HC-SR04 ultrasonic sensor reading issues

Hello everyone! I am trying to use an HC-SR04 ultrasonic sensor with the newping library. The problem I am having is that when a distance I am trying to measure is more than 12cm, the reading I get is 12cm. I have the maximum distance set to 400, and if the object is closer than 12cm, the reading is correct. This is stressing me out because I have tried more than one HC-SR04, bot from different manufacturers, and still no success. I have a 50ms delay between pings, but no matter what I change this to, it does not work. Any suggestions?