I load cast bullets almost exclusively for my 1911's. I check all my cases for length before loading, simply set a dial caliper to max length or a hair less, and if the case slides through the jaws, it's good to go. I have so much brass, I just scrap any that are too long. I use a RCBS taper crimp die, and simply adjust the die down until the rounds meet the described above "plunk test". I have two dies, one I leave set for jacketed bullets, one for cast. This should solve the problem, unless as stated before, your relatively heavy 250 grain bullets are fairly straight sided, and the leade in the rifling is to short or steeply angled to clear the nose at your seating depth. I mostly use bullets cast from an old NEI 230gr round nose mold, or a 200gr RCBS semi wadcutter.