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< 16ga. Ammunition & Reloading ~ need help with chronograph results |
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Posted:
Sun Apr 16, 2017 7:40 am
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Joined: 08 Aug 2011
Posts: 1946
Location: Central CT
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Reducing max loads 10% for centerfire loads, which means that cannister powders are subject to change by 10% is an incorrect assumption.
Maximum loads for centerfire are completely different than shotshell loads. The major difference is that there are signs of excess pressure in centerfires because of how the bullet engages the rifling, this can and does affect pressures and can be different between firearms and are visible and measurable.
Shotshell chamber pressures are largely determined by the components and the crimp and to a lesser extent the dimensions of the chamber. The brand of firearm for shotshells may affect chamber pressure but not enough for concern, nor are there any visual or measurable signs of excess pressure.
Also the 10% has nothing to do velocity it is strictly a reduction in powder charge as you work back up to the maximum as you look for signs of pressure. It definitely does not mean that canister powders can/do vary 10% lot to lot.
Many of those disclaimers are aimed at the centerfire loads they are not applicable to shotshell loads. |
_________________ Mark |
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Posted:
Mon Apr 17, 2017 2:25 am
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Joined: 15 Dec 2005
Posts: 287
Location: missouri
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So you don't believe there is lot to lot variation with Canister powder???
Carry on then, you'll never believe it obviously. |
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Posted:
Mon Apr 17, 2017 3:39 am
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Member
Joined: 08 Aug 2011
Posts: 1946
Location: Central CT
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While there certainly can be differences lot to lot, 10% is considerable. |
_________________ Mark |
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Posted:
Tue Apr 18, 2017 2:24 am
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Joined: 15 Dec 2005
Posts: 287
Location: missouri
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Dogchaser37 wrote: |
While there certainly can be differences lot to lot, 10% is considerable.
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10% is considered maximum for industry standards and a safety factor for start loads, they can't get every lot of powder 100% within spec every time.
If there wasn't lot to lot variation and they would assume reloaders would follow C.O.L. specs for cartridges, then why specify to start 10% below maximum pressures??? Makes sense to me anyway. |
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Posted:
Tue Apr 18, 2017 2:58 am
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Member
Joined: 08 Aug 2011
Posts: 1946
Location: Central CT
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You really need to understand how pressures differ from centerfire cartridges amd shotshells, especially what creates the pressure.
With shotshells the components and the crimp create the pressures, the barrel has little to do with the pressures, because the resistance is in the crimp as the ejecta does not engage anything creating more friction to overcome.
Not the same animal at all. What is a max load in one centerfire firearm may not be a max load in another firearm using the same exact components. The 10% reduction has to do with the firearm (how the projectile engages the rifling) not the powder charge or its lot to lot variation. How the bullet engages the rifling is the key to determining a max powder charge in a centerfire.
We don't differentiate between shotgun barrels when loading shotshells to max, however you absolutely must differentiate between centerfire barrels when loading max loads.
Two completely different subjects thus the disclaimers and warnings for centerfire reloading. |
_________________ Mark |
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Posted:
Tue Apr 18, 2017 4:01 am
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Joined: 15 Dec 2005
Posts: 287
Location: missouri
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Dogchaser37 wrote: |
You really need to understand how pressures differ from centerfire cartridges amd shotshells, especially what creates the pressure.
With shotshells the components and the crimp create the pressures, the barrel has little to do with the pressures, because the resistance is in the crimp as the ejecta does not engage anything creating more friction to overcome.
Not the same animal at all. What is a max load in one centerfire firearm may not be a max load in another firearm using the same exact components. The 10% reduction has to do with the firearm (how the projectile engages the rifling) not the powder charge or its lot to lot variation. How the bullet engages the rifling is the key to determining a max powder charge in a centerfire.
We don't differentiate between shotgun barrels when loading shotshells to max, however you absolutely must differentiate between centerfire barrels when loading max loads.
Two completely different subjects thus the disclaimers and warnings for centerfire reloading.
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There's been case studies performed by the military on lot to lot variation, interesting reading
http://www.dtic.mil/dtic/tr/fulltext/u2/a572333.pdf |
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Posted:
Tue Apr 18, 2017 5:49 pm
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Member
Joined: 08 Aug 2011
Posts: 1946
Location: Central CT
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Thank you so much for supporting my comments with such a nice article as it shows an approximate 3% & 3.7% difference in velocity. |
_________________ Mark |
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Posted:
Wed Apr 19, 2017 2:31 am
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Joined: 15 Dec 2005
Posts: 287
Location: missouri
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Dogchaser37 wrote: |
Thank you so much for supporting my comments with such a nice article as it shows an approximate 3% & 3.7% difference in velocity.
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True but it shows there is lot to lot variation no matter what anybody wants to believe, which was my whole point. Don't forget also the test was done with H4831 which is single base, with double base powders which many rely on retardants to control burn rate variations could be quite different.
I'm not saying every lot of powder can be off by a whole lot but I won't deny there is lot to lot variation and I won't discount it as a unimportant if there is no other explanation in some cases. |
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