11 degree cone
- Thread starter Kanook
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Jimbo357mag
Hawkeye
I don't shoot much lead but from what I have heard here is one vote for the 11 degree forcing cone.
Maybe some others will chime in.
Maybe some others will chime in.
It's supposed to spit less and shootbetter. I assume the bullet wobble, before it engages the rifling, is more gradual/less abrupt than the steeper 18 degree cone.
www.GrantCunningham.com has some info on this procedure. Sounds like a specialty reamer, may be cost prohibited.
David Bradshaw
Blackhawk
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The 11-degree included angle forcing cone is an industry standard. I have not heard of a standard on how deep vis-a-vis caliber the cone is to be cut. I consider the forcing cone to be the most misunderstood, opinion-laden dimension in revolver building.
If you proceed from the position that the FORCING CONE is a NECESSARY EVIL, you will incorporate the least amount that seats the bullet in the barrel without shaving.
A revolver wants each chamber in the cylinder to lockup on-axis with the barrel, with exit holes firm enough to just let the bullet slip through. Conceptually, it is a miracle some revolvers shoot as well as they do. Counting on the bullet to align the chamber with the barrel puts stress on the bullet, which, in the jargon of manufacturers, obturates----distorts----the bullet. Much obturation theory precedes from the lead Minie ball of Civil War fame, where obturation was a good thing. The Minie bullet was made undersize for loading in fouled caplock rifles; gas pressure swelled the skirt of the hollow-base bullet against the rifling.
Manufacturers have on and off dealt with loose tolerances by opening the forcing cone, a GUARANTEED ACCURACY KILLER. Gunsmiths for whom accuracy is an abstraction have been guilty of the same reactionary technique of hogging out the forcing cone.
I prefer a revolver which allows the bullet shoulder to meet the rifling while the chamber exit holds the bullet heal. I have one exception: groove diameter freebore, which introduces the bullet to the rifling concentric to the bore.
Building an accurate revolver is not about loosening tolerances; it is about tightening them.
David Bradshaw
If you proceed from the position that the FORCING CONE is a NECESSARY EVIL, you will incorporate the least amount that seats the bullet in the barrel without shaving.
A revolver wants each chamber in the cylinder to lockup on-axis with the barrel, with exit holes firm enough to just let the bullet slip through. Conceptually, it is a miracle some revolvers shoot as well as they do. Counting on the bullet to align the chamber with the barrel puts stress on the bullet, which, in the jargon of manufacturers, obturates----distorts----the bullet. Much obturation theory precedes from the lead Minie ball of Civil War fame, where obturation was a good thing. The Minie bullet was made undersize for loading in fouled caplock rifles; gas pressure swelled the skirt of the hollow-base bullet against the rifling.
Manufacturers have on and off dealt with loose tolerances by opening the forcing cone, a GUARANTEED ACCURACY KILLER. Gunsmiths for whom accuracy is an abstraction have been guilty of the same reactionary technique of hogging out the forcing cone.
I prefer a revolver which allows the bullet shoulder to meet the rifling while the chamber exit holds the bullet heal. I have one exception: groove diameter freebore, which introduces the bullet to the rifling concentric to the bore.
Building an accurate revolver is not about loosening tolerances; it is about tightening them.
David Bradshaw
tek4260
Buckeye
Kanook said:
I did several of mine back when I had a reamer. It is supposed to be better because it is a more gradual taper into the barrel than the factory cone. Now, unless your revolver is seriously misaligned you "probably" won't see any improvement in accuracy unless you are a much better shot than me. You should see less leading, as was the case with my Uberti.
With all that said, I'd do it. I still believe there is peace of mind in knowing your revolver is "right"
As I recall, the "11 degree forcing cone" came from experiences gained while shooting low-speed lead wadcutter bullets out of .38 cal competition revolvers.
Picturing the shape and length of a .38 LWC bullet....one can imagine the variables involved with attempting to optomise a given forcing cone for any one of a wide variety of bullet designs and calibers.
I suspect that this aint a one size fits all situation, so my thoughts has always been...how does the gun shoot as-is?.....and...If it aint broke, don't fix it.
DGW
Picturing the shape and length of a .38 LWC bullet....one can imagine the variables involved with attempting to optomise a given forcing cone for any one of a wide variety of bullet designs and calibers.
I suspect that this aint a one size fits all situation, so my thoughts has always been...how does the gun shoot as-is?.....and...If it aint broke, don't fix it.
