Cherry-cut molds are potentially a bit more out of round than lathe bored.  However, 3-4 thou is probably beyond what would be considered acceptable.  Get a good magnifier and examine mold faces for minute burrs or debris that might be preventing complete closure.  Putting a sheet of 400 grit wet/dry paper on a piece of plate glass with careful work will remove slightly raised areas along the edges of the cavity and dowel holes if they're present.  Dowel pins can have protrusion adjusted so that the mold releases easily but there is NO diagonal play between the faces.  If the faces check out perfectly clean and flat, then the variation exists within the cavity itself, and there may be little that can be done other than using the blocks as a "blank" to lathe-cut a larger caliber bullet.
  
Whether a .003" variation will make a noticeable difference in accuracy (assuming bullets will be sized before shooting) MAY not matter if you're not at the top of the competitive game with a caliber as large as .45.  But it does increase the pressure it takes to press the bullet through the die, and with a 1:40 alloy, increased sizing effort increases the chances for distortion of the bullet,especially with a long unsupported nose like the Postell. 

Just a few thoughts...

Oh, and welcome aboard!!

  Let me join with John in PA in Welcoming you to the A.S.S.R.A. Forum.  The added attraction for me is that you are the proud owner of a CPA/Stevens actioned rifle.  The CPA's are really great, aren't they.

Hobbs-Pal (did I get that right?), Just a couple of comments for your consideration.  I realize that your first bullet casting session was at your friend's location, using his equipment; but when you get ready to set-up your own casting arrangements, consider this.

I have found that large size furnaces, pots and ladles are more of a hindrance than they are a benefit.  A 75 pound pot of lead is more like what an old time plumber would use for poured joints with cast iron pipe.  Even if you were to be casting 500 grain .45 cal Gov't bullets, a smaller pot is better.  there are 7,000 grains to the pound, so you will get approximately 14 such bullets to the pound of lead.

I decided a long time ago that I would put less lead down range when shooting paper.

My second point is to purchase the best customer bullet mould that you budget will accommodate , for your second mould.  Get your first mould at the least amount of cost to you.  Use the first mould to "introduce you to the sport, the caliber, the rifle, etc., etc.  Your initial investment into BPCR shooting has been made, i.e., your CPA rifle.  Now experiment with different style nose bullets and different weight bullets.  Your are striving for accuracy, so don't rush out and expedite the process.  The process takes time, so give it time and make decisions as you progress.  When trial and error have shown you the way for your rifle; then purchase your second mould from a custom (big name) maker.

Good luck and keep us posted,

Creedmoormatch in PA
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thanks so much for the welcome and good advice.  i've never shot a gun before (one clip through an m1 in navy boot camp) so this is all really new.  my friend has a LOT of experience.  boy, i'll tell you that 8 " dot looks really tiny at 200 yards through the peep.

we're going to re-test hardness and go from there with a 750-770 temp.

Old-Win wrote on May 26^th, 2013 at 5:54pm:

Amen to this advice.
Our 2-piece stocks/rifles are very much more susceptible to accuracy problems when holding the gun differently shot-to-shot. Try to find a comfortable position and hold the rifle exactly the same on each shot. If you change your hold in any way the shot will show it. BPCR shooting requires great consistency. Something I'm just starting to achieve. as I get into my 2nd full season of silhouettes.

If you want to use a lubrisizer just to lube bullets get a sizing die that's .001" over the bullet diameter as cast.

Well said Cary.  Shoot a few bullets that you have cast.
See what happens. Then with a little experience, go for a better mould, etc.
Kurt

Your experiences mirror my own starting with this hobby, Im a machinist also, me and one of the shops welders play with the 45-70 except I use a shiloh and he shoots a Remington.

First thing you should do is try some out bullets, just do a plain pan lube and work up a suitable load, reloader 7 has been kind to me and lately plain old black powder never dissapoints.

Next step is taking a read of this, read about "Beagling" a mould. (You need to Login or Register to view media files and links)

While I like the postell, the lyman 500 grain roundnose is my personal favourite, Im going to eventually try the pointy shmitzer bullet next.   

Enjoy the time out, take your time and any day out shooting is a good one.  Remember that as you learn to load an accurate cartridge.