There are many little gimmick slugs out there. One of them is a hollow lead shell with a hole for a Winchester 208 shotgun primer in the top. It is meant to be filled with black powder and then fired. When the primer hits a solid surface you get a small explosion and a flash.
Theoretically the .22 blank works like a big primer with a greatly reduced ability to ignite powder or gasoline or whatever.
When I was in college I hollowed out a few .44 mag hydra-shok HPs (pulled the pin and worked some of the lead out with a dremel) , put as much smokeless powder as I could in the cavity and capped it all with a reversed magnum pistol primer. I shellaqued the thing in place with clear nail polish (girlfriend's..not mine
) and shot them out of a Model 29. They made a little pop and a flash when they hit solid objects. Some primitive test made it look like the rounds were expanding VERY rapidly, like to over 1 inch in diameter in less than 2 inches of wet phonebook. But I was a very biased observeer hoping that the explosion would cause rapid expansion.
The theory behind most "exploding" small arm rounds is obviously not to cuase concussion damage (too small of a delivery package), but to throw small shrapnel and cause rapid expansion.
AS I understand it, the construction of such devices could be considered bomb building. So be careful, both practically and legally. I recomend that people stay away from such experiments....
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-Essayons