Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the rear sight type on the model with the acr muzzle brake device?

### Inputs:
table_name: table, columns: ['Colt model no.', 'Military designation', 'Barrel Length', 'Barrel', 'Handguard type', 'Buttstock type', 'Pistol grip type', 'Lower receiver type', 'Upper receiver type', 'Rear sight type', 'Front sight type', 'Muzzle device', 'Forward assist?', 'Case deflector?', 'Bayonet lug?', 'Trigger pack']

### Response:
SELECT Rear sight type FROM table WHERE Muzzle device = ACR muzzle brake