Here are links to the other 2 threads on The Exploding Taurus. I hope that some may find this entire saga useful in the future
http://castboolits.gunloads.com/show...loads-Opinions
http://castboolits.gunloads.com/show...e-Found-So-Far
The other 2 threads were full of useful insights and suggestions. Many guys stepped up to the plate including through PM's and the last PM started me thinking. Combined with some of the other comments, research on this sight and a link to a different site about velocity vs barrel length caused everything to click so here it is.
I first started out looking at the ammo and then the components. I checked that the powder was correct and because of a suggestion that the wrong powder may have been put into the bottle I was using, poured the bottle out and compared to the ETR7 I last used to load up some 38sp. All was the normal black Unique. After several suggested a double load I weighed all of the rounds and they were within a couple of grains of each other and with my hand trickling each round and using a single stage there was at least 3 times I looked into the brass and would have noticed a double as I tried loading 17.6gr of Unique in one to see what it looked like and it was near the rim easily visible. I would have caught it. Another suggested checking the scale to see if I'd moved it somehow from grains to grams as my GemPro 250 has grams, grains, ounces, carots and probably British Stones. I checked it then re calibrated it before pulling bullets and weighing the powder of a random selection of bullets. All was where it should be within .05grains. Another member suggested bullet setback so I checked the bullets and they all looked good. When I ran some over a chrony yesterday after each shot I opened the BH up to look at them and they were fine. Dismissing that I turned to the revolver and looked at everything I could think of and what members suggested. The barrel was fine showing little leading, no Glock Block, bulge or anything although the forcing cone was tilted a little down and to about 1900 with some lead jammed into the area between the cone and the frame which I didn't notice the first time around as I assumed it was powder until I scraped it with a pick and it came up shiny.
Someone pointed to the cylinder itself and a pressure spike caused by ??. Also suggested was either a manufacturers defect in the metal or a flat out blockage in the chamber evidenced by the position of the bulge in the cylinder. Even a loose boolit was brought up. Further in the thread someone said something about the cylinder free wheeling or being off and I found a different site that said this was not unknown in Taurus pistols so I checked again and sure enough the round that was in the chamber that blew had a slightly off center firing pin strike. The final clues were my reading an old thread about Unique with a mention from Larry Gibson that as you approach max with Unique it can get spikey. This was followed by an article sent to me by a friend not on this site about barrel length testing in relation to differences in velocity readings. Unrelated to this discussion but timely.
All of this brings me to yesterday's testing of 20 random rounds from the box of 100 reloads. I was looking for velocity spikes indicating pressure changes but came up with a deviation that was not out of the norm. I assumed that since I was using a BH with a 7.5in barrel instead of the 6.5in of the Taurus combined with a tighter cylinder gap the velocity would be higher. The readings I got averaged 1065fps with one at 1100fps. For some reason that didn't register as I was concerned with variation not the numbers themselves. When I got to thinking about it today I remembered I should have been in the 900fps range. That didn't sound right. When I got home I checked the book to make sure and after re-reading the article on barrel length realized that each inch of barrel should have been about a change of 25fps and here I was 200fps over. When I tested a few the first time I didn't use a chrony, I just shot a couple and they were fine so loaded them up. The extra FPS could not be explained by the barrel length, cylinder gap, slight powder difference or the difference in weight of the cast boolits. Not that much so I pulled the ammo out when I got home and looked at it again.
All looked good with a nice, heavy crimp but when I pulled out my RCBS Dial Caliper to measure them something was off. I had visually looked at them but not measured them. The lengths were a uniform 1.565in. Huh? They should have been 1.60in. What gives? Thinking back I had not used my RCBS Dial but a Franklin Armory Digital I had for several years. Getting it out and trying gave me....1.6in. Several attempts at measuring bullets, ammo and a few other things showed it consistently off.
So, long story short here is my theory based on all of this. All of the ammo had the bullet too far into the case to start due to the faulty digital caliper. Being near max loading this had the effect of raising the already high pressure to near the limit for the Judge. When firing that light gun each round had enough recoil to force the rim of the brass on the next round a tiny bit into the lead itself in the crimp groove forcing the bullet a little farther into the case raising the pressure a little more. By the third round the recoil forced the cylinder to come a little loose evidenced by the just off center firing pin strike and the leading at the top right of the cone from the 4th bullet glancing it on the way down and out the barrel. At the third round the pressure may have even been enough to weaken or crack the cylinder wall between it and the 4th round. When the hammer dropped on the fourth and final round the bullet had been forced just enough into the casing to reach the critical point and the powder pressure spiked over the safe limit for the Taurus. Not enough to damage the far stronger Blackhawk but in excess of what the Taurus was designed for. This caused the cylinder to blow up and the top strap to come off. How the brass didn't get destroyed is a mystery in itself but stranger things have happened.
Too short rounds caused by a faulty caliper + light gun + spiky pressure + bullet setback just over the critical level = BOOM.
These rounds would be safe to shoot and I did shoot 20 or so in my BH with no problem. The Taurus Judge is not made for that or is a dedicated 45lc so is not the best to be shooting these rounds in the first place let alone top end even if they are within book.
How to not have this happen again:
In a gun not dedicated to 45LC like a Taurus Judge or a lesser gun than a BH, RH etc do not approach max loadings.
Check equipment for proper function before using the ammo. I threw out the digital caliper and am ordering a much nicer dial to back up the old RCBS Dial.
Use a Chronograph to check newly loaded rounds especially if you either have not tried that loading before and doubly so if approaching max.
Pay attention to the velocity itself and not just spikes or erratic readings.
All right, long winded but I think this is a plausible explanation based on the input from the members here and some research on my own part. Any Comments on this????