Just got in from shooting a 336 RC, 35 Remington, that I bought used. Shooting 150 grainers at 50 yds. holes in the target were almost perfect. Using Winchester and Remington 200 grainers....both tumbled and keyholed at 50 yds and 100 yds. Slashes were about an inch and a half long. I returned the rifle to the place that I bought it and they had me leave it for the gunsmith, along with the four targets and two samples of the 200 grain bullets used. The bore is clean and the micro grooves still have a great deal of depth. The crown is good. It looks like the action might be feeding the 200 grain bullets in too far so that they touch the lands. The 150s are more pointed; the 200s are round nosed. The two sales fellows, both knowledgeable, want the gunsmith to look at it, using fingernail polish to see how far it feeds into the bore and if it is touching the lands, and said, there is an adjustment on the Marlin 336's that can correct the amount of feeding that takes place. Anyone with any experience on that end know of this happening before, or having adjusted the action in their own gun to correct such a problem? or what causes a bullet to tumble?? Thanks.