Good calculations azdukhuntr. Was looking for Herters info or crimp sealant info, not a BPI data discussion myself, as I don't have any data to even have that discussion. I'll get the loads tested, and will also replicate them without the crimp sealant for testing-- that should give a good data point on what sealant can do. I lean away from maligning the data until I have real tested info... This incident spurs me to look at this one specific load more deeply. LilGun is a slow powder, with data posted by Hodgdon for 28 and 410 lead loads only; this is more indicative of the sparsity of Hodgdon load data than an indictment of the powder's use in 20ga however, as they don't even post ANY 20ga steel or heavier-than-lead data at all! Concluding lilgun is inappropriate for 20ga use from that is no more reasonable than concluding steel shot or HeviShot from a 20ga is dangerous-- it's false logic. In most 20, 16, and 28ga hulls Hodgdon has only gone to the effort of testing one or two powders.
BT, I posted this thread precisely to GATHER DATA before I jumped to conclusions without data. My OP gives my two big areas of suspicion, crimp sealant and Herter's hulls. Your thoughts on seriously downloading this powder charge are what my plans are also; I actually avoided LONGSHOT and prioritized the LilGun HW loads due to OTHER threads that cast fear or doubt upon Longshot for steel. None of that should apply to denser HW loading, but I was being cautious anyways. Unfortunately there is almost zero data in existence for 20ga HW, so I can't disregard all BPI data-- it's all there is for 20ga if you're not doing lead.
I've posted a couple questions before on crimp sealant pressure, and while there are a lot of folks with opinions on what to use there is really no data posted on tested loads where the only difference is a sealed crimp-- at least in all the threads I've found. BT asked me what I thought was happening; I don't have enough info for an opinion, so I'll rather say "I'm investigating two areas that I most think bear scrutiny here". First, I do believe that the crimp sealant delayed crimp opening-- the off-center open mouth of the hull seems to indicate that. Looks like the load squirted out just one side of the open crimp or something. I didn't take a picture of the mouth, wish I had as I knew I was going to post here on it, but was in the field for 3 days and don't know what I did with the dang hull now. I begin to think a pic of the mouth might give folks more info than the end I photographed. That would cause the symptoms I saw I think-- front of hull driven forward into the forcing cone due to mouth not opening fully, and "ripping" the whole hull away from the basewad. It was then "stuck" in there by being too far into the chamber, past it really.
The second thing i suspect is that Herters, the "promo" load for Cabelas, are very cheaply made, and maybe not as strong as some other cheddite hulls. I base this on having had this same sort of original skeet shell have 'ripped' brass head by the ejector when shooting 7/8oz loads, as if the metal head is very thin and weak-- yet I shoot boxes the same day of Rem GC and don't have any issues. I looked at some once fired Herters hulls or the sort I used for this load, just a 7/8oz skeet target load from Cabelas, and many have an extractor groove "bump" on the bottom-- the sort of thing you'd look for as an over-pressure sign on metallic reloading. Of course an 1150ish skeet shell shouldn't have pressure issues, which makes me suspect the hull metal head is weaker/thinner than some hulls. Thickness is a saami spec that must be close for hulls to chamber and bolts to lock-up, so I would more suspect a weak alloy; I could maybe do some "bend testing" on the heads using weights to compare to other hulls. I have a couple threads on SGW about 20ga Herters issues including 2 incidents of commercial skeet loads having heads ripped and one of the basewad separating and being partway up the hull-- all in the first box I ever shot of it at the range. Win SX3 20ga, perfect function on 700 rounds or so of GC right after-- no gun issues I'm saying. I threw all of the hulls away and didn't plan on using it for reloads, but then I NEEDED some cheddite hulls for this load, so I used some despite my earlier misgivings.
As far as "cross checking" the data, I looked at every single data point out there, and had sufficient info to load it, I thought.
2.75" cheddite 20ga hull; ch209 primer; 7/8oz ITX13. 42gr LilGun= 10,400psi with HS12 shot, 42.5= 11,500psi with ITX13; 43gr = 9600psi in a Rio/Rio209 combo with ITX13. There was a lengthy article written about the 42.5gr load and it's field use by Curmudgeon, which gave me confidence that it was surely a truly tested load. The 3/4oz loads had 46gr and gave 9000psi, which seemed in line. DESPITE all that, I dropped the powder 1.5gr. So I think I did my due diligence on this.
My theory is that crimp sealant can cause significantly more pressure increases than anyone talks about, and rather than pointing the finger at BPI data I would FIRST put forward the (equally untested) theory that gluing crimps shut with any form of sealant can result in pressure spikes. It's self-evident that it SHOULD, and it's an un-talked of area or at least insufficiently researched area-- discussion with zero data abounds, and folks are quick to dismiss it. The only data I have EVER come across was Tom Roster doing a test to see what different crimp DEPTH did to pressure, and it was significant... if mere crimp depth can delay opening long enough to seriously increase pressure (I remember several thousand psi difference maybe?), then some form of sealant/glue should surely be suspect.