i would think that you still have a mismatch of ammo and rifle, especially if the de-resonator made a 1" difference.
My 24" heavy barrel loves 168 gr Fed GMM, Rem Prem 168 GMM, and Southwest Ammunition 168. I had my friend's 15 year old grandson shoot in Saturday at 100 yds. First time with a bolt gun. First shot was off, I got him to hold correctly, get the cant right, and not slap the trigger and he shot the next 4 rounds in under an inch. Yours should do the same when everything is right.
http://joelynch.smugmug.com/Friends/...EE505560-M.jpg
Joe