Note: It was not a 155mm artillery shell explosion, only the fuse of a 155mm artillery shell. One has about 15 lbs of TNT, the other a “booster” pellet to initiate the explosion of the main charge.
The booster pellet is much less than an ounce, I believe.
Perhaps someone else can give the exact weight of the booste pellet.
It is the difference between a primer and the main charge in a rifle cartridge.