I tried another experiment with the Savage 12 FV .223 with the Oryx chassis using the 36X single power Sightron 1-inch tube scope with a target dot reticle. The action screws were torqued to 60 in.-lbs. prior to this session to match the Oryx chassis torque specs.

I shot in two sessions on Thursday, Aug 16nd and Saturday August 22nd in Northern Virginia at 100 yards testing 69 gr TMK #7169 and 69 SMK #1380 bullets with IMR4166 powder and Remington 7 ½ BR primers. Somewhat uniquely, the 69 grain bullets with IMR4116 powder allow a range of loads that include both the 10th and 12th reflection exit times without exceeding Pmax. The 60 and 69 grain bullets are about the only bullet weights that can manage that. The test was to try one load of each at the 10th reflection exit time (1.134 msec. around 2584 to 2590 fps) and one load of each at the 12th reflection exit time (1.361 msec. at 2954 to 2589 fps) and them compare the results. Those exit times should be the sweet spots for a 26-inch 3% carbon steel barrel with a 0.040-inch recessed crown. (Estimated pressure and exit times were obtained from QuickLOAD.)

Temperatures on Friday and Saturday morning were both 75 to 85 degrees with standard high humidity from 8 to 10:30 AM with winds from 3 to 5 mph. Altitude of the range is 250 feet above sea level.
Although the bullets were of two types, the loads at each end of the range were quite similar with only slight variations in seating depth and trim length to accommodate the bullet themselves and their specific seating depths to achieve a 0.020 jump.
Even though the muzzle velocity of the 10th reflection averaged 374 fps higher than the 12th reflection and the pressure averaged 19,588 psi higher, there were no difference in pressure signs on the primers and no difference in the feel of the bolt on extraction.

The load description field shows the powder and charge, the O.A.L., the trim length, and the bullet exit time from the 26-inch barrel.

# Grps Load Description Bullet Weight Velocity Average Median St Dev 1 2 3 4
4 IMR4166 21.3 gr 2.348 1.747 wf 1.361 * 75/76 deg. F. Rem 7 ½ Oryx 60 in.-lbs. 37361 psi Sierra TMK #7169 69 2581 0..266 0..266 0.038 0.219 0.264 0.267 0.313
4 IMR4166 24.4 gr 2.344 1.744 wf 1.134 * 79/78 deg. F. Rem 7 ½ Oryx 60 in-lbs. 57246 psi Sierra TMK #7169 69 2954 0.323 0.333 0.093 0.211 0.285 0.381 0.416
4 IMR4166 21.7 gr 2.336 1.742 wf 1.361 * 83/82 deg. F. Rem 7 ½ Oryx 60 in.-lbs. 37456 psi Sierra SMK #1380 69 2594 0.276 0.290 0.041 0.215 0.288 0.292 0.308
4 IMR4166 21.0 gr 2.304 1.739 wf 1.134 * 83/77 deg, F. Rem 7 ½ Oryx 60 in.-lbs. 56747 psi Sierra SMK #1380 69 2569 0.277 0.281 0.035 0.233 0.266 0.295 0.313
16 0.285 0.287 0.056




The second load of TMKs were really impacted by the last groups of .416. Up until that group, the first three groups were averaging a somewhat respectable 0.292. The POI for the 10th reflection loads was 4 ½ inches higher than the 12th reflection loads. I expected some change in the POI but I was really surprised it was that much for a 375-fps change in muzzle velocity. That may have broken my concentration a bit, but I don’t think it caused the two larger groups testing that particular load although it was the first 10th reflection load tested.
That again shows how shooter induced variations can ruin good data. I have no explanation for that result, other than an error by the nut behind the trigger.
Comparing the results by 10th and 12th reflection time:
I gathered the data for each reflection time so I could compare the results by reflection time.
With the 0.416 group:
Refl. Exit Time Average Median St Dev
10th 1.134 0.300 0.290 0.070
12th 1.361 0.271 0.278 0.037
Delta 0.029 0.013 0.032

Excluding the 0.416 group:
Refl. Exit Time Average Median St Dev
10th 1.134 0.283 0.285 0.056
12th 1.361 0.271 0.278 0.037
Delta 0.013 0.008 0.018
The results, with and without the single 0.416 group that bothered me so much, really didn’t show a marked difference in results for the different reflections, given that the number of groups for each reflection was only 8 (with the 0.416 group) and 7 and 8 (without the 0.416 group). The differences between the combined data for the two reflections (even when including the 0.416 group) is within the normal variation in data for almost identical loads with the same velocity and pressure the I have been reporting.