since they are lathe cut I assume you could get two completely different bullets in a double.  Personally I think I'd keep them about the same volume though to avoid casting temp variations. 
  I have had several doubles made, one is truly a duplicate, within his CNC machining tolerance range, and they are so close I no longer bother segregating the bullets.
  Another is where I was trying different lube groove patterns on the same bullet to see if there was a difference  (if there is I have not detected it yet)

Thanks for the additional info Hiwall55.  That is good news.  I'd like to work in the subsonic ranges for some shooting.   I'm assuming the fit, without reduced bands, will result in a deeper seating depth and reduced powder column.   Plus there be a little cushion in bullet length that would help stability at lower velocity.       

QM, thanks for the suggestion.  I think I have five of the Accurate Moulds now.  All of them aluminum.   Last two I got (same order) had some issues.   Tom and I had a  different take on the cause and remedy but he cuts good holes for sure.   
      
I'm starting to favor steel moulds.  Not sure he'll cut another one for me but if he does it will be steel.   

With both his and my LBT I ordered sprue places with a trough joining the sprue holes.    That was when I bottom poured.   Now I've found I'm too much a dunce to master ladle pouring with double cavities that have that kind of a sprue plate.    Wish I could.   I know a gentleman over on CB who puts two nipples on his ladles.    Yesterday I resorted to the bottom spout again after fiddling and fumbling with different technique.    I'd make much prettier bullets and a lot faster if I could quit leaking in the direction of the trough before I am ready.  I thought I was pretty smart back when I ordered; now I'd trade for standard sprue.      

Sarge, that's a good observation, and when using a lube/sizer certainly something to avoid. I don't know how the "other" guys do it, but there must be a way. And, of course, there is the 'shoot 'em as cast' school. Most of the references I've seen are, apparently, gas checked, but I don't see that being the crux of the matter, and just figured I'd ask if any here had tried it with flat bases, maybe even breechseated. If it's foreign territory, I'll understand. I'm a curious sort. Not so curious that I'll lead a barrel just to find out- hoping somebody has tried this around here.