On my fatty forearms I used 1" 6/32 stainless Allen head grubs...good luck
Heres what she looks like with the 18 in barrel,stock screw on and crosman 760 sights.I never liked the rear site options,the 760 sights arent blured because its further away from you.I also machined my bolt prob to be longer,a common problem is the pellets skirt is covering half of the air hole,some will arguee that its fine.....i figure it wouldnt hurt to push the pellet 1/16 further in.All internals and pump parts are stock.