Black Hills 77gr OTM/TMK Comparision

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General Info

I decided to do a head to head comparison of a match 77gr SMK load compared to the new 77gr TMK. Rather than comparing a hand load tuned for a specific barrel, I chose to use Black Hills loadings as a factory "Match" loading. I figured I would share the results if I was going through the work anyways.

Notes on Data:

TMK – Black Hills 77gr TMK 556 Load – New Red Box
SMK – Black Hills 77gr OTM 556 Load – New Red Box



All velocities were recorded separately from group tests using a Magneto Speed attached at the muzzle.

100yrd groups were shot at an indoor range with ammo at room temp (~70F). All groups were shot during a 2 minute interval. Sequence: Fire 5, load 5 more, and fire second group of five. Approximately 10 seconds between rds. I was mainly looking for extreme spread during relatively rapid fire.

600yrd groups were shot outdoors on a 60-65F day with density altitude of 6700-7000ft. Winds were mild at 2-3mph. Shots were taken at a rate of 1rd per 5 minutes. I was attempting to maximize accuracy in a slow fire scenario. Environmental variables were captured using a Kestrel 4500.

Disclaimer: I am by no means an expert. This is a one batch, simple, amateur test with nothing calibrated. Results will vary.

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Tear Down
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100yrd 20” Barrel Data

Barrel Info: 20” Rainier Arms Ultra Match with Fluted DMR Profile, Rifle Gas, 1:8 Twist
Federal XM193 Velocity = 3310 FPS

SMK 10rd Chronograph Data
Average = 2795 FPS
Standard Deviation = 9.6 FPS
Max = 2812 FPS
Min = 2781 FPS



TMK 10rd Chronograph Data
Average = 2792 FPS
Standard Deviation = 15.7 FPS
Max = 2826 FPS
Min = 2771 FPS



Group Test - 10rds SMK
Extreme Spread = 1.47” [1.40 MOA]
Mean Radius = 0.53” [0.51 MOA]



Group Test - 10rds TMK
Extreme Spread = 1.65” [1.58 MOA]
Mean Radius = 0.59”[0.56 MOA]

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100yrd 16” Barrel Data

Barrel Info: 16.1” BCM Non-Hammer Forged Chrome Lined, Mid-length, Light Weight, 1:7 Twist
Federal XM193 Velocity = 3062 FPS

TMK 10rd Chronograph Data
Average = 2635 FPS
Standard Deviation = 23.5 FPS
Max = 2675 FPS
Min = 2635 FPS



Group Test - 10rds TMK
Extreme Spread = 1.29” [1.23 MOA]
Mean Radius = 0.50” [0.48 MOA]

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100yrd 12.5” Barrel Data

Barrel Info: 12.5” Rainier Arms Ultra Match, Carbine Gas, 1:8 Twist
Federal XM193 Velocity = 2960 FPS

TMK 10rd Chronograph Data
Average = 2540 FPS
Standard Deviation = 16.6 FPS
Max = 2575 FPS
Min = 2516 FPS


Group Test - 10rds TMK
Extreme Spread = 2.21” [2.11 MOA]
Mean Radius = 0.63” [0.60 MOA]
Note: Taped hole is XM193 sighter, this group had a major shift in zero and crossed over targets.

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600yrd 20” Barrel Data

BC Values used for drop calculation G1 BC / Min FPS

77gr SMK
0.372 / 3000
0.362 / 2500
0.362 / 1700
0.343 / 0

77gr TMK
0.420 / 2400
0.415 / 2000
0.395 / 1750
0.380 / 0

Group Test - 5rds SMK
Extreme Spread = 7.61” [1.21 MOA]
Mean Radius = 2.41” [0.38 MOA]
Correction from 100yrd zero = 15.0 MOA



Group Test - 5rds TMK
Extreme Spread = 4.93” [0.79 MOA]
Mean Radius = 2.10” [0.33 MOA]
Correction from 100yrd zero = 13.8 MOA



Calculated Advantage of TMK = 1.2 MOA Less Drop
Test Advantage of TMK = 0.9 MOA Less Drop

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Summary

The TMKs grouped well at range for a non-tuned factory load. They also seemed to be a little more forgiving in the wind shooting other targets outside the group test. Wind improvement was calculated as an 15% decrease in required hold at 600yds, I did not specifically test wind drift. Data below is calculated using the above BC values used for 600yrd tests and assumes DA of 6000FT.




The best improvement with the new TMK seems to be Expansion/Fragmentation. Using the above data and assuming the 1900fps limit published by Sierra lines up with the real world.

20” Frag Range - 535yds
16” Frag Range - 448yds
12.5” Frag Range - 393yds

This practical range is quite impressive especially in the SBR. I have seen a few people post results from hunting that make the 1900fps limit seem like a real world value.

I'll update the above as I finish up.

[Great-Kazoo]

Thanks for the info. All i see is <Group Photo> No pictures.

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Group photos should be up now. Still need to process photos of fired case heads. I'll try to update the above later this week.

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Added case head photos, sequence numbers to 100yrd groups, and summary table comparing SMK/TMK in 20 inch.