Flat and sharp edged bases are nice to have but I have also found uniformed hand beveled bases to be a bit more consistent for me. Everyone has a different approach and which ever one works out to be the best for you is indeed the one you should use.

JLouis

CW the sprue cut off needs to be sharp and the plate flat. The later not being typically what I have found on most new moulds so I generally have to hand lap them flat on a thick piece of flat glass. This also leaves a very sharp cutting edge once the plate is lapped perfectly flat. I have also found the sprue plate hole size to also be a bit important and if to large it will push lead to the edge of the bases and not cleanly cut the sprue off. If to small the bases don't want to completely fill out so there is a bit of a fine line to find just the right combination based on the bullet size. Having the spare cut off centered in the bullet I have also found to be very helpful. The ultimate goal for me is to try and achieve a perfectly balanced bullet and if one pushes lead towards the edge of the base when cutting off the sprue or inducing air pockets by using pour casting practices being even the more typical it just isn't going to happen. 

JLouis

All my casting molds have the sprue plate adjusted so when the mold is 'flipped' holding the handles, the plate swings open freely.  Then when casting, after a 5 second pour count, I cut the sprue with downward pressure on the plate on the top of mold halves = nice flat bullet bases

Thanks JoeB if the sprue plate is lapped flat and adjusted correctly there is not need for whacking the bases flat. Actually it can be a bit hard on the alignment pin holes and while on the subject the pins are not always adjusted correctly on a new mould and something else one should always check. And periodically as the holes continue to wear from use. 

JLouis

JLouis wrote on Jun 22^nd, 2018 at 1:14pm:


Hmmm.  I had a friend (in the metrology lab) measure the flatness (with a CMM) of 5 or 6 sprue plates (new) that I had - all were within .001 or a LITTLE more of being flat.  (Just did it for a point of reference.)

JLouis wrote on Jun 22^nd, 2018 at 9:47pm:


These were two cavity Lyman.  Bought as a group from someone many years back.  No wear on them - looked new.

I use high heat oven gloves inside XL leather gloves.

This allows me to handle the hot shear plate without getting burned.

When I first started I whacked the sprue plate with a wood dowel as I was advised by the experts of the day.
After about 50,000 rounds I had pounded the lock pin holes so loose the bullet was coming .007`out of round.
No more whacking of my moulds and they last forever.