I received some Nice Shot last week and used 4 12ga shells. Of those, 3 did not open properly. The crimps were basically blown off. How does this effect pressure and the pattern?

May not be directly related, but Tom Roster checked the velocities of plastic hulls which were reloaded until they failed. There was no change in velocity between the first reload and the last

I suspect it is OK, I have had LOTS of Federal Steel hulls separate
at the crimp when shooting in cold conditions.

They still kill ducks

Mike

"IF" the crimp did not open at all you would of course have a closed cell pressure which would be astronomical. Any increase in resistance to the crimp opening over normal will increase the pressure. The question here however is was the hull itself just weak & broke easier than opening the crimp. If this be the case there was likely no increase of pressure.
I find that No Change in velocity from an as new shell with firm crimp to one ready to fail a Bit Hard to Swallow.

I too find it difficult to believe that a a new factory shell with a tight firm crimp had the same veloicty as a old used shell. The factory new shell will develope more pressure hence more veloicty, every thing else being equal.

I agree w/Miller's skepticism.

Its been a long while ago, but I want to recall that an article in Wolfe publications Handloader early on that dealt w/pressure & velocity testing repeated reloading's using an original AA CF 12ga. hull and it found that as the number of reloads increased there was a significant drop in recorded pressures as well as velocity. I know, there is no direct corollary between pressure and velocity and that was NOT being implied, rather it was simply observed as I recall. Hey, like Russ always said, I could be wrong. It may have been an article dealing w/crusher methods as well, i.e., LUP, not psi.

I cannot tell from the OP if it was factory loaded ammunition or something that had lead originally and the Nice Shot was used as a replacement. If it was the latter, that is NOT a proper application w/o tested data suggesting such use and it is an open question as to the pressures involved.

I've shot a lot of Bismuth, tungsten iron, Heavi-shot & steel and while the factory crimps on some of it has been 'butt ugly', I've never seen a crimp blow off, even in below freezing weather. Just my experience, not refuting Mike's at all. I don't shoot many Federal non-toxic loads though their newer Black Cloud loads are clearly VERY effective. I'm just not into that level of punishment;-)

I doubt that the hull has sufficient strength in the walls to gen up enough force to hold the shot long enough to cause much, if any, increase in pressure. The hull should fracture at something like 650-700 psi chamber pressure. This would be quite early in the burn. I'll post calculations if anyone is interested.

The pattern might be a different story. If the hull ruptured below the shot column, you might have a "sortaslug." If the hull ruptured at the crimp base, I'd expect it to act like an overshot wad and spin off shortly after muzzle exit with minimal effect on the pattern.

Back in the bad olé days, I loaded AA's until they fell apart. I never noticed any deterioration in clay breaking between new and rag. But, I've never run pressure tests, either.

DDA

If continued reloading results in decreasing pressures/velocities due to a weakening crimp, would a shot card help offset that decrease? My recollection is that shot cards do not have any material impact on pressure.

I think most of us loaded AA hulls beyond their useful life back when. I'd load them w/AA452 until there was almost no mouth left and what was, was both split & burned & they still broke correctly pointed skeet targets. No argument here about that.

Empirically, I observed that reloaded hulls using the Ljutic Mono Wads cut from some form of fiber board [I think] would grab the inside of previously fired AA hulls like they were super glued upon firing and stretch the hulls over 1/8" w/boring frequency. Those same loads almost always ironed any fold memory from the hull's mouth & when viewed from the side the hull's mouths were clearly stretched in a non-uniform manner. Some of them were off sounding on occasion as well, not always, but the hull stretching was. Same loads in a paper hull [Winchester, Federal or Remington] never exhibited that issue or sounded 'off'.

There was an article several years ago where someone had tested for pressure differences with differing crimp depths and found significant increases with increased crimp depth. I don't recall who wrote it or where it was published, but I remember it caused quite a stir at the time & I still see refs to that effect. Testing was done by an independent lab for the author. I do not believe there was much velocity dif. noted. and that it was done using once fired CF hulls.
Just saying.

Conventional 'card' wads? I'd not think they contribute anything significant to pressures generated.

If they are like the 20 gauge loads I just received, they appear to be made up with new Cheddite hulls with a star-type crimp. I have not fired any of mine. The boxes are marked, stating that the cartridges are loaded by Classic Shotshell/RST.

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.

Appears I was mistaken as to the type of crimp. Sounded like they were roll crimped but as per the photo they used a pie crimp. Why then use a roll crimp and heat to set it. Just belt and suspenders make the hull difficult to open and results in blown material at the hull mouth. Seems to me not a well thought out loading process. One or the other but not both!

I don't think I'd blame it on the gun.......a short chamber wouldn't do that to a hull.

Do I have enough information in this thread for anyone to say they would or would not continue shooting these loads?

I think you did a lot more homework than many would do. If I wanted an 8000psi load and discussed it with the manufacturer, I'd use them. I believe the manufacturers comment about the friction heat to set the crimp meant that the hull was weakened, not that the pressure was increased. Still, if that voice inside you says not to, then maybe use them up in a modern gun.

Will the MFG'er pressure test a couple of them, for your piece of mind? If you have a large qty. and the MFG;er won't, it may be worth it to you to send a couple to Tom A for private testing.

Just a thought.

I sent the MFG'er a picture. I didn't notice his response until just a few minutes ago even though he had responded two days ago. I get too much spam email.

He stated that they were over crimped and has offered to exchange. I'm just going to send them back so I don't have to worry.