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Post by bradshaw on Jan 19, 2015 1:15:15 GMT -5
Markbo.... any dimension which facilitates the bullet leaping from cartridge case into bore without getting beat up is a good thing. The forcing cone is a necessary evil, forced on us by revolver chambers separate from the bore. The farther a bullet under pressure travels with its "wheelbase" unsupported the more speed it picks up, and the more opportunity it has to tilt. At magnum pressures a bullet may obturate before it gets into the rifling. Dan Wesson found this out when firing bullets from cylinder to atmosphere----firing with barrel unscrewed from cylinder frame. David Bradshaw
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Post by Lee Martin on Jan 19, 2015 18:25:47 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?? Centering off the grooves is more reliable than the lands. Bottoming the dial finger on them is easier and land heights often vary by a few tenths (even on some of the higher end blanks). Concerning shallow cone depths, I always infer proper throat-to-bore alignment. On our conversions, we index well under 0.001". And that's not a guess, each of our chambers is gauge tested. To my way of thinking, properly center the two and I want the bullet into the lands ASAP. Less chance for tilt, less chance for it to obturate. David Bradshaw has done a wonderful job documenting why forcing cones grew on production guns. Let indexing become lax, allow dimensions to wander, and fit cylinders way less than near rigid, and the forcing cone (or unnamed throating techniques) picks-up the slack. Sometimes they produce good results, other times they snuff good precision. Regardless, I view generous cones and free-bore as shortcuts. -Lee www.singleactions.com"Building carpal tunnel one round at a time"
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Odin
.375 Atomic
Posts: 1,058
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Post by Odin on Jan 19, 2015 19:45:22 GMT -5
Lee, David,
What would be the prescription then for a revolver with a long, rough cone? My guess would be to have the barrel set back and to start over fresh.
I purchased a Virginian Dragoon (stainless, 7.5-inch, 44mag.) as a project gun, or more accurately, a learning gun. My thoughts were to tune the trigger, shorten the barrel, put it on my hip and go for a long walk. It is a fine gun in all respects, save two- the trigger (tons of creep) and the forcing cone, which is very long and very, very rough.
I'm not terribly concerned about the trigger, but that cone... It's quite long, probably on the order of 3/8-inch., and rough to the point that I figure a little work with a rasp would smooth it up considerably (kidding, somewhat). And I might point out that while I'm generally ignorant of such things, the diameter at the face of the cone seems rather large- I have nothing to measure it with, but a 45 Colt case will slip in about 1/16-inch or so, maybe a bit more.
-Rod
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Post by bradshaw on Jan 19, 2015 22:38:51 GMT -5
Rod.... your first paragraph covers it.
A rotten forcing cones ruins the barrel. Either set back the barrel and do the forcing cone right or replace the barrel. Doug Shilen showed me that a lousy chamber job ruins a great barrel. You've got to start the bullet on its brief journey sweet as mechanically possible to keep your mind making the shot clean as possible.
To tilt a bullet, to bend a bullet, to mash a bullet warps gyroscopic balance. Start with a proper firearm. Add a proper bullet seated over powder it likes. Breathe and squeeze. The life of a bullet inside the gun is short, yet long enough for things to go wrong. We own our eye we own our breath we own the trigger.
Play each shot for keeps. David Bradshaw
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Post by bradshaw on Jan 19, 2015 23:08:36 GMT -5
*
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Odin
.375 Atomic
Posts: 1,058
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Post by Odin on Jan 20, 2015 0:10:03 GMT -5
David, thank you for your insight and advice. I will put it into practice.
The gun was originally part of the estate of a firearms enthusiast from upstate New York who carved out a second career making control boards for fireworks displays (cherished the BOOM, I guess). I won it on a lark at auction (without full inspection) reasoning to myself that it would be a good learning tool- and to my wife that it was cheap. It came with a B-Square scope mount that attached to the barrel and in my mind indicated the original owner worked hard to make it shoot straight but then gave up, retiring it to safequeen status. Of course that last bit is pure conjecture on my part, but the overall condition of the gun suggests that it was shot and handled rather minimally.
