Most guns of today are standardized in terms of bore diameter and rifling characteristics. If you are dealing with a knowledgeable dealer, a simple request for “some hunting bullets for my 30-30″ will probably get you what you want. Unfortunately there are dealers who are not very knowledgeable and a few who are mainly interested in unloading what they have in stock. “Caveat emptor” is still the safest position to take.
This section refers to getting the “best” bullet. The first thing you should have in mind when you go to buy bullets is a clear idea of what “best” means for your intended use. For any gun the first consideration for any use should be accuracy. Whether it’s for target or game, an inaccurate bullet is worthless.
The quickest and easiest rule of thumb when it comes to buying bullets is to get what duplicates the factory loading. If you want ammunition for special purposes, which most handloaders eventually will, then you will have to do a little research like reading this book. Old guns and those of foreign extraction can often be confusing in regard to what their bore and groove size actually is. The best information collected over the past century indicates that the most accurate bullet is the one that fits the groove diameter of the barrel exactly. In the final analysis this is determined by slugging the bore of your gun and measuring the slug with a micrometer or vernier caliper and getting bullets that fit.
Proper diameter bullets can most easily be determined by reading the information on the box they come in or by measurement, if you are buying bullets in a plastic bag from someone you don’t know. This can be a little confusing. For instance, 22 caliber bullets for the early 22 Hornet rifles were properly .223″ diameter. The modern ones are .224″. And the 223 Remington (5.56mm) is .224″ diameter, not .223″!
Good loading manuals usually give warnings regarding groove diameters in the data they provide for foreign and early rifles if there is a considerable variation in these within a particular type of rifle. My Lyman manual indicates that groove diameters on the 303 British military rifles vary from .309″ to .317″! Put too fat a bullet in one of the tight ones along with plenty of powder and you can create a dangerous pressure situation in addition to inaccurate shooting. The 303 Enfield, if loaded properly, is a fine, accurate rifle, capable of turning in some excellent groups.