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Old November 21, 2012, 11:09 AM   #36
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 10,327
Quote:
Originally Posted by Salmoneye
I'll have to read the Dupont link tomorrow, but I'll take your word that nothing in the data shows anything resembling "SEE"...

Back to square one?
I think this is mixing apples and oranges. Probably my fault. My point in bringing up the old pressure study data is that it shows the effect of large surface area ignition and also that large surface area ignition is not the same thing as detonation. It's just powder starting to burn faster than normal. However, Norma had examples of such loads that did create excess pressure up on their site at one point (I can't find a link now; will have to look further). I think it is a common confusion that all sources of high pressure due to underfilling the case are the same. Wide area ignition involves larger quantities of powder than detonation. Detonation would cause very local fracturing of metal at the powder mass location, after which if only takes only a few hundred psi (about all the tiny charge's gas quantity can muster) to spread the cracks and complete disassembly of the gun.


Quote:
Originally Posted by Salmoneye
And isn't that supposed to be small charges of SLOW powders in large case?...
...I have never heard an SEE warning for fast powder till mid-post #14...
Here's the source: This page has brief mention of a .308 blown up by a Finnish gun writer (who didn't previously believe in the existence of SEE's) using 0.2 grams (3.1 grains) of Vihtavuori N320, a pistol powder about like PB and Accurate #2 in burn rate (between Bullseye and Unique), under a Lapua D-46 type bullet. It says he nearly lost his eyesight despite wearing shooting glasses. (The English is not great on that site and the mention is broken into two different paragraphs; just over 1/2 way down the page).

What's important to note is that unlike "Bullseye Surprise" in .38 Special target loads, the effect of tiny charges in large case volumes cannot be explained away by double charges. You would have to overcharge the case about 7 times just to get to normal .308 pressures in that described incident. It also goes to Brian's point that it is better to err on the side of excess caution rather than the other way.


Quote:
Originally Posted by Salmoneye
. . . but the fact that no powder, bullet, or component manufacturer, has ever been able to define/describe/repeat 'SEE' to me is very telling...
And that may be untrue, now. I'll see if I can get Rocky to cough up the source of his information that labs have more recently figured out how to reproduce it. Technology is always advancing, of course.
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