As mentioned earlier, it is mechanically quite fine with action moving slick and smooth, reminding me of my father's Python and tolerances that equal, if not better, those found on my BFR. Grips are smooth and full and fit better to the gun than any production grips I have ever seen. The hammer would be death to a gunfighter though and amuses me greatly in its slow deliberate arc, like that of the quarryman's sledge. Should be a good tool for disciplined training... and a steady hand.
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Post by bradshaw on Jan 20, 2015 11:14:15 GMT -5
Rod.... if silhouetter Boyd Carpenter listens in, he may shed light on Virginian Dragoons beyond my experience. My experience is limited to Silhouette Dragoons made under Rod Sward at the Factory in Virginia. My testing at 100 yards and meters 10" Dragoons in .357 and .44 mag turned accuracy in the 2-1/2" range for five shot groups, firing Creedmoor with the iron sights. These revolvers had bullet diameter freebore, and showed to my satisfaction freebore may help straighten a revolver's introduction into the rifling. These Silhouette Dragoons had short, smooth forcing cones.
Have no experience with the conjunction of a crap forcing cone to freebore, thus can only speculate on ability of freebore to straighten a bullet made crooked by slamming into the forcing cone, especially if the heal is not supported by the chamber throat.
Unsure whether you may truly discern accuracy of your Dragoon sighting through a scope clamped to the barrel via B-Square mount. I have never been able to trust that arrangement above .22 rimfire, and ain't exactly in love with it there.
Process of elimination * remove B-Square mount. * shoot sandbag or Creedmoor groups as far as possible out to 100 yards. * upon results at target, decide whether to: a) keep pistol as is. b) fix pistol. c) sell pistol.
David Bradshaw
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Post by bradshaw on Jan 20, 2015 13:42:36 GMT -5
Rod.... the long hammer fall you experience on your Interarms Virginian Dragoon is a function of the cocking geometry, involving pawl & cylinder ratchet. The hammer is tall, its arc long; and, as you note, smooth. A shooter practiced in follow-through may shoot these revolvers very well indeed. People with a nervous twitch should expect a rougher time. When sights lurch off target during hammer fall, the bullet follows. Intrinsic accuracy of the better Virginian Dragoons might have positioned the revolver in or about the winners' circle in silhouette. The Dan Wesson Arms M44 came along and stepped on Daniel Boone's coonskin hat. David Bradshaw
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Post by bradshaw on Jan 20, 2015 13:44:13 GMT -5
*
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Post by Markbo on Jan 20, 2015 18:13:33 GMT -5
Shooters with a nervous twitch..thats funny stuff.
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Post by riorider on Mar 22, 2015 19:27:35 GMT -5
I was told by a an enginener that the combustion flames are always burning at an 11 degree angle so crowns and or cones are less attacked by flame cutting if at that magic angle! Who Knew?
Tommorrow is a new day and we get to start over again!
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Paden
.375 Atomic
Lower Goldstream Creek
Posts: 1,132
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Post by Paden on Mar 22, 2015 20:12:17 GMT -5
I was told by a an enginener that the combustion flames are always burning at an 11 degree angle so crowns and or cones are less attacked by flame cutting if at that magic angle! Who Knew? By chance, did this conversation take place in a bar?
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Post by seancass on Mar 23, 2015 6:21:43 GMT -5
I'm not really aware of anything in engineering that happens at 11*. I've never seen pictures or vids of muzzle flash and thought it was burning at an 11* angle.
To my mind, I'd like a cylinder perfectly aligned with the bore. Instead of a forcing cone, just tapered rifling and zero cylinder gap. From that standard back to reality it's all compromise.
I'm curious how my above theory based on extremely limited knowledge compares with the experience of those posting above me.
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Post by bradshaw on Mar 23, 2015 21:12:30 GMT -5
seancass.... what you want to see we all want----zero punk dimensions. The .000 cylinder gap isn't doable, but, given a square cylinder face and zero endshake on a gun that isn't made out of rubber, .001-inch is doable. You may subtract cylinder gap from your list of coordinations, since gap plays just about zero part in accuracy. Velocity, gap hurts. David Bradshaw
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Post by riorider on Mar 25, 2015 12:12:25 GMT -5
No it took place in my gun shop BUT we know engineners can over work a fart and make it like a rose! You listen to it all and use what ya can and throw out the rest!
Tommorrow is a new day and we get to start over again!
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