I know there's probably lots of information out there on the sensitivity of different powders and there is on many of the Hodgdon Extreme line of powders but I was really interested in IMR 8208 XBR as it really shot well for me in my .22-250 with great velocities but I couldn't find any good data on it, just many saying that it's pretty temperature insensitive. Well to relieve my curiosity a bit I did a little experiment to see how different rifle powders compared in the .308 Winchester cartridge and thought I'd post my findings for anyone interested.
Criticize if you want, I would have liked to have done a larger round count of each powder and with a wider temperature difference but due to limited supplies and available time I just shot 2 "Hot" rounds and 2 "Cold" rounds of each powder for comparison. With the exception of the IMR 8208 all rounds were loaded in Win brass with 155gr Barnes Match Burner, WLRM primers and at 2.800" OAL and I decided on the powder charge weight of each powder by going half way between starting and max loads listed on Hodgdon's website for a 155gr projectile, not necessarily the same one I was firing. As for the Alliant Reloader 15 I found the info on some forum for the min and max load and I knew 42.7gr was safe, for my rifle, as I had been loading a heavier dose behind a 175gr SMK. The RL-15 probably could have used a heavier dose of powder which may have affected it's difference between the hot and cold firing. I already had some loads made up with IMR 8208 and didn't have any powder left for this experiment but really the main comparison is being made between the round fired hot vs. cold. My IMR 8208 rounds were loaded in Lake City LR brass at 2.800" with 155gr Hornady Amax and WLRM primers @ a 43.6gr charge weight. I used magnum primers only because that's what I had. I'm not sure what affects a non-magnum primer would exhibit but this was my test and here are my results. The IMR 4895 had an opposite affect of what I would have thought. I got a sticky bolt and pretty good pressure signs with the cold rounds but not the hot. The temp was 86°F outside with varying sun which I tried to keep the "Hot" rounds in the sun. The cold rounds were inside a small dorm fridge freezer area until fired, I didn't take the temp reading in the freezer but there was ice build up inside and my frozen dinners were still solidly frozen so below 32°F for sure. I fired a few non test rounds before beginning the test just to not start out testing on a cold chamber and bore. I then started with firing one "Hot" round then running to the freezer, only 30' away, grabbing the two "Cold" rounds firing them as quickly as possible then firing the other "Hot" round, all of the same powder. I then proceeded through the same steps with the following powders until complete. All rounds were single loaded into the chamber of a 20" Remington 700 XCR Tactical Compact, factory barrel and chamber. *Note, none of these stated loads are recommendations for you to replicate, please consult a reputable reloading manual for safe loading data.*
Varget @ 45.5gr Hot Vel. 2685,2711 Cold Vel. 2710,2715 Avg. Difference (15fps)
Win 748 @ 46.5gr Hot Vel. 2817,2796 Cold Vel. 2699,2711 Avg. Difference (102fps)
IMR 4895 @ 45.5gr Hot Vel. 2769,2757 Cold Vel. 2798,2793 Avg. Difference (33fps)
H4895 @ 44.5gr Hot Vel. 2794,2803 Cold Vel. 2801,2805 Avg. Difference (4fps)
IMR 3031 @ 41.7gr Hot Vel. 2722,2715 Cold Vel. 2636,2639 Avg. Difference (81fps)
Reloader15 @ 42.7gr Hot Vel. 2534,2512 Cold Vel. 2426,2389 Avg. Difference (115fps)
IMR 8208 @ 43.6gr Hot Vel. 2804,2782 Cold Vel. 2753,2773 Avg. Difference (30fps)
Criticize if you want, I would have liked to have done a larger round count of each powder and with a wider temperature difference but due to limited supplies and available time I just shot 2 "Hot" rounds and 2 "Cold" rounds of each powder for comparison. With the exception of the IMR 8208 all rounds were loaded in Win brass with 155gr Barnes Match Burner, WLRM primers and at 2.800" OAL and I decided on the powder charge weight of each powder by going half way between starting and max loads listed on Hodgdon's website for a 155gr projectile, not necessarily the same one I was firing. As for the Alliant Reloader 15 I found the info on some forum for the min and max load and I knew 42.7gr was safe, for my rifle, as I had been loading a heavier dose behind a 175gr SMK. The RL-15 probably could have used a heavier dose of powder which may have affected it's difference between the hot and cold firing. I already had some loads made up with IMR 8208 and didn't have any powder left for this experiment but really the main comparison is being made between the round fired hot vs. cold. My IMR 8208 rounds were loaded in Lake City LR brass at 2.800" with 155gr Hornady Amax and WLRM primers @ a 43.6gr charge weight. I used magnum primers only because that's what I had. I'm not sure what affects a non-magnum primer would exhibit but this was my test and here are my results. The IMR 4895 had an opposite affect of what I would have thought. I got a sticky bolt and pretty good pressure signs with the cold rounds but not the hot. The temp was 86°F outside with varying sun which I tried to keep the "Hot" rounds in the sun. The cold rounds were inside a small dorm fridge freezer area until fired, I didn't take the temp reading in the freezer but there was ice build up inside and my frozen dinners were still solidly frozen so below 32°F for sure. I fired a few non test rounds before beginning the test just to not start out testing on a cold chamber and bore. I then started with firing one "Hot" round then running to the freezer, only 30' away, grabbing the two "Cold" rounds firing them as quickly as possible then firing the other "Hot" round, all of the same powder. I then proceeded through the same steps with the following powders until complete. All rounds were single loaded into the chamber of a 20" Remington 700 XCR Tactical Compact, factory barrel and chamber. *Note, none of these stated loads are recommendations for you to replicate, please consult a reputable reloading manual for safe loading data.*
Varget @ 45.5gr Hot Vel. 2685,2711 Cold Vel. 2710,2715 Avg. Difference (15fps)
Win 748 @ 46.5gr Hot Vel. 2817,2796 Cold Vel. 2699,2711 Avg. Difference (102fps)
IMR 4895 @ 45.5gr Hot Vel. 2769,2757 Cold Vel. 2798,2793 Avg. Difference (33fps)
H4895 @ 44.5gr Hot Vel. 2794,2803 Cold Vel. 2801,2805 Avg. Difference (4fps)
IMR 3031 @ 41.7gr Hot Vel. 2722,2715 Cold Vel. 2636,2639 Avg. Difference (81fps)
Reloader15 @ 42.7gr Hot Vel. 2534,2512 Cold Vel. 2426,2389 Avg. Difference (115fps)
IMR 8208 @ 43.6gr Hot Vel. 2804,2782 Cold Vel. 2753,2773 Avg. Difference (30fps)
