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Joined: Apr 2004
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Sidelock
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Sidelock
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Ballistic Products has lots of stuff for your desired intention. Components and data.
Ms. Raven
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Joined: Feb 2012
Posts: 19
Boxlock
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Boxlock
Joined: Feb 2012
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I sent you a private message, thank you answer me as soon as you can cordially KirkD, welcome.
Many of us load low pressure 2 3/4" hulls for our 2 1/2" chambered guns with good satisfaction. The issue with 2 3/4" hulls in a 2 1/2" chamber gun is when higher pressure loads are used. Higher pressure loads tend to have a higher pressure differential than do low pressure loads.
The 7000 psi recommendation is a sort of rule of thumb based on being conservative with black powder loads and service proof as a guideline. BTW, many BP loads have high chamber pressure; they are not universally low pressure as is sometimes said. There are many low psi 2 3/4" loads in the various loading manuals and web sites. Pick one below 7000 psi (more or less) that you have exact components for and have fun. I shot five-stand last Sunday with a Parker "D" with damascus barrels and can still count to ten on my fingers!!
DDA I sent you a private message, thank you answer me as soon as you can cordially
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Joined: Jan 2002
Posts: 11,398 Likes: 108
Sidelock
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Sidelock
Joined: Jan 2002
Posts: 11,398 Likes: 108 |
Clays/Claydot and Alliant's relatively new Extra Light are other powders that will produce low pressure loads for vintage guns, whether they're Damascus or fluid steel.
Kirk, I reread the Bell article on long shells in short chambers not too long ago. In most cases, the pressure increase when using a 2 3/4" hull vs a 2 1/2" hull is relatively small, on the order of a few hundred psi. However . . . on some Damascus guns, with very short and sharply tapered forcing cones, you'll find that you need to stick to the short hulls. Appears to be not so much the chamber length, but rather the nature of the forcing cone. Bell also discovered that just lengthening the cone without modifying the chamber usually resulted in some reduction in pressure.
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Joined: Jan 2006
Posts: 15,456 Likes: 86
Sidelock
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Sidelock
Joined: Jan 2006
Posts: 15,456 Likes: 86 |
Last Dollar: Most fellows around here use high speed rifles that fire a bullet at nigh unto 4,000 fps and shoot them from 400 yards away. That makes it way too easy. I like to stalk up to about 20 yards away and then let them have it. I've done this for a number of years with a 20 Bore, but now that I have this old hammer gun, I want to use it for the Woodchucks. They are making big holes in my alfalfa field.
Chuck you should try woodchuck stalking it's great sport.
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Joined: Feb 2012
Posts: 19
Boxlock
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OP
Boxlock
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Men, I wrote to Sherman Bell to see if he had tested black powder cartridges to see what sort of pressures they generate. He mentioned that he had compared smokeless and Black powder pressures in two articles in the Winter 1999 and Summer 2002 issues of Double Gun Journal. He also mentioned that full power black powder loads produce from 6,000 to 8,000 psi breech pressure. By 'breech' pressure, I think he is referring to the hoop stress in the barrel near the breech (from how he uses that term in another article he wrote).
So that fits with the advice that has been given in this thread, but it is nice to have an idea where the upper limit is so one knows whether they have 7,000 plus or minus 5 psi to play with or 7,000 plus or minus 800 psi.
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Joined: Jan 2002
Posts: 5,954 Likes: 12
Sidelock
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Sidelock
Joined: Jan 2002
Posts: 5,954 Likes: 12 |
I'm back in the land of internet. Be with you shortly - I do have your messages and have the information - just need a wee bit of time to sort out the correct stuff.
DDA
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Joined: Jan 2002
Posts: 5,954 Likes: 12
Sidelock
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Sidelock
Joined: Jan 2002
Posts: 5,954 Likes: 12 |
Men, I wrote to Sherman Bell to see if he had tested black powder cartridges to see what sort of pressures they generate. He mentioned that he had compared smokeless and Black powder pressures in two articles in the Winter 1999 and Summer 2002 issues of Double Gun Journal. He also mentioned that full power black powder loads produce from 6,000 to 8,000 psi breech pressure. By 'breech' pressure, I think he is referring to the hoop stress in the barrel near the breech (from how he uses that term in another article he wrote).
