I been down this road when i built mine. The factory takedown screw is set at around 20"lbs (inch pounds, not foot pounds). It is recommend that when you build it to tighten the take down screw to 15-25"lbs. Start at 15 then shoot and observe and tighten till your grouping tightens up mine seemed to like 22"lbs. Now for the v-block they recomend tightening them to 20-25"lbs also. Remember you are screwing a fine threaded steel screw into aluminum so dont overtighten. Hope this helps