Springfield 1903

[oldfoneguy]

I believe my barrel is a 4 groove

Ok, that will give a more conventional reading on the erosion gauge than a 2 groove barrel does. I've found that different types of rifling hold the gauge differently. For example 2 groove to 4/5 groove, button rifling to flat, Savage commercial to Savage Enfields and the list goes on. It's a matter of feel to know exactly when the gauge is seated properly in some or direct and unquestionable in others.