So that fits with the advice that has been given in this thread, but it is nice to have an idea where the upper limit is so one knows whether they have 7,000 plus or minus 5 psi to play with or 7,000 plus or minus 800 psi. Not exactly, Kirk. Breech pressure is the peak/maximum pressure generated within the barrel and occurs before the payload (shot & wad) have moved into the barrel bore proper; this max pressure is within the chamber area and decays quickly as the payload starts to move. Hoop stress (the actual stress on the barrel steel) is calculated from knowing the barrel (chamber) ID, OD (hence, wall thickness), and breech pressure. Bigger diameters, thinner walls, and higher pressure cause higher hoop stress on the steel. The barrel profile is such that the hoop stress is never in excess of the yield strength (point where the steel bulges) of the steel. Per above, the pressure drops as payload moves down bore; so, the barrel walls may be made thinner. Questions? DDA
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Joined: May 2004
Posts: 2,092 Likes: 13
Sidelock
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Sidelock
Joined: May 2004
Posts: 2,092 Likes: 13 |
For thin walled cylinders, hoop stress is calculated by multiplying the radius by the pressure in psi divided by the wall thickness. Based on this, if you have a smaller radius (12g. down to 20g for example)you can have higher pressure with the same wall thickness and still maintain the same hoop stress. This from Wikipedia. Also from Wikipedia: Fracture is governed by the hoop stress in the absence of other external loads since it is the largest principal stress. Note that since the hoop stress is largest when r is smallest, cracks in pipes should theoretically start from inside the pipe.
Seems contadictory. Am I misunderstanding this?
So many guns, so little time!
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Joined: Feb 2012
Posts: 19
Boxlock
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Boxlock
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Rocketman, you are right. I don't know what I was thinking; chamber pressure is not the same as hoop stress. Looking at the other article I mentioned, Bell calculated the chamber pressure by measuring the hoop stress via a strain gauge mounted on the barrel. The strain gauge measures the hoop stress, which can then be used to calculate the chamber pressure. The photos of his pressure traces show the 'EST' pressure, so I imagine he caliberates the output of the strain gauges to trace the hoop stress curve in terms of chamber pressure, easy to do since hoop stress is directly proportional to chamber pressure.
Last edited by KirkD; 03/06/12 10:53 AM.
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Joined: Jan 2002
Posts: 5,954 Likes: 12
Sidelock
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Sidelock
Joined: Jan 2002
Posts: 5,954 Likes: 12 |
For thin walled cylinders, hoop stress is calculated by multiplying the radius by the pressure in psi divided by the wall thickness. If pressure and wall thickness remain constant, a larger radius causes a larger numerator which would be divided by a constant demominator; hence, a larger hoop stress. Based on this, if you have a smaller radius (12g. down to 20g for example)you can have higher pressure with the same wall thickness and still maintain the same hoop stress. Well, lets just work the numbers. We do need to use mean radius (mean radius is half ID + half wall thickness, say 0.730/2 + 0.100/2. For 12 bore = 0.365" +0.050" = 0.415", assuming wall thickness at 0.100", Assume pressure at 5,000 psi. Then 12 bore hoop stress equal (5,000 X 0.415)/0.100 = 20,750 psi stress (pressure and stress have the same measurement units). For 20 bore, r = 0.615"/2 + 0.100/2 = 0.3575"; hoop stress = (5,000 X 0.3575)/ 0.100 = 17875 psi or, r for = (5,000 X 0.3505)/ 20,377 = 0.086". Yes, you are right!!This from Wikipedia. Also from Wikipedia: Fracture is governed by the hoop stress in the absence of other external loads since it is the largest principal stress. Note that since the hoop stress is largest when r is smallest (nope, when r is largest), cracks in pipes should theoretically start from inside the pipe (nope, the outside should fail first). Seems contadictory. Am I misunderstanding this? Yes, I think so - as above. You were right to start with and then went astray. OK?. DDA
Last edited by Rocketman; 03/06/12 09:01 PM.
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