead) and length of the bullet. Most of us can't tell the difference between any of the commonly used forcing cone angles.

Last edited by WR Moore; 08-23-2009 at 12:50 PM.
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Old 08-23-2009, 03:18 PM
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Quote:
Originally Posted by WR Moore View Post
Barrel threads are straight threads, not tapered pipe threads. If the frame and barrel have been properly threaded, there shouldn't be any reduction in bore diameter worth worrying about at the torque levels used in barreling revolvers.
In a perfect world that's true. In our world barrels tend to be a crush fit in the frame all too often with a corresponding tight area in the barrel. Ruger is the worst but you see it in S&W's too. I've had 2 new S&W's with the barrel torqued so tight you could see a jog in the rifleing at the barrel/frame face from the barrel actually being twisted.
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Old 08-23-2009, 03:23 PM
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Quote:
Originally Posted by tomcatt51 View Post
In a perfect world that's true. In our world barrels tend to be a crush fit in the frame all too often with a corresponding tight area in the barrel. Ruger is the worst but you see it in S&W's too. I've had 2 new S&W's with the barrel torqued so tight you could see a jog in the rifleing at the barrel/frame face from the barrel actually being twisted.
Amen, I've seen this too!
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Old 08-23-2009, 07:24 PM
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A constricted bore in the thread area is known as "pressure dimpling" or "pressure compression".

If the barrel is torqued in too tight, the pressure causes the area to compress, leaving a tight spot in the rear of the revolver barrel.
S&W had a real problem with this when they first went from pinned barrels to torqued barrels.
The pinned barrels weren't torqued in that tight since they had a pin to prevent it unscrewing.
The new non-pinned barrels required torquing much tighter, and S&W had some trouble with over-torqued barrels with pressure compression tight spots.
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Old 08-25-2009, 12:07 AM
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Quote:
Originally Posted by WR Moore View Post
Barrel threads are straight threads, not tapered pipe threads. If the frame and barrel have been properly threaded, there shouldn't be any reduction in bore diameter worth worrying about at the torque levels used in barreling revolvers.
Actually what you are saying is not quite correct. Of course they are not pipe threads, but there will still be some constriction. Back in my silhouette days, I saw a lot of Dan Wessons with constricted bores on both ends of the barrel, at the frame and at the barrel nut. A lot of people attempted to deal with this by lapping. The constriction is not a lot, but it is there. It can be felt when pushing a soft lead slug through the bore.

Last edited by aphelion; 08-25-2009 at 12:20 AM.
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Old 09-05-2009, 10:34 AM
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Default forcing cone

aphelion:
The darn thing was so far out the barrel on a 4" Model 19 that it was flush with the end of the barrel. If it had been out any farther it would have been sticking out of the barrel of the gun, and may not have had to push it all the way back through.

Last edited by lucky7; 09-05-2009 at 10:35 AM. Reason: spelling
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