Table: ar15_variants_5
Columns: colt_model_no
name
stock
fire_control
rear_sight
forward_assist
case_deflector
barrel_length
barrel_profile
barrel_twist
hand_guards
bayonet_lug
muzzle_device

Question: What is the muzzle device with a 1:7 barrel twist and a stock 4th generation?
SQL: SELECT "muzzle_device" FROM ar15_variants_5 WHERE "barrel_twist" = '1:7' AND "stock" = '4th generation'