The .303 experiment continues

While back I wrote about trying to make cast bullets come out a bit larger by putting some aluminum tape on the faces of the blocks.  It works, but does make the bullets out-of-round by a bit; no way around it when you do something of the sort.  So.

The ideal way to get larger-diameter bullets is to go to someone who makes molds and have them make one with larger cavities, or find someone who makes such and buy the mold.  Can you say 'spendy'?  Either of those not really in the cards right now, so decided to try something else: enlarging the cavities on the mold I have by lapping them out with abrasives.

Decided to try this because it's a Lee mold.  That means two things:
The blocks are aluminum, so figured wouldn't require a horrible amount of work to lap out the cavities, and
If I screwed it up, you can replace this mold for around $20, as opposed to a Lyman or RCBS or something which runs ~$80.

So, take your mold.

Take some bullets as-cast.

Drill a hole into the base of a few so you can screw a machine screw in for a shank(try real hard to get it centered). 

Coat bullet with valve-grinding compound.  Place carefully in mold cavity and start turning.  Take out and add more compound as needed, and reverse the direction occasionally

When you think you've (hopefully) enlarged it a bit, do the same to the other cavity.  You'll need to replace bullets anywhere from once to several times, depending on how much you want to lap the cavities out.

When you think you're done, clean out the cavities, then use something like Flitz or Wenol polish on some bullets to really smooth the surfaces.

Then clean the blocks THOROUGHLY, every trace of the abrasives, then try casting some bullets to see how you did.

I had to do the whole routine a second time, first time didn't enlarge the cavities enough.  Second time seemed to do the job: the bullets originally came out right at .311", now they're about .314-315. 

I loaded ten with the standard 16.0 of 2400 practice loads, and tried them this morning at 30 yards.

The 'front' and 'rear' notes which cavity that set came from.  Don't know from the one test if the front came out better, or I just spread them a bit on the second group.  

 Not bad at all, especially considering I was shooting them.  I'll load some more for next time can get to the outdoor range with solid benches and longer distances to cut down on the error factors.