A clam gun is a traditional muzzle-loading firearm, kind of a cross between a shotgun and a rifle, usually about 68 caliber or so, that is used in a two step process. First, a line of clam-gunners, known as the 'Blasters', form up line abreast before a likely clam-bearing area. Upon a signal from the leader of the hunt, the 'Master Blaster', each gun is fired in sequence, each successive blast being timed with the ebb of each ocean wave. If all goes well, the experience and skill of the Master Blaster being most important, the clams will stampede toward the second line of hunters, the 'Whumpers'.
Unlike the Blasters, the Whumpers' clam guns are charged with shot, a special blend of flour, corn meal and special spices, the recipes of which are usually closely guarded family secrets. Upon seeing evidence of a stampeding clam, normally a slight, moving mound, the alert Whumper will fire directly into the sand, leading the disturbance ever so slightly. (According to some authorities, the sound of the shot impacting the sand is the source of the Whumper's title.) An experienced Whumper will not only cleanly kill the clam, preventing any undue suffering, but the charge of flour and spices will prepare it for cooking.
There is considerable controversy and jealousy between traditional clam gunners, those described above, and the Modernists, who use a plastic or aluminum tube, approximately 6 inches in diameter with a T handle and small air hole in the top. The Modernists identifies a likely clam location by spying a depression in the sand and works the hollow tube down almost to the handle. Then, by covering the vent hole with a finger, the tube is pulled out with a "core sample" of sand that, hopefully, contains the clam.
I like the Traditionalist way a lot better.