Thought I would start this thread to get some good collective data on RL33 stability or temp sensitivity. Would like to get some results from others as well (collective data). How did you go about your testing and what chrony did you use, conditons, etc. The other day I went to the range to do some load development and while there shot some temp test rounds through the 300 RUM and 6-284. Abient temp was 20* and did some cold soaking to get the cold temp rounds down to that temp. I put the warm loads on the floor of my vehichle and maintained 75* after loading them inside at a temp of ~ 70*. Shot the cold rounds first letting the barrel cool between shots, then right after the last cold shot, I fired the warm rounds at a faster rate to keep the barrel warm. Chrony used was a MagnetoSpeed 300 RUM results, 230 hybrid Targets over 96 gr of RL33, 27" 5C Broughton. Note: Warm loads showed signs of excessive pressure Cold rounds, 20*..... 3101, 3082, 3095.. Avg, 3092 Warm rounds, 75* .. 3170, 3142, 3158.. Avg, 3157 Avg fps/degree diff = 1.18 fps/degree 6-284 results, 105 Hybrid targets over 60 gr RL33, 26" 5C Broughton (low pressure load) Note: First cold round was out of a freshly cleaned bore and showed signs of higher pressure, but not excessive. Could have been some left over cleaning residue in the bore. Cold rounds, 20*.... 3342, 3302, 3287.. Avg, 3310 (without first shot 3295) Warm rounds, 75*.. 3340, 3309, 3331.. Avg 3327 Avg fps/degree diff, 0.31 fps/degree Avg diff without 1st shot, 0.58 fps per degree I plan to do some more testing with the RUM when I get some new brass. I have some test rounds loded in the 6.5 WSM and will fire a few more through the 6-284 as well. If you have any data to add, please do.