To me, the action is a component in the overall build. It in itself may not make you a sub half moa shooter, but I have several factory rifles that shoot pretty well, in the .75 moa area, occasionally spitting out a sub half moa group. Sometimes you have to wonder when you shoot the bigger groups how much role you played in the bigger group. I have one full on custom build based on a Defiance action, and Bartlein barrel. If you shoot a group with that that's approaching 1/2 moa, or over half moa, it was your fault. No question. Hands down the most accurate rifle I've ever held. A custom can help you advance your skills, but then again so can having a smith just fit a custom barrel on a factory action, bedding, and floating it. The action may add a little more accuracy to that. Question is, is it worth the money? To me it was, just to have a rifle that was "perfect" and I never had to question if I hurt its performance by not using top shelf components.