Just a thought I shared with vz58 on his AR 17HMR project and reading about straight walled case adhesion here on this thread. I have an AMT 22MAG pistol that appears to be a staight blow back. The trick they used to "Retard" the action was to dimple the chamber so the case would stick a litte better until pressure dropped to delay cycle the action. Just food for thought. BTW... If you need some tungsten let me know as I have a few chunks some where (if I can find em) .