Casting some boolits today and all of a sudden I could not get the sprue plate to cut the sprues. Poured over 300 boolits and all was great . From one pour to the next I had to hammer like hell to get the plate to cut. It was only a matter of a few seconds of the pour cooling at the same cadence i used the whole pot. Checked the sprue plate and it appeared to be fine. Not warped and no gap under it indicating it was bent. Empty the spue plate rotated easily but as soon as I made ap pour it locked up. In all my years of casting I never had this happen and cannot figure out what is causing it. Put a little more sprue plate lube on and it made no difference. Stumped ..... HELP