Here are the latest results 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 meet the Oryx chassis torque specs.
The session took place in Northern Virginia on Friday morning, July 19 at 100 yards. Temperatures on Friday were typical for a Virginia summer ranging from 79 to 91 degrees from 8 AM to 11 AM with winds from 2 to 5 mph. The combination of high humidity and temperature put the ‘felt temperature ranges’ just at the ‘heat alert’ range at 100 degrees by 11 AM so I made sure I was finished before the temperatures got that high. Fortunately, our range has the firing line under a roof so it never got over 86 deg. F. in the shade. Altitude of the range is 250 feet above sea level.
All the loads were shot using Lapua brass with Remington 7 ½ small rifle primers. All bullets were loaded to achieve a 1.359 to 1.360 msec. exit time (12th reflection) to stay under Pmax using the 77 grain bullets with IMR4166 powder. The 1.359 to 1.360 exit time should be the sweet spot for a 26-inch 3% carbon steel barrel with a 0.040-inch recessed crown.
For this session, I loaded IMR4166 Enduron powder and 77 grain Tipped Match King #7177 bullets with the seating depths for the 77 grain bullets to achieve the a jump to the rifling – 0.030 to 0.020 – and then adjusted the seating depth by less than 0.005 thousandths to achieve the 1.359 to 1.360 exit time to accommodate variations in the brass trim length. As a result, all the loads are quite similar with only slight variations in seating depth and trim length.
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 21.0 gr 2.340 1.750 wf 1.359 * 83/82 deg. F. CCI BR-4 Oryx 60 in.-lbs. Sierra TMK #7177 77 2541 0.256 0.236 0.043 0.230 0.236 0.236 0.321 4 IMR4166 21.0 gr 2.337 1.748 wf 1.359 * 86/82 deg. F. CCI BR-4 Oryx 60 in-lbs. Sierra TMK #7177 77 2541 0.267 0.266 0.016 0.249 0.265 .0266 0.288 4 IMR4166 21.1 gr 2.353 1.745 wf 1.359 * 90/84 deg. F. Rem 7 ½ Oryx 60 in.-lbs. Sierra TMK #7177 77 2545 0.278 0.282 0.038 0.229 0.277 0.286 0.320 4 IMR4166 21.1 gr 2.351 1.743 wf 1.359 * 92/86 deg, F. Rem 7 ½ Oryx 60 in.-lbs. Sierra TMK #7177 77 2545 0.310 0.306 0.024 0.285 0.302 0.309 0.343 16 0.278 0.281 0.035
I was surprised that the CCI BR-4 primers out performed the Remington 7.5 primers by a slight margin today, especially since the Remington primers were shot in rounds that were seated out at the preferred O.A.L. to get the jump closest to the 0.020 jump at which the TMKs usually perform best.
It could have been the shooter losing concentration in the heat, but it didn’t seem to be affecting me all that much.
I allowed the rifle to cool down after the barrel temperature got around 130 deg. F. on the LCD temperature strip I have on the barrel. It was never calibrated, but it did ensure that the barrel temperature didn’t get too high with any load.
The overall 5-round group average has improved from 0.351 to 0.322 since mounting the Oryx chassis and shooting the 77 grain SMK and TMK bullets in the 1:9 twist barrel (averaging 0.271 primarily with 69 and 77 grain bullets). Prior to trying the bullets that are universally believed to be unstable in a 1:9 twist barrel, the overall group average for bullets from 50 to 70 grains was 0.362.
Bullet Weight Performance Ranked By Average
Weight Avg.- Median St Dev # Grps. Rank
-- 77 - 0.281 0.267 - 0.065 -- 70 ---- 1
-- 69 - 0.313 0.286 - 0.083 -- 39 ---- 2
-- 55 - 0.343 0.305 - 0.094 --- 4 ---- 3
-- 52 - 0.366 0.382 -0.079 -- 11 ---- 4
-- 53 - 0.376 0.366 - 0.082 --- 8 ---- 5
-- 50 - 0.390 0.392 - 0.064 --- 3 ---- 6
-- 60 - 0.487 0.487 - ------ --- 1 ---- 7
-- 70 - 0.619 0.670 - 0.189 --- 4 ---- 8
-- 68 - 0.653 0.653 - 0.001 --- 2 ---- 9
- All -- 0.322 0.288 - 0.106 - 142
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