SoCal44 wrote:Can the Rio Grande 45-70 be safely loaded to the Marlin 1895 specs. (which I believe is < 40,000 CUP)? In my reloading manual I see Trapdoor loads, Marlin Levergun, and Ruger #1 loads. I'm assuming I can use the Marlin loads.
Here is my take on it. The RG4570 is a 336 clone not a 1895 Clone. The 1895 action has a little more beef where the receiver meets the barrel threads. That said, here is how I'm proceeding with my RG4570 based on my pressure trace testing experience.
When using that equipment, barrel outside diameter vs. chamber diameter and brass thickness are settings used to calibrate the strain gauge. Using the RG3030 as the "know"; with its pressure standard against and dimensions against those of the RG4570 I feel good in estimating, for my use, what the RG4570 is capable of.
I use CIP standards where I can as they relate directly to what I see with the strain gauge equipment. The 30-30 has a 46.4K PSI Pmax and 40.6K PSI NMP (Nominal Max Pressure). Loads are generated to NMP so that the variations can be contained within the PMax. Pressure, just like velocity, varies and nothing should exceed the max.
For my RG4570 I compared how much metal is around the chamber to how much metal was around the chamber of my RG3030 (now a 38-55), and I use 40.3K PSI as the Pmax and 35.3K PSI as NMP. The larger bore leaves less metal and there is no way the chamber can handle the same pressures that the 30-30 is being subjected to. What that is in CUP, I don't know. I can guess at it but use data with PSI results in my reloading. This 35K PSI target is not that far off of what I use in my Marlins. For the "G" I use a 48.0K PSI Pmax and 42.0K PSI NMP.
Using a 350-grain bullet as an example and with the above referenced pressures, I would expect to see about 100 FPS less in my RG4570 with the typical powders used in this cartridge. My Guide Gun would produce 2060 FPS and the RG4570 1960 FPS. That is still an amazing amount of killing authority.
All of us 45-70 shooters realize that we kind of operate outside the box at our own risk. Using Marlin 1895 data in the RG4570 is a bigger risk than I will take.