Powder Ignition Failure

[Bruce_in_Oz]

Many years ago I was warned about "low" loads in pistol cases.

The one that got a bit of publicity in pistol-shooting circles was:

2.7 grains of "Bullseye" behind a 148gn Wadcutter in a .38spl case. This was reputed to potentially take your nice K-38 apart without a screwdriver.

I recall that the H. P. White lab had done some looking into this matter.

Bullseye is one of the fastest powders ever offered on the commercial market and was designed for light loads in small cases.

2.7 grains of the stuff barely forms a film on the bottom of the case. A "flashover" means that the whole lot ignites ALMOST instantaneously, as opposed to damn fast. Explosion vs. VERY rapid burn. The resultant SHOCK is what makes your K-38 look shabby.

"Low" loads mean that there is a lot of space NOT occupied by the propellant. Variations on how the propellant is "arranged" at each shot will lead to variations in ignition and thus pressure curve, and, ultimately, down-range performance.

This applies at ALL variations of "partly full", but is MUCH less noticeable as "full" density is approached.

Some years ago I was fooling around with some .223 Rem loads and getting odd pressure signs but reasonable accuracy. A mate was over one day and I raised the matter. He looked at me "funny" and said he was using the same cases, powder and bullet as I was, BUT using MORE of the same powder, in fact, a slightly compressed load. I gave it a whirl and he was right; one grain more than my most recent trial produced smaller groups AND did not display the serious primer flattening of the marginally "lighter" loads. Voodoo stuff indeed.