peterg
.240 Incinerator
Posts: 6 
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Post by peterg on Dec 9, 2014 12:04:25 GMT -5
Hi there. I'm trying to learn what makes good revolvers shoot well.
I have repeatedly run across folks writing of cutting forcing cone angles at 11 degrees.
I'm curious what makes 11 degrees the optimal angle. Why not 10 degrees or 12 degrees or some other angle?
Please understand I am not questioning the wisdom of cutting forcing cones at that angle or suggesting that another angle is better. I am just trying to learn how that came to be the angle of choice for cutting forcing cones. Has 150+ years of revolver history simply shown that to be the best angle, or is it based on some theoretically perfect angle, or is it because it was because it might have derived from bisecting a common 45-degree angle twice (which gives 11.25 degrees)? Perhaps it is to stump folks like me. Regardless, I cannot find the answer to this anywhere.
Again, I'm not trying to challenge anyone or any accepted wisdom or technique, because I don't know squat. I'm just trying to learn.
Thanks in advance for any information about this.
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Post by bradshaw on Dec 9, 2014 13:41:34 GMT -5
peterg.... why not question so-called wisdom of re-cutting a forcing cone? And your division of 45-degrees twice to arrive at 11-degrees may have some validity as an easily workable angle in machine tools of the 1800's. Curious possibility.
What makes a revolver shoot?
* uniform bore with firm groove-diameter rifling.
* relatively firm chamber exits (throats).
* Relatively straight chamber-to-bore alignment.
Details which affect shooter ability to utilize intrinsic accuracy include trigger pull, lock time, grip sights, and ammunition. (this is another discussion.)
Back to the forcing cone. Job of a forcing cone is to facilitate the bullet's passage from cylinder into barrel on as straight a path as possible without distorting bullet.
* Forcing cone must be wide enough at the barrel mouth to not shave bullet.
* Forcing cone must be smooth enough to not abrade bullet.
* Forcing cone must be gradual enough to not hammer bullet.
* Forcing cone should be short enough to guide shoulder of bullet into rifling----while chamber supports heal.
Sometimes it seems a manufacturer cuts the forcing cone as an afterthought, cutting the cone off bore axis, or rough as a cob. To properly correct such an abomination, the cone must be dressed or cut on the bore axis. A lathe is the safest method. A hand-held reamer may just follow the off-center or off-axis original.
Many thousands of revolvers have overly-deep, rough, or cockeyed forcing cones. Correcting such a bastard cone is necessary to pursue accuracy. Avoid a cure which amplifies the disease. Generally, the forcing is cut with an angle of 5 to 11 degrees. Both angles, along with angles in between, have been used for years, starting years before gun writers ever heard of a forcing cone.
ACCURACY must be the arbiter of work done on a revolver. Accuracy may be glimpsed at 25 yards, seen at 50 yards, but it takes 100 yards to begin to know accuracy. testing at 7, 10, or 15 yards is total bullroar.
David Bradshaw
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Post by Lee Martin on Dec 9, 2014 19:28:31 GMT -5
I can't add much to David's response. That's about as dead-on correct as you'll get. To echo his comments, there are four things we strive for in a forcing cone: 1) Centered on the bore 2) Concentric 3) Short 4) Smooth / polished We typically cut elevens, but if you have the aforesaid, the angle is less critical (assuming it's a reasonable transition, say 5 to 12 degrees). Here's one of ours on a 0.512" blank: Centering the bore off the grooves, not the lands:  Boring bar set to eleven degrees:  Cut and polished 11 degree cone. Notice the length?  -Lee www.singleactions.com"Building carpal tunnel one round at a time" |
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Post by contender on Dec 10, 2014 10:50:18 GMT -5
Excellent info David & Lee!
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klnc
.30 Stingray
Posts: 111
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Post by klnc on Dec 10, 2014 12:15:27 GMT -5
What I've never understood is why manufacturers don't just cut the cone at the optimum angle to begin with? It shouldn't be hard to set it up at the beginning--why does it have to be done on a custom basis afterward?
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Post by bradshaw on Dec 10, 2014 14:36:54 GMT -5
kinc.... to answer your question requires a look at recent history. First off, major industry players have a grasp of "optimum angle." Unfortunately, industry lost sight of, around 1980, the importance of alignment, depth, and finish of the forcing cone. To accommodate lapses in quality control, which includes chamber-to-bore alignment, the forcing cone was widened. To widen the cut, the cone was cut deeper.
