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I've got a fair supply of 8208 XBR so I decided to try out this powder for the 90gr TNT's, and save the faster powders for my heavier bullets. I used a Chargemaster to throw the powder, Hornady brass (1x fired), and CCI #450. My COAL was 2,200", which basically seats the base of bullet 2/3rd way into length of neck. Right around 31gr of powder the case is what I would normally call approaching 100% fill (powder at base of shoulder/neck junction), but there is room to drop a little more with the 1/3 empty neck space behind the bullet. I loaded a wider range for powder charges than what I needed, but I wanted to have the data points & group potential for comparison when shooting at different temps/velocities. Ideally, 8208 XBR is temp stable....always good to independently confirm how it looks at 35F-40F (worst coldest days of winter)... still a 60F swing.
Howa Mini 20" Heavy Barrel in B&C Stock. 3-shot groups at 100 yards in 95F heat. I removed the TB9 suppressor between groups and used a Chamber Chiller to cool down barrel to barely warmer than the "Feels Like 110F" (usually 10-15 minutes). The barrel on this rifle is what I would call a heavy sporter and heats up much quicker than my other rifles. I came to realize that if I don't remove the suppressor while using the Chamber Chiller it becomes a heat sump as all of heat in barrel is blown into/through the suppressor... barrel is cool and suppressor is still super hot. Barrel cools off much faster with it off and suppressor cools off in same time just siting on the bench.
29.3 gr chrono 2640 n / a 2637 2639 *used as foulers (clean barrel shots)
29.6 gr chrono 2660 2642 2657 2653 *used as foulers (clean barrel shots)
29.9 gr chrono 2726 n / a 2753 2740
30.2 gr chrono 2730 2734 2731 2732 *Best Group
30.5 gr chrono 2744 2813 2760 2772
30.8 gr chrono 2807 2805 2826 2813
31.1 gr chrono 2843 2822 2823 2829 * faintest indication of Ejector Swipe, no pressure signs on primers.
31.4 gr chrono 2837 2857 2851 2848 * faintest indication of Ejector Swipe & stiffer Bolt Lift (not massive and nowhere near Bolt Click), no pressure signs on primers.
n/a - human error. I forgot to re-arm Labradar between shots.
Howa Mini 20" Heavy Barrel in B&C Stock. 3-shot groups at 100 yards in 95F heat. I removed the TB9 suppressor between groups and used a Chamber Chiller to cool down barrel to barely warmer than the "Feels Like 110F" (usually 10-15 minutes). The barrel on this rifle is what I would call a heavy sporter and heats up much quicker than my other rifles. I came to realize that if I don't remove the suppressor while using the Chamber Chiller it becomes a heat sump as all of heat in barrel is blown into/through the suppressor... barrel is cool and suppressor is still super hot. Barrel cools off much faster with it off and suppressor cools off in same time just siting on the bench.
29.3 gr chrono 2640 n / a 2637 2639 *used as foulers (clean barrel shots)
29.6 gr chrono 2660 2642 2657 2653 *used as foulers (clean barrel shots)
29.9 gr chrono 2726 n / a 2753 2740
30.2 gr chrono 2730 2734 2731 2732 *Best Group
30.5 gr chrono 2744 2813 2760 2772
30.8 gr chrono 2807 2805 2826 2813
31.1 gr chrono 2843 2822 2823 2829 * faintest indication of Ejector Swipe, no pressure signs on primers.
31.4 gr chrono 2837 2857 2851 2848 * faintest indication of Ejector Swipe & stiffer Bolt Lift (not massive and nowhere near Bolt Click), no pressure signs on primers.
n/a - human error. I forgot to re-arm Labradar between shots.
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