Hornady sizing lube in the plastic tub works great, too.

Also, the neck relief may be somewhat difficult to gauge, as the crush fit that Daryl correctly recommends can mask compression in the neck area. If you can fire a round with an undersize bullet, you can then check to see if the proper bullets slide inside the fired case easily.

You CAN mike the OD of the neck of a loaded round but that measurement will only be useful if you actually know the diameter of the neck area of the chamber. Otherwise, all you will learn is if the OD is within normal spec of the .30-30 and it is possible the chamber neck isn't.

Of course, if you have a sloppy chamber, the .375 cases may be better for overall use than normal .30-30 cases are.

Thld 190 Savage bullets would be a great start. Other 180's would be too or Flat Pointing 220's. Brings up Daryl's suggestion for a cannelure tool again...