Vall,
If you have a 311413, it would be a good start. They usually cast about .313 in 20/1.

Since your groove is small, your bore is going to have to be around .311 - .312 or you won't have any rifling, to speak of. Most 32/40 should have about .003 deep grooves but, I have one that has .002 deep grooves.

I can ream the a base band on that bullet ot .319 and it should shoot ok. It will look like this. I did the same thing to my German, .316 groove rifle.

Frank

If you  have worked with a 4 jaw chuck a lot it is not difficult to align a bullet mould. It might take a little patience. you might have to use a gauge pin to align the cavity with a gauge pin or make a pin to align the cavity.

the trick is to chuck only on the back 1/3 to 1/2 of the mold with short sections of tongue depressors between the mold and the check jaws.   
This will allow you to align the mold on axis. If there is any tilt of the mold block you just use a urethane hammer to straighten it in line with the spindle axis.

I on occasion rebore base band diameters for local shooting friends. NOTE I said Base Bands. Base Bands only! I am one of those who learned the hard way that going inside and trying to make any kind of significant change was not good. Not having a Lathe with digital display once you go inside you are quickly 
LOST! My procedure is as follows. In a 4 Jaw chuck using .03
thick stainless shim stock under ALL the jaws get the bore at the Base to run true to your best ability. Usually within .0005
or better, Some bores are not really round you know. Good ones will come in dead using a .0005 indicater. Once it looks good I go inside deeper with the indicater tip and see how the farther inside is running. If its OK then I can set up a Carbide Boring Bar of correct size for the Bore size I wish to create. If the person wants a specific size and supplies me bullet samples from the Mold from the Alloy he uses I can usually calculate the size to bore the Base Band to. I have Gage pin sets in .0005 increments and Intramike small bore measuring tools starting a .150 diameter and so can accurately bring the Base Band size to what ever is desired. I will only do this work on what I call Rattle Blocks, The Loose ones as made today. The original Ideal with Handles Integral do not have any kind of exterior Geometry to work from. HTH It is possible. Regards FITZ.

Thought I'd seen something before about lapping one out.  Found this from Texasmac.  Maybe just use the compound in the base band?

Regards, Joe


Re: opening up a bullet mould .003 ? 
Reply #1 - Feb 12th, 2009 at 1:06am 

Here ya go.
============
Lapping moulds to increase bullet diameter

- Cast up a couple of bullets in the mould.
- Remove the bullets and lightly coat the inside of the mould with fine valve grinding compound.
- Insert the bullet back in the mould and clamp the mould together.
- Use a drill press with a standard drill bit (#29 is a good choice).
- With the drill press running at the slowest RPM, slowly lower the bit into the center of the bullet.  The bit should grab the bullet and start to spin it.
- If you don’t have a drill press an alternative may be a hand drill, but I have not tried it.
- Keep the blocks firmly closed. Do a little at a time and clean the cavities.
- Cast some samples and measure them.  If the mould is not enlarge enough, use these bullets for additional lapping.
- Cast new bullets as you proceed and use in turn to continue lapping until you’ve reached the desired diameter.

Take your time and go slow or you'll remove too much metal.  Aluminum moulds cut fast. Iron ones are much slower.  Not only will the bullet diameter increase they will most likely drop out easier and the bullets will have a smoother surface.  You can also try to cast the screw in the bullet, but it’s really tough to get right (straight and centered).

Good luck.
Wayne   

I think the lapping might work if the entire mold needed to be enlarged, but not certain how it might work to just enlarge the base band.

Best tool to drive a lap in a mould is a Torx bit.   Drill the lap on center, (undersize), then force the Torx bit into the hole.  Over the years I've tried screws, even tried the drill bit trick (once, on the basis of internet advice).  Either didn't hold, or in one case the screw slowly drilled itself right out thru the lap's point and ruined the mould.

I too have used a reamer to enlarge a base band.  No problem at all, except I never seem to find another use for the $25 reamer.

If I wanted to just enlarge the base band on a mold and had access to a lathe with a 4 jaw chuck, that isn't much of a job to go in and take out a little bit. 
As to lapping out a mold cavity, if I wanted to enlarge or smooth  out the entire cavity I would use a bullet cast in that mold. Cast the bullet, cut the sprue and let every thing cool. To dirve the lap I have taken an old allen wrench and cut off the short leg giving you a straight hex shaft. Drill a hole the same diameter as the flats and then force the hex shaft into the hole. Use the sprue plate to center up your drill bit. Then put the hex shaft in the drill chuck and you can use that to force the shaft into the hole you drilled. Just remember to swing the sprue plate out of the way before inserting the shaft. 
Sam