I, too, am in the process of pushing the 7mm envelope as far as it can go. I tried the Retumbo, and, like you, ran into pressure ceilings VERY quickly. I found that I could not achieve the case capacities that I needed with my case that I needed to get good performance. I was getting around 70% fill when I started seeing problems. Since I run a .338 Lapua necked to 7mm in relatively tight twist bbl, I find that the slower burning powders seem to work pretty well. With your RUM, the 872 should work pretty well with the heavier pills if you have the bbl to make use of it. I have a 7RUM and it loves the 872 with the 168 SMK's. I found that I had Cu fouling VERY quickly with this rifle, which a Rem M700 as well. I usually seat the bullet right on the lands, and drop back on the powder charge to compensate, but I still have seen bad fouling from the throat to about 8 or 10 inches down the bbl. Here again, the pressure curve on the 872 burn rate seems to help this since the burn of the powder charge is more evenly dispersed down a greater portion of the bbl instead of just blasting it through the throat so quickly. As you say, there ARE a few problems with temp sensitivity with the 872, but it seems to do the trick. One other powder I have had great results with (but also had hangfires and temp sens problems) is H870. Though it is no longer mfr'd, you can still find it right now on clearance at most reloading supply shops. I would grab a few lbs. of it and give it a try while surplus is still abundant. This might help give you some insight into what is going on. Now, I too must step down off my soap box! Peace bro!
TH
