"Double-barrel buck shot" is actually mixing 2 related terms. "Double-barrel" is any gun using two barrels; they can be "over-under" or side-by-side. Here Beck is referring to a shotgun, because he follows that by saying "buck shot" which, btw, is generally written "buckshot" (one word). Shotgun shells are generally filled with small pellets that spread out after they leave the barrel. Buckshot is larger, heavy pellets used for home defense or hunting large game - like a "buck," which is a male deer. Hence the name.

Running for exercise and picking up trash you find along the way. It's good for the body, mind, soul, and environment! Started in Sweden but is making its way to the U. S.