Farming a specific weapon in trials, let alone with a specific roll, is an awful frustrating and lengthy task with all weapons and even the armor being in the pool all the time. Getting the weapon you want statistically only every 10th match is absolutely no fun and as w/o the luxury of being 450 and constantly getting 3 perks per row the chance of at least one desired combo is 4/49. So overall we are talking of appr. 0,8% of a "useful" drop and over 99% trash....