So far I only reload for the .223 and 17Rem Fireball. I've only used Benchmark and have had great success with it. I was on Saubier and was reading a sticky for Cooper rifles (posted in 2007 with data from Cooper). H335 is the recommended powder for the 17MkIV, which I would assume to be identical to the 17Rem Fireball. Is H335 a temperature sensitive powder? When I was doing my load development I was going up in 1/10gr increments to find the load my 17 liked. I'll go through that again with another powder, but would like to have one load that is good in the winter or summer and would stick with Benchmark for that reason if H335 isn't temperature stable like the Extreme powders are. As usual....thanks in advance.