As a shooter and reloader for more than 40 years I'm stumped today with an issue. I just purchased a Cooper 52 Excalibur in a 6.5X284 Norma. The gun is used but looks as new. First shots down the tube and stuck case. After attempting several rounds I found Lapua new brass @ minimum load didn't stick but increase it by only one grain and brass sticks. 130 gr AccuBond with 49.5 grains H 4831SC sticks 48.5 grains OK. 140 gr Sierra HPBT 47 gr. H4831SC sticks 46 grains some OK and some stick. Tried Winchester brass and 140 gr Sierra with 45.5 gr. H4831SC sticks 45 grains OK Tried Retumbo and even with minimum load sticks brass. Tried 142 SMK, 140 VLD and 120 Nosler Bal. Tips all the brass sticks. I have two other 6.5's and have had three others and none of them have given me pressure problems until max. Any suggestions would be appreciated. The pressures great enough that you can't neck size the brass and get it to chamber must be full sized and then it's tight.