Turn on a gas grill to medium-high, about 400°F.

Devein the shrimp. Secure the shrimp on metal skewers at least 12 inches long by piercing them twice, first through the body and then through the tail section, forming a C shape. Don't overload any one skewer.

Place the butter in a 2-cup glass measure and microwave, uncovered, on high, until almost melted, about 30 seconds. Whisk in the mustard until well blended. Brush both sides of the skewered shrimp with the sauce and grill, uncovered, until just pink on the first side, about 2 minutes. Turn and continue to grill just until the shrimp turn pink on the second side, about 2 minutes more. Do not overcook.

Remove the shrimp from the skewers and serve. This shrimp is good served over a bed of hot cooked rice.