Hello, I have a tikka t3 in 7 rem mag I bought used. It shoot terrible. I tried 5 different factory options and even reloaded for it. So I bought a take off barrel from a forum. I took of the old barrel . And threaded the new one on and it doesn’t head space. I was under the impression that the barrels were interchangeable and that’s why people can offer a pre fit shouldered barrel. What am I missing. Is there a difference between the t3 and the t3x as far as this is concerned?