Both of the replies above are correct. You can solve the problem by expanding the case larger, sizing the bullets smaller, or a combination of both.
As far as expander dies, Lyman makes the "M" die, RCBS makes a case expander die, and Lee also makes an expander die.
I'm not sure I can remeber the differences between the three, but as I best recall: the Lee die comes complete with 2 different tapered expanders which are good for many diameters of cases. For the RCBS, you can buy extra expander plugs for various diameters, and for the Lyman, I think you have to buy a new die each time you want a different diameter.
However, if you have a small lathe, or maybe even a drill press, you can turn your own expander plugs from mild steel for the Lyman and RCBS die bodies.
One thing to remember - if you expand the case to accept the bullet, you wil lmost likely have to crimp, at least a little bit, to remove the slight flare that the expander die put on the cases. If you don't, the cases won't chamber.