Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_19901_1 (rear_sight_type VARCHAR, muzzle_device VARCHAR)
### Question:
What is the rear sight type on the model with the acr muzzle brake device? 
### Answer:
SELECT rear_sight_type FROM table_19901_1 WHERE muzzle_device = "ACR muzzle brake"