Was having trouble getting under 1.5 inch groups at 20 yards with my Gen 1 marauder until I purchased a tin of H&N Field Target Trophy in 5.54 head size. Now I'm down to 1/2 inch at the same distance.
dark I have Gen2 in 22 & 25 cal. the 22 I use the crosman dome 14.3 good results- crosman hollow pt.14.3 suck- jsb 18.1 about the same as crosman dome 14.3 at 44 yds gets me 3/8 to 1/2 groups . The 25 cal. I shoot jsb's 25.4 for about the same results at 44 yds. Plan on tinkering with them this summer just to many toys & hobbies . Best of luck Darell