CMV
Member
From today's range session I'm left with a question about signs of overpressure.
After inspecting my ejected cases, I noticed the one round I fired loaded at max had a widened & flattened primer. I'm a little confused about it though.
The load is 55gr Hornady FMJ, H335, CCI #41 primer, & LC brass. Fired from a 20" AR-15 with 5.56mm chamber.
The chrony results were off & everything was reading higher than last trip including factory rounds from the same lot. It's probably because the range is uneven on hilly ground so I'm shooting from a nice level platform but the backstop is a little lower so the rounds are passing through the chrony at a downward angle. I probably had the angle set a little off from the angle of the shot. That's all I can think of because my loads at the same charges and the XM193 were both reading right around 135 fps higher. Anyway, the average FPS for these batches were:
24.8 gr - 3054 fps
24.9 gr - 3102 fps
25.1 gr - 3212 fps
25.3 gr - 3299 fps
XM193 - 3405 fps
I'd say 100 - 135 fps lower is reality.
Anyway...... The round I fired at max load (25.3 gr per my data) has a primer that looks (to me) like its showing signs of overpressure. The XM193 is still much hotter. The couple I pulled & weighed had charges of 26.9 gr & I thought H335 & what's in LC ammo were very similar. Even so, XM193 should build a lot more pressure than a published max .223 load. So why would I get a flattened primer on my max load and no issues with XM193?
Or am I reading this wrong & that's a normal primer? (it looks different enough to me to at least ask). I don't really intend to make large batches at max load - I just thought I'd see how much difference there was. Should I try a few more or leave it alone & stay under 25.3 gr?
After inspecting my ejected cases, I noticed the one round I fired loaded at max had a widened & flattened primer. I'm a little confused about it though.
The load is 55gr Hornady FMJ, H335, CCI #41 primer, & LC brass. Fired from a 20" AR-15 with 5.56mm chamber.
The chrony results were off & everything was reading higher than last trip including factory rounds from the same lot. It's probably because the range is uneven on hilly ground so I'm shooting from a nice level platform but the backstop is a little lower so the rounds are passing through the chrony at a downward angle. I probably had the angle set a little off from the angle of the shot. That's all I can think of because my loads at the same charges and the XM193 were both reading right around 135 fps higher. Anyway, the average FPS for these batches were:
24.8 gr - 3054 fps
24.9 gr - 3102 fps
25.1 gr - 3212 fps
25.3 gr - 3299 fps
XM193 - 3405 fps
I'd say 100 - 135 fps lower is reality.
Anyway...... The round I fired at max load (25.3 gr per my data) has a primer that looks (to me) like its showing signs of overpressure. The XM193 is still much hotter. The couple I pulled & weighed had charges of 26.9 gr & I thought H335 & what's in LC ammo were very similar. Even so, XM193 should build a lot more pressure than a published max .223 load. So why would I get a flattened primer on my max load and no issues with XM193?
Or am I reading this wrong & that's a normal primer? (it looks different enough to me to at least ask). I don't really intend to make large batches at max load - I just thought I'd see how much difference there was. Should I try a few more or leave it alone & stay under 25.3 gr?