Detonation, another myth?

Hitzy said:
17 thou is nothing, not for new brass anyway, should be able to handle that easy....and that starting load would not have been 60,000psi.
Something else going on there.
Pretty much every Nork M14 out there is running 15-20+ thou over 308 specs and there are probably millions of rounds through those combined. Steel cased don't seem to handle it so well however.
The case head looks very thin in the pics, and I don't see any signs of brass flow anywhere, just the case coming apart.
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When the max SAAMI headspace range is .004" then .017" is a huge variance. You are going to need to back up your claims that Chinese M14 copies are routinely running wildly excess headspace cause I don't believe it for a second.

The SAAMI dimensions exist for a reason and grossly exceeding them will eventually result in ruptured cases. When it happened to me, I got through a bunch of cases before one blew but even going in I knew they chance that this would occur. It was simply an eventuality.

I fully believe SEE can occur but it is very difficult to induce. Separated cases from excess headspace on the other hand are extremely easy to induce. Occam's Razor at work.
 
Suputin said:
When the max SAAMI headspace range is .004" then .017" is a huge variance. You are going to need to back up your claims that Chinese M14 copies are routinely running wildly excess headspace cause I don't believe it for a second.

The SAAMI dimensions exist for a reason and grossly exceeding them will eventually result in ruptured cases. When it happened to me, I got through a bunch of cases before one blew but even going in I knew they chance that this would occur. It was simply an eventuality.

I fully believe SEE can occur but it is very difficult to induce. Separated cases from excess headspace on the other hand are extremely easy to induce. Occam's Razor at work.
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You gotta read the battle rifles forum more often.....
Now this was from 2005, and brass is measured for the headspace with precision mics, so add a thou or 2 to those measurements.
http://www.canadiangunnutz.com/foru...ng-the-M-14-amp-Headspace-Myths-in-Norc-M14-s
Most of the NEW Norinco clones I've checked recently had about .012 - .014" headspace over .308 Win GO. If you do the math, you can see the THEORETICAL SAAMI safety margins are being exceeded by quite a bit. But in the real world, I've seen M-14 rifles with MASSIVE headspace that functioned safely and flawlessly AS LONG AS YOU USED ONLY 7.62 NATO AMMO. The brass in 7.62 NATO is THICKER and HARDER than commercial .308 brass.
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My 2013 Nork fired brass is 15thou over 308 min spec or 16-17 thou if gauged, most of the recent ones are like that.
http://www.canadiangunnutz.com/foru...-m305-Cal-7-62mm/page2?highlight=2013 marstar
 
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My M305 was 14 thou over go Guage.

Since I was planning on reloading I dropped in a new bolt.

Shot with the oversized chamber with no issues. Most brass I measured, that was sent to me, measured 5-15 thou over go gauge.
 
FUUUUKC glad I don't know one of those things. :(

However that doesn't preclude the Carcano explosion from having been a headspace issue. The M14 info specifically notes the use of NATO brass which is considerably thicker in the web. A headspace relate issue is still considerably more likely than SEE, especially when he wasn't using a really light load.
 
Eagleye said:
This detonation, or SEE, is NOT a myth. It occurs with reduced charges of slow-burning powder.
Certain powders used to have a warning acompanying them regarding using too low a charge weight.

As has been mentioned, the phenomenon cannot be duplicated at will, but occurs without warning.
I had a personal experience many years ago with old W785 in a 308 Norma Magnum. It did not destroy
my rifle, but the signs of extreme pressure were very evident. After beating the bolt open with a 2x4,
the case came out and the primer fell right out of the case. The head of the case was heavily marked,
and it measured .536" across the belt. I was shooting a charge that gave me about 2400 fps with a 180,
and had shot quite a number before the kaboom happened. All the others acted absolutely normally. I
changed over to IMR 3031 for my reduced loads, and never had a prblem again. Dave.
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I agree 100%, my favorite powder for my old .270 was W785 and it was discontinued because of the detonation problem. The Winchester load data specifically said not to use loads lower than listed.
 
I have researched this topic a lot and have developed a theory. Firstly this phenomenon was quite prevalent when using reduced loads of surplus H 4831 in the newly introduced magnum cartridges in the late 50s and early 60s. Since then it has been noted with other very slow powders such as W-W 785 and a few others. I believe the reason it cannot be reliably repeated is that it has to do with the way the powder lies in the case. It is my theory that if the powder is laying just so, so that the primer flashes over the top of the entire powder charge at the time of ignition, it ignites a huge cross section of the powder at the same time. This would have the effect of reducing ignition and burn time of the progressive burning powder, to a burn rate akin to Unique or even Bullseye. In this scenario almost 1/2 of the available powder would be lit at the instant of ignition, which in turn produces an extreme initial pressure spike and burns the remainder of the powder almost instantly, negating its inhibitors and radically changing it's burn rate. I also believe that only powders with certain nitro contents and certain inhibitors used when making and coating slow burning powders, is the reason that this phenomenon is limited to a very small number of slow burning rifle powders, when used with less than 60% case fill.
This is a problem I'll never have, given my loading habits..........;);)
 
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