doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Blow Up Post-Mortem Part 2

Drew, this was mentioned on the first thread but didn't see any comment from you. Does the plastic hull show the imprint of the damascus twist on it?

I think your 'bulge' observation is correct Drew.

This would appear to not be an over pressure caused chamber explosion at all.

My vote would be something stuck in the forcing cone.

Joe: the crolle pattern was not imprinted onto the hull

And BTW: in the name of science I tried some Birchwood Casey Stock Sheen & Conditioner on the barrels and it clearly cleaned off oxidation and years of crud, added lustre, and enhanced the pattern contrast. I was impressed and wish I had a 'before' pic for comparison

oh boy...oh boy...oh boy...more barrels to play with just arrived! This is better than Christmas

Re the comments concerning "approaching SAAMI" limits:

The shooter was using a recipe of 17.5 grains Clays. His loads were relatively consistent, a couple a little under, one a little over, one 0.3 grains over at 17.8. If we extrapolate from the Hodgdon data, which tells us that a 17 grain powder charge is 8200 LUP and an 18.4 grain powder charge 9500 LUP, then it looks like for each additional 0.1 grain of powder, the pressure increases by about 100 LUP. So, at the heaviest powder charge measured (17.8 grains), that would be about 9000 LUP. Add 1,000 to get psi: 10,000 psi. Yes, I'd say hot for a gun of that vintage . . . but still well under the SAAMI service pressure limit of 11,500 psi. And even under the CIP service pressure ceiling of 10,730 psi for a "standard proof" gun. I'd add that I've seen 9500 psi listed as the service pressure for old American 2 5/8" 12ga loads--but that was from pre-WWII sources, so it would actually be 9500 LUP, or about 10,500 psi. So the load should have been safe . . . but not by the safety margin most of us would like to see in vintage guns.

Glad to see other old-time vets chiming in with saltpeter as the supposed additive to Army chow to keep our raging testosterone under control.

Drew, sorry about the 2 7/8", I did mean to write 2 5/8".

It sure looks like a bilge to me, has from the beginning. Realize also an obstruction this close the the chamber is going to react a bit different than one down at mid barrel. Velocity of the charge is not very high yet so the "Check" is not near so great. While pressure would likely still be greatest at the point of the obstruction, it is also likely that pressure would have increased in the entire chamber up until relieved by the burst. I think you need to try & figure out just what was in that barrel & Why & How it got there. I do not believe that either the gun, nor the load being used, was responsible for this burst.

I agree with Miller. I do not believe it was a double charge, but some obstruction.

I might be misunderstanding you but, whatever caused it was an overpressure issue, whether an obstruction, an overcharge, whatever. From the photo I see that left primer shows signs of high pressure. High pressure is the direct result of an obstruction. If, however, it was an obstruction, IMO it had to be directly in front of the chamber. The "common scenario" I can come up with for that is a base wad being "sucked out" of the case an lodging there. And with the Gun Club hull, it can't be a loose base wad as they are of unibody construction.

One possible scenario would be this: Powder bridged causing a double drop, the shell with no powder just ahead of it on the press was used in the left barrel just prior to the blowout leaving it's wad in the forcing cone, by sheer "luck" the next shell loaded in that left chamber was the double charged one. Combination of an overcharge and a forcing cone obstruction equaled what we see. One would think that if this had occurred the shooter would have noticed the blooper and checked the barrel, however. This is all conjecture, of course, but within the realm of possibility. I know where there is a Boswell that blew almost exactly like this, and it was caused by too hot of a reload.

SRH

Stan: By 'over pressure' I mean a shell loaded 'over pressure', i.e. a loading error.

Since the barrel isn't blown where the pressure is normally the highest, rather the 'bulge' shows just downstream of the forcing cone, no 'double charge' would be necessary to achieve the observed results.

But, as you apparently agree, the direct forensic evidence of a double charge is gone. We can only speculate on that, but we can see the bulge.