Secondary Explosion Effect using cast Bullets

[Taglialenha]

What you think about the secondary explosion effect? Legend or something to worry about? Any advice?

[Veral]

  I wouldn't say legend is the right word, nor is fable.   Feeble attempt at making a lawsuit of of a double charge would be most correct discription.  But it doesn't work, as no attorney will even look at a suit if reloads are involved, nor will any court entertain one.  All reloading suits are thrown out of court as soon as it is proven that reloads are involved.

  In all the claimed cases  of 'secondary explosion' that I've heard of, the shooter was using a charge that took up less than half the powder space.  The powder which is most cursed for this claimed effect is 296, which just happens to be the most popular and accurate powder used by schutzen shooters, so Win recommends not using it for cast rifle loads, but Hodgen sells the same powder with no such warning.
 
  I've played with quite a bit of it in light loads and could find no way to even get velocity excursions, let along pressure problems.

  I once split the cylinder on a Ruger 44 blackhawk when I was shooting less than half a case of bullseye.  My own brother watched be trip in two charges but had no idea that I had made a mistake till I pulled the trigger and got a monstrously increased dose of recoil and smoke!  As I was stuttering around trying to figgure out what had gone wrong, and believeing perhaps it was a secondary explosion I checked a case to see if it would hold two charges, and it did.  As I pondered that situation out load, my brother said he watched me do it but thought I knew what I was doing.             It's an awful embarassing situation, and dangerous, and many people who do it in public try to find someone else to blame and pay the bill for them.   

  I've never used a stout load since if the case will hold two charges of it, and that's what I recommend to everyone when this subject comes up.  If the load is very light and doubling the charge still isn't over pressure, I might use such a load, but prefer not.  If I double trip the powder measure, I prefer to be surprised by not being able to seat a bullet, or seing powder spill off the case, than with a huge bang and smoke coming out of the gun everywhere!

[docmagnum357]

ditto.  I once double charged a 44 mag with unique.  12 grains was max, I was using 9, and i doubled it to 18.  did n't rupture the cylinder, but it bulged a chamber, ruining a 1958 model, pre 29 44 mag.  Be careful.

[Terbltim]

I've heard of this and read a lot about it.
The US Army Artillery Corps knows [and has written] a lot about the phenomenon of "detonation" from light loads.
The message I get from it all is don't let it happen to you!
At the other end, the possibility of double-charging keeps me thinking that it is wise to use a policy wherein I do not use any powder/load combination that uses less than about 60% of available volume.
Commercial manufacturers (it is claimed) hold to a 2/3-full dictum for most loads...sometimes more but never less. (I don't know if this is true but it sure makes sense.)
My opinion, for what its worth, is that if your powder doesn't take up at least a bit more than half the available space behind the bullet, you are using the wrong powder.
Following that thinking, I try to use a powder that will fill as much of the available space as I can while giving me the velocity/performance I'm looking for.
I think powders like Bullseye, R-1, Red Dot and others of that ilk are for teensy-weensy case capacities. I don't reload for such ammo so I don't use those types of powder...for anything, and don't keep any around.
Filling more of the available space seems to give more consistent performance than using less of the space. That has been how it worked out for me without exception.
I agree totally with Veral in that if I double-charge a case I want an instant mess to be the result or at least not be able to seat the bullet to correct depth.
That practice solves the problem before it happens.