1. Mix chili sauce, lime juice, fish sauce, and cilantro; set aside.
2. Divide shrimp into 4 equal portions. Lay each portion of shrimp in a neat row with tails pointed in the same direction. Thread 2 thin wood or metal skewers (8 to 10 in. long) about 1 1/2 inches apart through center of each row of shrimp, pushing the shellfish close together.
3. Place shrimp on an oiled grill above a solid bed of hot coals or high heat on a gas barbecue (you can hold your hand at grill level only 2 to 3 seconds); close lid on gas grill.
4. Cook, turning once, until shrimp are pink, 2 to 3 minutes a side.
5. Brush tops of shrimp with the chili sauce mixture, turn over, and cook just until glaze bubbles and browns slightly, about 30 seconds (watch closely; glaze burns easily). Brush tops with more chili mixture, then turn glaze down and cook just until it darkens slightly, about 30 seconds more.
6. Transfer shrimp to plates or a platter. Season to taste with remaining chili mixture and juice from lime wedges.