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< 16ga. Ammunition & Reloading ~ Chamber pressure/crimp depth |
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Posted:
Fri May 25, 2007 1:18 pm
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Member
Joined: 28 Oct 2005
Posts: 665
Location: Louisiana
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As there is considerable interest in reloads with lower pressures for older guns (as well as some new ones) I thought this information might be of interest.
This information suggests a nominal crimp depth of .050 (1/16" m/l).
Crimp depth-----------PSI
.030 -----------------9,300
.050-----------------10,500
.070 ----------------11,900
.090-----------------13,100
All data was collected on shells using the same components. |
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Posted:
Fri May 25, 2007 2:22 pm
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Member
Joined: 09 Apr 2005
Posts: 339
Location: Schuyler County, NY.
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Guess this is good info but I have a hardtime understanding how .020 increases pressure by 1200 psi. or .060 which is almost 1/16" causes a pressure rise of 3800 psi. Like I said --good info but I wonder where it came from |
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Posted:
Fri May 25, 2007 6:55 pm
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Joined: 05 Mar 2007
Posts: 61
Location: Out in some godforsaken marsh
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I hope that's not accurate. I agree with Billy that it sounds like quite a bit of pressure increase for 1/16" of crimp depth.
Skip |
_________________ The Snipe Hunter |
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Posted:
Sat May 26, 2007 4:40 am
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Member
Joined: 27 Jun 2005
Posts: 1545
Location: Michigan
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I agree, I don't know where that data come from. But I don't believe it. |
_________________ What one person receives without working for, another person must work for without receiving. |
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Posted:
Sat May 26, 2007 5:04 am
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Member
Joined: 08 Apr 2006
Posts: 104
Location: Northeastern Pa.
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Woodcock, I could see where this could be a problem becasue you are putting more pressure into a smaller area. I also believe that you would start to see the shell bulge when you went too deep. In using Mec reloaders most wad pressure is just enough to seat the wad.
In the last one of .090 that is almost 3/32", that's pretty deep for a crimp.
I'm guessing that you had these shells with the different depth crimps sent for pressures testing?
Also I wouldn't consider even the first one as being low-pressure. |
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Posted:
Mon May 28, 2007 8:14 pm
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Member
Joined: 21 Aug 2006
Posts: 113
Location: Phoenix, AZ
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Think fire cracker in open hand vs fire cracker in closed hand. Same charge, significantly different result. |
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Posted:
Tue May 29, 2007 3:35 am
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Member
Joined: 27 Jun 2005
Posts: 1545
Location: Michigan
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chopper wrote: |
Think fire cracker in open hand vs fire cracker in closed hand. Same charge, significantly different result.
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I don't think you'll increase the amount of pressure generated by the firecracker. Just the amount of pain in your hand. |
_________________ What one person receives without working for, another person must work for without receiving. |
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Posted:
Tue May 29, 2007 9:14 am
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Member
Joined: 28 Oct 2005
Posts: 665
Location: Louisiana
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I am not in the habit of posting unsubstantiated information on this site.
You may verify these figures from Hodgdon. They were derived from work conducted by Hodgon [/i]ballisticians using "12 guage shotshells loaded in the same type hull with the same amount of propellant, the same primer, wad and shot charge, ONLY THE CRIMP DEPTH WAS CHANGED."
Ron |
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Posted:
Tue May 29, 2007 10:01 am
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Member
Joined: 03 Dec 2006
Posts: 759
Location: Somewhere in the Socialist State of Minnesota
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I can see how that would happen. Works the same way with water, more crimp, higher pressure. A fire hose nozzle automatically adjusts to the volume to keep the pressure up. Just a little physics from college. |
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Posted:
Tue May 29, 2007 10:43 am
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Member
Joined: 13 Mar 2007
Posts: 142
Location: Michigan's U.P., eh.
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Quote: |
I can see how that would happen. Works the same way with water, more crimp, higher pressure. A fire hose nozzle automatically adjusts to the volume to keep the pressure up. Just a little physics from college.
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From physics to physiology. Same thing happens with blood pressures. When vessels constrict, either on their own or due to blockages, the blood pressure increases as long as the volume remains constant. Thanks for the source of the info. Woodcock. I liked your analogy Oldhunter, made me think about it in other contexts. |
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Posted:
Tue May 29, 2007 12:08 pm
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Member
Joined: 28 Oct 2005
Posts: 665
Location: Louisiana
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Same thing happens when either constant (pressure/volume) changes--a variation of Boyle's Law I believe.
In the case of crimp depth, I suspect that the resistance of the crimp to unfolding is of primary significance as the volume change is minor. However, it is just that sort of 'intuitive' thinking about expolsives that can leave one without a full compliment of fingers.
Keep in mind that a recipe that calls for a 6-point crimp has a different pressure when roll crimped. |
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Posted:
Tue May 29, 2007 10:33 pm
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Member
Joined: 21 Aug 2006
Posts: 113
Location: Phoenix, AZ
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Quote: |
I don't think you'll increase the amount of pressure generated by the firecracker. Just the amount of pain in your hand.
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If you decrease the volume of a container, a hull by increasing crimp debth or a hand by closing it around a firecracker , the psi the reaction exerts on the remaining container increases. Same number of excited molecules bouncing off of a decreased surface area = increased pounds per square inch. The energy that is released in the reaction does not change, just the amount of area the reaction has to work against.
Chopper |
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Posted:
Wed May 30, 2007 8:47 am
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Member
Joined: 28 Oct 2005
Posts: 665
Location: Louisiana
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Posted:
Wed May 30, 2007 4:08 pm
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Joined: 06 Apr 2007
Posts: 70
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what's awkward to grasp is that the pressure buildup is almost instantaneous and the crimp can't be blown open fast enough to relieve it. |
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Posted:
Wed May 30, 2007 5:45 pm
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Member
Joined: 02 Feb 2007
Posts: 1734
Location: Central Missouri
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Hello Woodcock :
You bring logic and learning to the forum.
One thing extra is that the deeper crimp captivates the leading edge of the wad and holds it in place longer and more decisivly thus the pressures mount in a hurry compaired to a load with an over the shot card which allows the crimp to open up at a uniform rate versus a shell using just a crimp alone.
The old Blue Magics used to shoot the ends of the hull off or the whole hull for that matter would go out the end of the bbl if you put a deep crimp on that hull.
I must agree with the testing and data that BPI came up a long time ago concerning this subject just use an over the shot card and see how much nicer your crimps look as well as how consistant the load will be , and I recall the reps putting out the data on the crimps at the trapshoots in the past .
Regards Charles |
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