Documented results from replacing the 12 FV factory stock with an Oryx Chassis

[CFJunkie]

Here are the results of another session with the 12 FV .223 mounted in 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 Monday morning, July 14 at 100 yards. Temperatures on Monday were from 74 to 79 degrees with winds from 2 to 4 mph. 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 (12^th 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 I planned the seating depths for three of the four the 77 grain bullets to achieve the a jump to the rifling – 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.

For one load with the TMK bullets, load 3 of the 4 shown, as an experiment, I set the jump back to 0.067 for the TMK bullets to see what effect it had on group size. The other two TMK loads have jumps from 0.023 to 0.018. That load has the largest load average of 0.289.

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 21.1 gr 2.296 1.752 wf 1.360 * 71/74 deg. F. Oryx 60 in.-lbs.	Sierra SMK #9377	77	2544	0.240	0.238	0.007	0.233	0.238	0.238	0.250
4	IMR4166 21.0 gr 2.340 1.750 wf 1.359 * 74/75 deg. F. Oryx 60 in-lbs.	Sierra TMK #7177	77	2541	0.240	0.253	0.067	0.147	0.242	0.264	0.306
4	IMR4166 21.1 gr 2.293 1.748 wf 1.360 * 77/77 deg. F. Oryx 60 in.-lbs.	Sierra TMK #7177	77	2543	0.289	0.290	.0042	0.242	0.264	0.316	0.332
3	IMR4166 21.0 gr 2.335 1.745 wf 1.360 * 79/79 deg, F. Oryx 60 in.-lbs.	Sierra TMK #7177	77	2541	0.261	0.295	0.067	.0183	0.295	.0304
15					0.257	0.250	0.050

Previous results with Sierra 77 gr SMK #9377 bullets with IMR4166 powder and Rem 7 ½ primers averaged 0.256 for 7 groups. Today’s results with the same bullet, powder and primer averaged 0.240 for 4 groups.
Previous results with Sierra 77 gr TMK #7177 bullets with IMR4166 powder and Remington 7 ½ primers averaged 0.273 for 8 groups. Today’s results with the same bullet, powder, primer averaged 0.263 for 11 groups.

Here are comparisons of the performance with Savage factory plastic stock versus the Oryx chassis

Comparison of 12 FV .223 Factory Stock with Oryx Chassis
--------------------------------------Savage Factory Plastic ----------------- Oryx Chassis
-------Bullets ---------------------- Avg. - Median St Dev # Grps. - Avg.-- Median - St Dev # Grps. -- Delta % Improv.
Sierra Match King # 1380 ------- 0.329 - 0.303 - 0.087 -- 10 ---0.307 - 0.295 -- 0.098 ----- 7 ----- 0.022 -- 6.7%
Sierra Tipped Match King #7169 0.304 - 0.288 - 0.061 -- 12 --- 0.258 - 0.272 -- 0.038 ----- 7 ----- 0.046 -- 15.2%
Sierra Match King # 9377 ------- 0.344 - 0.327 - 0.118 -- 11 --- 0.250 - 0.245 -- 0.016 ---- 11 ---- 0.094 -- 27.3%
Sierra Tipped Match King #7177 0.280 - 0.274 - 0.043 -- 12 --- 0.267 - 0.267 -- 0.051 ---- 19 ----- 0.012 -- 4.4%
------------------------------------ 0.313 - 0.289 - 0.082 -- 45 --- 0.269 - 0.267 -- 0.055 ---- 33 ----- 0.044 -- 13.9% w Oryx

Comparison of 12 FV .223 with CCI BR-4 versus Remington 7 1/2 Primers - equivalent Jump
----------------------------------------CCI BR-4 primers -----------------Remington 7 1/2 Primers
------------Bullets ------------------- Avg. Median St Dev # Grps. -----Avg. Median St Dev # Grps. Delta % Improv.
Sierra Match King # 1380--------- 0.399 0.422 - 0.078 -- 3 -------0.303 - 0.287 0.084 --- 14 -- 0.096 -- 24.2%
Sierra Tipped Match King #7169 0.354 0.339 -- 0.065 --- 5 -------0.264 - 0.272 0.030 -- 14 --- 0.090 -- 25.5%
Sierra Match King # 9377 --------0.352 0.287 -- 0.140 --- 8 -------0.265 - 0.250 0.038 -- 15 -- 0.087 -- 24.7%
Sierra Tipped Match King #7177 0.278 0.290 -- 0.044 --- 8 -------0.270 -- 0.267 0.050 -- 23 -- 0.007 --- 2.7%
-------------------------------------0.333 0.308 -- 0.098 -- 24 ------0.274 -- 0.270 0.055 --- 66 -- 0.059 -- 17.7% w Rem 7.5