DGW
Brownells has a tool to ream the forcing cone wile the barrel is still in the frame.
edlmann
Blackhawk
Kanook said:
What gun?
David Bradshaw
Blackhawk
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Kanook... rereading your original post, it looks like you're about to install an aftermarket barrel, which you will turn and thread and set the gap on. And you wonder whether to cut an 11-degree (included angle) cone. Versus what, a 5-degree cone? An 11-degree cone with freebore?
Whichever forcing you cut, do it on a lathe and keep it as shallow as possible, 1/4", maybe 3/8". Less, if chamber-to-bore runout doesn't exceed .003".
If you are about to install a factory barrel, the barrel should hand tighten to 10-degrees or so before Top Dead Center. If you hand tighten to 30-degrees before TDC, tightening it to INDEX will form a crush ring in the bore (where barrel butts frame).
For whatever reason, THREAD TIMING has been a production problem for years at Ruger and, to some extent, at S&W.
And if your idea is to correct an off-axis forcing cone by hand grinding or reaming over it, I think the reamer will just follow the old cone.
Too many forcing cones are:
a) too deep.
b) rough.
c) off axis.
d) any or all of the above.
Please do not take these notes----which concern a few things to be aware of----as a How To.
David Bradshaw
Whichever forcing you cut, do it on a lathe and keep it as shallow as possible, 1/4", maybe 3/8". Less, if chamber-to-bore runout doesn't exceed .003".
If you are about to install a factory barrel, the barrel should hand tighten to 10-degrees or so before Top Dead Center. If you hand tighten to 30-degrees before TDC, tightening it to INDEX will form a crush ring in the bore (where barrel butts frame).
For whatever reason, THREAD TIMING has been a production problem for years at Ruger and, to some extent, at S&W.
And if your idea is to correct an off-axis forcing cone by hand grinding or reaming over it, I think the reamer will just follow the old cone.
Too many forcing cones are:
a) too deep.
b) rough.
c) off axis.
d) any or all of the above.
Please do not take these notes----which concern a few things to be aware of----as a How To.
David Bradshaw
I will be installing a 10 1/2 357max barrel on one of my three screws. I have everything I need ;;;;formy build now. Just gotta wait till my bicep finishes healing to do the the swap though and figured if I should want sometbing dicferent done now is tbe time. Thanks again for all the input.
bigboredad
Blackhawk
how did you get a 11 degree cone from the factory?kelbro said:
mrbumps
Blackhawk
bigboredad said:
All my 45 Colts have 11 degree cones from the factory too. I puchased a gauge to measure them from Brownells because I was going to cut mine to 11 degrees, but they already were!
David Bradshaw
Blackhawk
- Joined
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- Messages
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I imagine that within a certain latitude----and I don't know what it is----a revolver bullet doesn't care what degree of "included angle" a forcing cone is. A bullet likes the smoothest transition from chamber to barrel possible. A bullet wants its heal supported by the chamber as its shoulder meets the rifling----unless there is freebore to hold the bullet concentric to the bore as it meets the rifling.
A wide angle forcing cone does violence to the bullet. The same is true of an abrupt leade in a rifle barrel.
I don't think there is anything magical about an 11-degree cone, other than it has helped to produce great accuracy for generations. The very slow angle so good for rifle accuracy presents a dilemma in a revolver: how deep to insure the bullet stays inside the cone when chamber alignment is off? Manufacturers want the cone to accommodate whatever misalignment their specifications allow.
A big forcing cone does not bring back accuracy that chamber misalignment throws away.
If I had to describe a good forcing cone in three words it would be, CONCENTRIC, SMOOTH, MINIMAL.
David Bradshaw
A wide angle forcing cone does violence to the bullet. The same is true of an abrupt leade in a rifle barrel.
I don't think there is anything magical about an 11-degree cone, other than it has helped to produce great accuracy for generations. The very slow angle so good for rifle accuracy presents a dilemma in a revolver: how deep to insure the bullet stays inside the cone when chamber alignment is off? Manufacturers want the cone to accommodate whatever misalignment their specifications allow.
A big forcing cone does not bring back accuracy that chamber misalignment throws away.
If I had to describe a good forcing cone in three words it would be, CONCENTRIC, SMOOTH, MINIMAL.
