Sound advise from Joel: Work out the variables.
Try 250 gr Shockwaves with 2-50 gr pellets of 777 for a possible effective bullet/charge combo. They align to the Omega's well but I never shot a triumph. You may be flinching if shooting at 150 gr.
Let the barrel cool before shots. Swab with barrel with a wet and dry patch. Do not count the first shot assuming your barrel is squeky clean as that may be a flyer.