Oh yes I too have "learned" about Rl22, also the hard way, as in hadn't been handloading for even a year yet, worked up a smokin' hot and stupid accurate load in my .270 in November (in what is considered northern Saskatchewan - geographically about the middle )...only to find that my awesome load seized up the bolt come June - this constituted a nearly 50 degree celcius difference. Original 7828 and 7828 ssc didn't do that, but it does swing wider than the enduron powders when the temp difference is great, never in a "is this even safe?" way though.I haven't tried the endurons in my 257s but I suspect your hunch is right on Calvin. I have found in the 257 that 7828ssc to not be very temp sensitive. It's easy to test for yourself. Just put a few in the freezer and let them rip. My test confirm that at below freezing my tune stays good and I lose only 35 fps from a 70 degree load. Rl22 is a great powder in the 257 but it loses over 100 fps in the same test. Found out the hard way about the rl22. If you get a good node going with the h1000 you will be in good shape.
Shep
Temp sensitivity is different in each cartridge the powder is loaded in. Even bullet weight changed it some. The only way to know exactly what your drop in speed will be is to do the test in your own rifle. This is why there is no charts from the manufacturer telling us a percent per degree of speed drop. It's to variable. But I definitely do not load rl22 and rl26 anymore.
Shep