I'm working with a new rifle project and new experimental cartridge  (26 cal using 25-35 parent cases) for offhand shooting.   I also have a new custom 2-cavity mould for the long heavy 26 cal bullet i ordered off a "group-buy" a few years ago.  I have been working on this rifle for a number of years and finding and squirreling away parts.  and its finally coming together.

  However I have run into a very small (literally) problem. When fire-forming the cases I find that the neck is just a very slight bit bigger than the bullet base. Its just a smidge bigger than a slip fit.   I have not dug out (relocated) some of my expanding ball gauges to measure the exact inner case neck diameter accurately yet but its really slight.

   I could order a die to size the brass down slightly but I'really don't want to always be resizing case-necks and working them too much.

   I might be able to send the mold somewhere and have the base band slightly enlarged----and/or have a stop ring added to the design.
   
  I have heard of "bump" dies that if I understand it---might be able to fatten up the base band a bit.   
I even read here about dropping them through a tube to "bump" the base out-----but that seems like a lot of uncontrollable variable to add---It might work on a big-bore BP bullet but doesn't sound real reliable for a smaller bore with Smokeless powder.

The other thing I think I have I have heard or read is that adding more tin to the alloy makes a slightly larger and slightly harder bullet. I have been shooting "woody-alloy"   25/1 as i recall. and I have a bunch of 50/50 solder in wire and bars I inherited from my plumber dad's work truck when he died that I could use to temper the all with.

Can some one confirm or deny my recollection as being accurate?  It would certainly be a quicker fix.

Myself, I'd add a little wheelweight or similar for the antimony. Never bothered me in small amounts. Most rifles, anyhow.
On the other hand, if you'd like to avoid that like so many seem to do, I don't think the small amount of necking you seem to need is a worry. I think that cases will last a long, long time if you only squeeze 'em a thou or two.

For what it's worth I often use an alloy I make up that's around half wheelweight and half soft lead. I do add a goodly amount of tin from solder bars to aid mold fillout. I never tested it, but I doubt the air cooled alloy is more than about 10bhn. It does cast about a thou or a little more larger than the mold in 20:1 lead/tin. I'm fortunate in having a rifle that seems to like the stuff either way.
I also shoot five cases fixed every time I head out for foulers. The five cases have been sized about two thou to grip the bullet. I just checked and they are on the 38th cycle now. No trouble with the small amount of sizing. This after having been reformed from .32 spl. into .32-40. 
It's worth a try since you'd only need to mix a small amount to test- or get it from a pal. Hope ya get 'er shootin' soon.

If a special order die is considered just buy an oversize neck bushing die and the correct bushing for your neck.  A 30-30 neck bushing die should do to hold the bushing. Your bushing will be about .02 larger than your bullet or about .284.