Boy, ain't that the truth. The last one I did, I drilled and tapped the hole, all went well, then countersunk, and could not get the tap started to clean the threads. I think this time I will drill, countersink, tap, in that order. Also, I think I will countersink a little deeper so the liner will go in a tad deeper, leaving a little more depth to the vent liner hole. The one I put in the last rifle I built, I did not countersink very deep leaving a thin touch hole, I put probably 600 round through the gun through the summer and the hole turned from a nice round 1/16" hole to a jagged, egg shaped hole, I countersunk the hole a little deeper and put a new liner in. I am assuming I just did not countersink deep enough. chuck