One thing that should be pointed out as well, is that you need to know what your bore diameter is. Many antique Parker 10 guns (along with some others) have bore diameters of anywhere between .790-.810. This important to know, especially if you plan to load card wads. The Track hulls have an internal diameter to accept 9 gauge card wads, which is correct for 10 ga. guns that have a bore larger than the modern .775 standard.
As pointed out the RMC hulls are designed to accept modern components (i.e. smaller diameter wads). One is neither right or wrong, it just depends on what you plan to load in your particular gun. Shooting plastic wads in a oversize bore will work ok. However, if you want to load 9 gauge card wads (.815 diameter) in a RMC hull (.775 diameter), it would be very difficult. Decide on what kind of loads you want to shoot in your particular gun, then pick your hulls to match.
