Wont stay in place - J&E Machine Tech AR-15 Mil-Spec Gen III SOPMOD Buttstock

When i first got it, it felt great in the shoulder pocket and comfortable on the cheek positioning. Then weeks later i had to shoot a qualification labe with my M4. The buttstock says Milspec and fit the the military M4 buffer tube well. Then it came doen to shooting the qual and the stock kept coming out of position and slamming into the reciever. I had to take my support hand off and try my best to hold it inplace! After failing two quals, i gave up and borrowed my friends buttstock to qualify and finish up the day. It was very frustrating and shooting was too laborous than it needed to be. Definitely not fit for combat nor competition. Looks good, so if you have a wall piece type of carbine, then buy it. Thats all its good for at this point.