Supposed to be mil-spec? - XTS AR Shock Abosrbing Stock

I have a Stag Arms AR which has a Mil-Spec buffer tube. I tried to put this stock on and it was incredibly tight. I thought hmmm maybe it once it gets past the first few inches it will fit better. No such luck. I had pushed the stock down onto my buffer tube and the thing was stuck...not like just give it an extra little bit stuck either. To get the thing off I had to tie the sling to one end of the stock and another sling to the magazine tube and loop it around my foot and pull with everything I to remove it...and it still took hitting it with a hammer to get it to come off. So now I am stuck with a stock I cant use and a weapon I can't use until I order me a new stock.