I've been working up loads for a 7 RUM. I am getting ES numbers of 50-60 with both bullets I have tried. Powder is Retumbo and primers are CCI250's. I've never had this issue before. Any help is appreciated.
Tried US869 and it's worse. Up to 80 fps.
Last edited by buckbrush; 10-16-2011 at 11:33 AM..
How many different powder charges did you chrono?
Finding a powder charge with a low ES is the key, and is the biggest determining factor in establishing a good ES.
Also you may want to try US869,( it's a fine ball powder), if you can't get results with retumbo.
Sometimes you can get a powder bridging in the neck of high capacity small caliber cases with large extruded powder and that causes lots of problems, including High ES as well as pressure spikes.
RockZ is right on. Stick powders in such over bore cartridges are very prone to bridging int he case neck. Unfortunately Ball powders are the way to go here. While I don't have a 7RUM, I'm shooting a 7STW and have had similar issues with Retumbo, a 7 RUM has to be worse....LOL.
There are those out there who say that US869 isn't temp stable like Hodgdon has claimed. So far I haven't seen the diffrence. You should get better velocities with US869 Anyway. Vihtavori 20N29 is the only powder I know of that is slower and still a ball powder (I think). Load density seems to be optimum for these types of cases as well.