Help my Grendel pistol isn’t accurate

[Zeneffect]

I was going to just buy the shims, then I totaled what I wanted and yea. I have amazon prime so next day a set of feeler gauges I would cut up as stainless shim stock was in hand. A strip of tape covering the desired shim taped to a 2x4 and a drill to get the holes, scissors to cut to size. Whack it flat and install. Cost $6 total and only took 5 min to make using simple tools.