David Bradshaw
David Bradshaw
Blackhawk
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Confusion continues to surround the forcing cone. I shall try to clarify points made above, and why I consider the forcing cone integral to accuracy, as important as chamber exit holes ("throat") and the rifled bore itself.
* Question: Is the 11-degree included angle cone good?
Answer: YES. This is the industry standard, the LINK between chamber and bore. In the old days, the forcing cone was concentric and shallow, allowing for bullet support between chamber and rifling. When the forcing cone is too deep, the bullet jumps across a space between chamber and rifling, unsupported. Bullet tilt and obturation result.
* Question: My forcing cone looks rough. Should I ream it?
Answer: NO. Not unless you really know what you're doing and can do the job with a minimum of stock removal, while holding the tool dead-nuts STRAIGHT & CONCENTRIC!
*Question: Would I be better off taking it to a known quality revolver smith?
Answer: YES YES YES.
* Question: Does a hand held reamer straighten a tilted forcing cone?
Answer: NO. It follows the mistake.
* Question: How to correct a deep, tilted forcing cone?
Answer: Remove barrel, turn shoulder on lathe, set back (same as for removing forcing cone erosion). True or cut forcing cone on lathe.
* Question: Old revolvers generally have a shallow forcing cone. Why do some revolvers, starting around 1980, have a deep forcing cone?
Answer: Handgun silhouette started a trend to consume large volumes of magnum ammunition, which produced erosion at the barrel "face"----beginning of the forcing cone. Alignment and timing issues aggravate erosion. A revolver out-of-time or suffering from forcing cone erosion spits powder and bullet particles from the cylinder gap. Called "spitting."
As a hedge against spitting, service departments at both S&W and Ruger cut deeper forcing cones. Deeper forcing cones began to show up on new guns. The result was a deterioration in accuracy.
* Question: Can a deep forcing correct excess chamber-to-bore runout, or oversize chamber exits?
Answer: NO.
* Question: Why not?
Answer: Misaligned bullet ricochets off deep forcing cone----bullet obturation. A bent, unbalanced bullet cannot fly straight.
JOB
As its name implies, the job of a forcing cone is to force the bullet into the barrel. (In a rifle, with the chamber integral with the barrel, the lands gently ramp to introduce the bullet to the rifling. Called "leade." If the leade is rough or abrupt, it tears the bullet, ruining accuracy.)
David Bradshaw
* Question: Is the 11-degree included angle cone good?
Answer: YES. This is the industry standard, the LINK between chamber and bore. In the old days, the forcing cone was concentric and shallow, allowing for bullet support between chamber and rifling. When the forcing cone is too deep, the bullet jumps across a space between chamber and rifling, unsupported. Bullet tilt and obturation result.
* Question: My forcing cone looks rough. Should I ream it?
Answer: NO. Not unless you really know what you're doing and can do the job with a minimum of stock removal, while holding the tool dead-nuts STRAIGHT & CONCENTRIC!
*Question: Would I be better off taking it to a known quality revolver smith?
Answer: YES YES YES.
* Question: Does a hand held reamer straighten a tilted forcing cone?
Answer: NO. It follows the mistake.
* Question: How to correct a deep, tilted forcing cone?
Answer: Remove barrel, turn shoulder on lathe, set back (same as for removing forcing cone erosion). True or cut forcing cone on lathe.
* Question: Old revolvers generally have a shallow forcing cone. Why do some revolvers, starting around 1980, have a deep forcing cone?
Answer: Handgun silhouette started a trend to consume large volumes of magnum ammunition, which produced erosion at the barrel "face"----beginning of the forcing cone. Alignment and timing issues aggravate erosion. A revolver out-of-time or suffering from forcing cone erosion spits powder and bullet particles from the cylinder gap. Called "spitting."
As a hedge against spitting, service departments at both S&W and Ruger cut deeper forcing cones. Deeper forcing cones began to show up on new guns. The result was a deterioration in accuracy.
* Question: Can a deep forcing correct excess chamber-to-bore runout, or oversize chamber exits?
Answer: NO.
* Question: Why not?
Answer: Misaligned bullet ricochets off deep forcing cone----bullet obturation. A bent, unbalanced bullet cannot fly straight.
JOB
As its name implies, the job of a forcing cone is to force the bullet into the barrel. (In a rifle, with the chamber integral with the barrel, the lands gently ramp to introduce the bullet to the rifling. Called "leade." If the leade is rough or abrupt, it tears the bullet, ruining accuracy.)
David Bradshaw
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