This Mark IV replaces a small, lightweight semi-auto I recently sold. The differences (weight, sight radius, recoil etc.) are significant. I'll be trying different types of 22 ammo to see which ones I may avoid. So far the the inexpensive Golden Bullets are fine. As for modifications I've only made 2 so far. A rubber, finger grooved Hogue grips which I like and I painted, with red nail polish, the front sight...which helps a lot. As for upgrading the ejector, any springs or firing pin I'll wait to see if I have any failures to feed or eject and light strikes. The trigger seems fine to me. After several outings I'll use some CCI Minimags to check the groupings. For now it's fun to shoot at a hanging 8" steel gong & 3" steel spinner about 30 yards away.