Shipping your grip frame to me for fitting your grips means just that, shipping your grip frame only. Some people are under the impression that removing the cylinder from a revolver makes it legal to ship by USPS. This is not true. Rugers serial numbers are on the cylinder frame and this part is considered to be a gun by the ATF and must be shipped through an FFL.
The picture on the left below shows a grip frame ready to be shipped. The picture on the right shows what is illegal to ship.