This was a period of exploding participation in magnum revolver shooting. Handgun silhouette, hunting, big powerful handguns. Some revolvers were blown up, mostly by persons not involved in disciplined marksmanship. Poorly fitted and out-of-time revolvers contributed to spitting, the shaving of bullet out the cylinder/barrel gap. Rather than tighten up quality control, an expedient was found----enlarge the forcing cone.
Far as I know, and it is part of the written record, it is this shooter who raised the red flag to Smith & Wesson and Sturm, Ruger, and a few other manufacturers. Unlike the others, Dan Wesson never veered from a short, smooth cone.
Quality control requires a positive attitude, a state of mind.
David Bradshaw
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peterg
.240 Incinerator
Posts: 6
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Post by peterg on Dec 12, 2014 20:17:00 GMT -5
I've been away a few days and just now saw all this. This is helpful stuff. Many thanks.
Lee, I don't know why I was thinking that a forcing cone would be much longer than the cut one you show. Thanks for taking the time to post those pics. They really can save a lot of words.
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Dec 12, 2014 21:21:23 GMT -5
Weird. I commonly see factory forcing cones that appear to be a quarter inch long or better. I have a S&W M64 beside me with a forcing cone length approaching 3/8 inch or better. It's also as rough as a cob.
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Post by boxhead on Dec 13, 2014 0:16:11 GMT -5
Weird. I commonly see factory forcing cones that appear to be a quarter inch long or better. I have a S&W M64 beside me with a forcing cone length approaching 3/8 inch or better. It's also as rough as a cob. How does it shoot? |
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edk
.375 Atomic
Posts: 1,118
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Post by edk on Dec 20, 2014 13:12:52 GMT -5
If a 38/.357 revolver had a cylinder with perfect lockup/alignment and a 3/8" long 11* forcing cone, it would be capable of digesting a 50 cal bullet. Think about it!
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Post by olgeorge on Dec 20, 2014 14:06:44 GMT -5
Before ordering a forcing cone reamer set from Brownell's several years ago, I called Ron Power for his advise. To the best of my recollection, he said the angle wasn't as important as being smooth and concentric and not too large in diameter. Brownell's claimed 11 degrees is best. They have a gage to check the size of the cone. L. O. G.
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Post by bradshaw on Dec 21, 2014 7:56:18 GMT -5
358156hp.... as boxhead asks, how does it shoot? A deep, rough cone, as you describe, is not cause for cheer. Vintage Smith & Wessons are notable for short, smooth cones. In the early 1980's things got out of hand, as magnum revolvers proliferated and a new generation subjected them to volume firing, the disciplined side of this consumption on the firing lines of IHMSA handgun silhouette. Persons lacking the accuracy imperative, yet enamored of magnum loads----read rocks & dynamite----threw their sixguns loose and out of time. An out-of-time revolver, or one with the forcing cone eroded, spits. Factories found a quick, cheap "cure" for spitting by hogging out the forcing cone. This braindead approach became a curse on accuracy. Although it has abated somewhat, sloppy forcing cone disease continues to this day.
The proper remedy is to pull the barrel, set back the barrel shoulder on a lathe. The barrel is set back enough to clean up the cone when the stub is trimmed, while timing barrel threads so that the barrel hand-tightens to 10-degrees Before Top Dead Center.
(Note that premature thread timing results in over-tightening of the barrel and a compression ring in bore.)
Ron Power knows his dope on revolvers, and we are in accord on the importance of the forcing cone to accuracy. Along with Lee Martin, who joins in singing the importance of this detail.
David Bradshaw
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Post by tek4260 on Dec 22, 2014 11:08:43 GMT -5
So where does this leave the proponents of Taylor and Maxi Throating. They proclaim it superior....
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Post by bradshaw on Dec 22, 2014 11:56:42 GMT -5
tek4260.... to start, we must define our terms.
Freebore in a revolver----a straight, bullet diameter, unrifled distance between barrel face and rifling. Length of freebore may vary. I will take freebore with a short forcing cone over any long-taper forcing cone any day.
Now, we need definitions for Taylor Throating and Maxi-Throating.
David Bradshaw
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Post by Markbo on Jan 18, 2015 22:36:09 GMT -5
As usual this type of conversation brings up more questions for me. Lee, since you mentiond it why measure off the grooves and not the lands? What does that gain you? 2nd you and David both mention... why a short forcing cone...wouldnt a longer transition make any correction smoother??
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