doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Effect on pressure when the crimp doesn't open?

TW;
I also recall reading a statement by a balistition but likewise cannot remember who nor where. I seem to recall though it was in some old loading manual I had. Anyway he stated he could load a shell to about any pressure level you wanted just by varying the crimp.
Keep in mind that smokeless & black are totally different in their behavior. Black ignites easier & then burns at essentially the same rate regardless of conditions.
Smokeless on the other hand is harder to ignite & normally requires some resistance to build pressure. Once it starts to burn though the more pressure it builds the faster it burns & thus the more pressure is built. Retard it just a bit too much & it can become dangerously high, even with the crimp opening normally. If the crimp holds long ough to break an otherwise good condition case I would have Absolutly No Doubt that chamber pressure would be excessive, irregardless of the actual breaking strength of the case.
I recall an article by Don Zutz once where he had tested some shotshells using plain white flour as a buffer. As long as they were fired fresh pressures were normal. After sitting for a while though the flour attracted moisture & caked & clung to the walls of the roughened walls of the previously fired hulls. Pressures went dangerously high. I highly suspect if you had of had some of those loads with the Mono Wads which stretched the cases pressure tested you would have found them excessive as well.

Regarding new shells -- Roster's test showed that a new, unfired shell had lower velocity (10-20 fps) than those fired subsequently. His hypothesis is that the interior of a previously-fired shell was scuffed up, and held the wad back a bit, versus a slick-walled new shell.

Thank you all for the input. This thread quickly turned in to an interesting read for me. What I am trying to figure out is whether I should be concerned about shooting these shells in my vintage guns. Let me also add that Dan at Nice Shot has been a pure pleasure. Super nice guy and seems willing to provide just about anything his customer wants.

The shells I received are brand new blue shells. I'll try to post a photo of the damaged hulls in a little bit.

Here are other variables to consider, of which I have no idea what is or is not of any value:

The temperature was about 45 degrees, probably warmer.

I ordered 2-3/4" shells. They all measure between 2-3/8" and 2-1/2" and are all shorter than any of my name brand factory 2-3/4" shells, and about the same as the my 2-1/2" RST shells. I thought he had made a mistake with the order so I asked him about that. He emailed back that the hulls all measured 2-3/4" WHEN OPEN. I always thought a 2-3/4" shell was longer than 2-3/4" when open, but a little research on the 'net tells me length is based on the spent hull. He also speculated he must have had the dwell on his roll crimper set a little too high as the reason why they didn't open properly. He said it uses friction to heat set the crimp. The recipe is supposed to produce 8000psi, but I definitely recall noticing the recoil as compared to lead RST loads. Whatever that non-scientific observation is worth.

What, if anything, does the overall length of my shells (2-1/2") tell you about the crimp depth, potential pressure produced, etc? Other thoughts? I'll try to get that picture loaded.

Here are the hulls after being fired.

Could you show a before picture ?

I've read the same thing. Can't say I ever sent any off for pressure testing, greater crimp depth vs less depth. But as best I remember from what I read, greater depth=more pressure; less depth=less pressure. The source might be one of the powder companies, or maybe a reloading manual.

I believe in one of Tom A's articles he showed pressure changes with a .030,.060 and .090 crimp depth. It was significant. I'll try to find the reference.

Found it!
Here is the link. About 2/3 of the way down on the right in a table.

http://www.armbrust.acf2.org/primersubs.htm

From the photo, it look's to me like he is using way to much hull material to turn the crimp. I use a roll crimp a lot and turn just enough to roll the edge over. Probably just under 1/4 inch and I do not use friction (heat) to set the crimp. Heat causes the plastic to turn brittle and make the hull very hard to open easily. I have reloaded nice shot and not experienced any problems with crimping the hulls. Using Cheddite plastic or paper hulls I have never experienced that problem and my fired hulls can be reloaded by hand rolling them on a wood dowel to even out the hull mouths. Too much material in the crimp and too much friction to set the crimp is my thought.

I thought the same thing as you Eric, heat made the the roll brittle. My guess

I took my pictures to our local blackpowder shop here in town. He didn't look at it very long before asking about my chamber length, saying it looks like the hulls didn't have room to open. I believe a 1898 Parker GH should measure 2-5/8" chambers with Parker recommendations to use 2-3/4" shells so that does seem a plausible explanation. I'll get the chambers measured to know their length for sure. Please comment if anyone sees anything amiss with the way those remaining shells look to you, or if my local guy's theory holds water.