Hornady 6.5 Grendel Brass, Hornady 123gr A-Max, CCI 450 and IMR 8208-XB, 24" barrel

[dgp1000]

Here's some better info. Any help interpreting would be much appreciated.

All results were using Hornady brass (first load), CCI 450, IMR 8208-XBR and Hornady A-Max 123gr bullets. COL was 2.260". 100 yards.

28.7g - 2694, 2706, 2675, 2721, 2711, 2673, 2736, 2688, 2696, 2721, 2673, 2679, 2668, 2679, 2692, 2721, 2692, 2712, 2692, 2676.
28.8g - 2728, 2717, 2723, 2714, 2729, 2663, 2735, 2729, 2740, 2709, 2710, 2719, 2687, 2724, 2685, 2717, 2697, 2698, 2717, 2682.
28.9g - 2764, 2748, 2779, 2737, 2761, 2728, 2730, 2738, 2741, 2729, 2748, 2757, 2763, 2786, 2788, 2754, 2707, 2698, 2719, 2728.
29.0g - 2710, 2715, 2745, 2726, 2730, 2722, 2734, 2727, 2745, 2702, 2740, 2708, 2744, 2735, 2715, 2754, 2712, 2756, 2748, 2748.

24" LW barrel 1/8" twist.

The groups were great but was only shooting 100 yards. No signs of over pressure on the fired brass.

Thanks!

[Drifter]

Here's some better info. Any help interpreting would be much appreciated.

All results were using Hornady brass (first load), CCI 450, IMR 8208-XBR and Hornady A-Max 123gr bullets. COL was 2.260". 100 yards.

28.7g - 2694, 2706, 2675, 2721, 2711, 2673, 2736, 2688, 2696, 2721, 2673, 2679, 2668, 2679, 2692, 2721, 2692, 2712, 2692, 2676.
28.8g - 2728, 2717, 2723, 2714, 2729, 2663, 2735, 2729, 2740, 2709, 2710, 2719, 2687, 2724, 2685, 2717, 2697, 2698, 2717, 2682.
28.9g - 2764, 2748, 2779, 2737, 2761, 2728, 2730, 2738, 2741, 2729, 2748, 2757, 2763, 2786, 2788, 2754, 2707, 2698, 2719, 2728.
29.0g - 2710, 2715, 2745, 2726, 2730, 2722, 2734, 2727, 2745, 2702, 2740, 2708, 2744, 2735, 2715, 2754, 2712, 2756, 2748, 2748.

24" LW barrel 1/8" twist.

The groups were great but was only shooting 100 yards. No signs of over pressure on the fired brass.

Thanks!

Regardless of how the brass looks, I think you might be past max. The velocity deviations between shots with the same charge seem excessive and erratic. And then the velocity appears to sometimes decrease despite an increase in charge weight.

Isn't the book max 28.5? And for what it's worth, the 28.5 charge with a 123gr bullet seems excessive in the barrels that I've tried it in.

Personally, I think 8208 is a tad fast for 123gr bullets, as loads seem to go from safe to excessively hot with a relatively small change in charge. I plan to test it more with lighter bullets, but I prefer a different propellent for 123gr.

Not trying to discourage those with good results, but perhaps a little extra caution is advisable. If the brass isn't talking to you, play close attention to how the weapon functions when fired.

[bobke]

I blew a whole primer smooth out of the pocket at 28.3 gr of 8208 and 120 Nosler BT, these loads seem well beyond that threshold, though every barrel is different. At least a tenth or so down is my new practical max.

[rasp65]

dgp1000 Here are the statistics on your data. As Drifter pointed out you lost velocity with the highest load.

123Hornady A-Max				
IMR-8208	28.7 gr	 28.8 gr 28.9 gr 29 gr
Ave	        2695.3	 2711.2	 2745.2	 2730.8
SD	         19.76	  20.02	  24.48	 16.55
Min	          2668	  2663	   2698	 2702
Max	          2736	  2740	   2788	 2756
ExtSpread	    68     77	    90	    54

[LRRPF52]

I was thinking the same thing about the extreme spreads. The chronograph is a better indicator of pressure than early signs on primers and brass. When erratic velocities start showing up, something strange is happening.

That said, do you have any pictures of the brass? What buffer and bolt carrier weight are you using? What was the temp outside?

[dgp1000]

Thanks for all the feedback guys and the stats rasp65. Very useful info. I see I lost Velocity at 29.0gr however the spread was the lowest of all, interesting.

LRRPF52, I have the brass and will take some pictures and upload for you asap. Perhaps I am missing something. It's always good to have a second set of eyes to check things out. Do you think you think the extreme spread correlates in any way with the barrel timing information you posted earlier in this thread?

"It lists the OBT's for a 24" at (all numbers in mS):

0.8160
0.8948
1.0221
1.1016
1.2282
1.3084
1.4343
"

Apologies for the late response, just back from a (too!) short vacation.

[LRRPF52]

If the case wall down near the base, just above the extractor groove, is not bulged or deformed, and you don't have cratered primers, I would just go with the most accurate load that is closest to 50,000psi, so you don't shear bolt lugs.

[dgp1000]

Here's a selection of spent cases from across all four loads. I see a very slight mark down near the extractor groove but no signs of bulging. What do you think?

[LRRPF52]

That brass all looks good to me, from what I can see. I don't see any signs of cratered primers, bulged bases in the web, so from the moderate detail in the pics, they look ok. I would want to see a perfect perpendicular angle from the side to see if there is any primer cratering, but it doesn't look like there is any.

[Drifter]

See how difficult it is to nudge the fired cases into a case gauge. If difficult, color with a Sharpie pen to help determine which part of the case is resisting.

[dgp1000]

Apologies for the poor quality pictures but what you say to look for and what I see makes me feel pretty confident these cases/primers are fine. I should have ordered a case gauge a while back and saved you all some grief, thanks!

At 100 yards all four loads seemed as accurate as each other. I think it's time to try the 300 yard range.

[GONE2VT]

Apologies for the poor quality pictures but what you say to look for and what I see makes me feel pretty confident these cases/primers are fine. I should have ordered a case gauge a while back and saved you all some grief, thanks!

At 100 yards all four loads seemed as accurate as each other. I think it's time to try the 300 yard range.

I know this thread has not had any activity in a while but thought I'd check in and see how it's going? Have you found a load that you're really happy with? Also, how did it shoot at 300 yards?