There have been several prior posts on 100 CX Testing (#573-582, 596) that have led to this conclusion.
Thank jawjaboy for pulling 100 CX bullets from factory Hornady ammo (Lot # 949179) and contributing them for testing. His lot of factory 6.8mm SPC ammo had the same crimp/finishing marks just below the ballistic tip as the component bullets. Macatac also confirmed his factory Hornady ammo (Lot # 3221532) had the crimped just below the ballistic tips. Testing with jawjaboy’s bullets, minimum velocity expansion was consistent with the component 100 CXs tested so far where velocities 2210 fps and below did not expand and yawed like an FMJ. Testing at a higher speed of 2290 fps, the 100 CX finally did open up with expansion deep into the expansion chamber. The expanding petals did break away but I will have to test further to determine if that is due to the CX being a softer copper than the GMX or the testing method used. Note, a 6.8mm CX on-line review from another shooter stated he was getting failure to open at mid-range velocities and loss of petals when speeds were high enough to effect expansion.
So, what is going on. After impact, a bullet must shorten and expand to a larger diameter to remain stable. Anything the delays expansion, as is happening here, will cause the bullet to be unstable in the denser medium, yaw, and fail to expand. The previous tests with the BTs removed showed proper expansion at speeds below 1600 fps so the expansion cavity is not causing any issues. The remaining factor(s) that could be delaying expansion would be the bullet’s copper gripping the BT to tightly and/or the increased hardness of these new tips. I found some .308 150gr CX bullets that do not have the crimp and will test them and then smaller calibers to further determine the details of why Hornady’s new CX bullet is not providing optimal expansion.
Meanwhile, what does a hunter do with a good bullet that turns into an FMJ after 150 yards (or closer to 100 yards with a shorter barrel). I suggest one of two options. You could resort to shoot hogs through the shoulder blade to create bone fragments that will improve terminal performance (not easy to do if they are running). Or, remove the obstruction that is preventing expansion, e.g., the bullet’s ballistic tip. This will give you a bullet with good expansion to 350 yards and beyond depending on your muzzle velocity. Good medicine for hogs and even better for coyotes. I tested two configurations: 1) with the BT removed but stem still in-place, and 2) BT removed with the stem pushed into the expansion cavity. As you can see in the test results below, leaving the stem in place did not impede expansion. Even with the lower BC (G1) of 0.230 vs 0.303, there is less than an inch difference in trajectory at 200 yards. I did a quick accuracy test with two 3-shot groups at 100 yards. POI did not change and accuracy was not degraded with the tips removed. Below is a link to a new thread on how to accomplish BT removal if you want to recover the performance potential of your 6.8mm SPC 100 gr CX bullet and ammunition.
(38) Hornady’s New CX Bullet: How to Restore Terminal Performance | 6.8 SPC Forums (68forums.com)
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Thank jawjaboy for pulling 100 CX bullets from factory Hornady ammo (Lot # 949179) and contributing them for testing. His lot of factory 6.8mm SPC ammo had the same crimp/finishing marks just below the ballistic tip as the component bullets. Macatac also confirmed his factory Hornady ammo (Lot # 3221532) had the crimped just below the ballistic tips. Testing with jawjaboy’s bullets, minimum velocity expansion was consistent with the component 100 CXs tested so far where velocities 2210 fps and below did not expand and yawed like an FMJ. Testing at a higher speed of 2290 fps, the 100 CX finally did open up with expansion deep into the expansion chamber. The expanding petals did break away but I will have to test further to determine if that is due to the CX being a softer copper than the GMX or the testing method used. Note, a 6.8mm CX on-line review from another shooter stated he was getting failure to open at mid-range velocities and loss of petals when speeds were high enough to effect expansion.
So, what is going on. After impact, a bullet must shorten and expand to a larger diameter to remain stable. Anything the delays expansion, as is happening here, will cause the bullet to be unstable in the denser medium, yaw, and fail to expand. The previous tests with the BTs removed showed proper expansion at speeds below 1600 fps so the expansion cavity is not causing any issues. The remaining factor(s) that could be delaying expansion would be the bullet’s copper gripping the BT to tightly and/or the increased hardness of these new tips. I found some .308 150gr CX bullets that do not have the crimp and will test them and then smaller calibers to further determine the details of why Hornady’s new CX bullet is not providing optimal expansion.
Meanwhile, what does a hunter do with a good bullet that turns into an FMJ after 150 yards (or closer to 100 yards with a shorter barrel). I suggest one of two options. You could resort to shoot hogs through the shoulder blade to create bone fragments that will improve terminal performance (not easy to do if they are running). Or, remove the obstruction that is preventing expansion, e.g., the bullet’s ballistic tip. This will give you a bullet with good expansion to 350 yards and beyond depending on your muzzle velocity. Good medicine for hogs and even better for coyotes. I tested two configurations: 1) with the BT removed but stem still in-place, and 2) BT removed with the stem pushed into the expansion cavity. As you can see in the test results below, leaving the stem in place did not impede expansion. Even with the lower BC (G1) of 0.230 vs 0.303, there is less than an inch difference in trajectory at 200 yards. I did a quick accuracy test with two 3-shot groups at 100 yards. POI did not change and accuracy was not degraded with the tips removed. Below is a link to a new thread on how to accomplish BT removal if you want to recover the performance potential of your 6.8mm SPC 100 gr CX bullet and ammunition.
(38) Hornady’s New CX Bullet: How to Restore Terminal Performance | 6.8 SPC Forums (68forums.com)
