168 TMK false BC claims

uncledillers

uncledillers

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I had some of the new 168 tmk. Original plans was to do a load for a 18.5 Modern hunter, but lets just say that platform was conducive my desired end state. So I decided to do a load for a new to me custom savage 10 in 308. 24" bull barrel 1-10 twist. I ran some numbers through quikload and compared that to optimum barrel time charts and came up with a load. 42.65 gr of imr 4895 in FL sized hornandy match brass, cci br2 primers, and the 168 tmk set to a COAL of 2.800. Predicted MV of 2659 fps.

We had already had some similar rounds made up fot the MH and had run threw this rifle a week before so we new it wasn't any where near to hot.

went straight out to 1000m never have shot this load, just ran the numbers through JBM with projected mz and bc. We were Shooting threw a chrony to get actual mz. Winds were gusting from 5-8mph full value. Second round hit, and the another. MV was only of by 8fps, at 2651.Then we switched out rifles. After that we went on to 1150 meters.

At 1150 meters the wind was already picked up, gusting from 8-15 mph. Took a couple shots go get on but once one we managed to hit pretty consecutively.

The results overall were 13.2 Mil of elevation at 1000, and 17 MIL at 1150.
So when we compared the elevations and mv the actual bc was more like .450 BC. which is way under advertised BC, but very close to run of the mill 168 smk.

That being said they seemed to transverse into sub sonic alot better.
 
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I thought so but at the end of the artical it shows that "The 155gr TMK BC is identical to that of the 155gr SMK ", so its possible that the bc of the 168 tmk would be similar to the SMK.

And Iam just going of of elevation corection, muzzle velocity, and distance. I will look forward to seeing what Mr.Litz comes up with. And I was at a fairly low elevation around 1000ft
 
Before you start blaming Sierra's published BCs (which FWIW I don't have much faith in) there are other factors you need to check out and verify. Nailing down what a BC is is one of the harder problems in ballistics measurement, since you don't measure the quantity directly, rather, you deduce what it must be by observing small differences in other quantities that are affect by BC - trajectory and/or speed and/or time of flight. The BC that you "calculate" is *EXTREMELY* sensitive to surprisingly small errors in the measurements that you make.

- how do you know what the distance to the target was, and to what accuracy do you know that distance?
- what was the air density that day? (or equivalently, what was the altitude above sea level, air temperature, barometric pressure, and humidity)
- how much did your scope move from when it read "0 mils" to when it read "13.2" mils? Are you assuming that it moved 13.2 mils because it is a $2000 (or more!) scope? Or have you measured the actual amount of reticle/image movement that your scope produces?
 
I am not claiming to have a Brian litz type of BC result. I am just putting my findings. That shooting 168 tmk at 2650 fps, at 1000 ft, with a bp of 28.85, 80 % humidity, Temp of 8 degrees using gps and map verified distance gives a approx G1 bc of .450.
 
uncledillers said:
I had some of the new 168 tmk. Original plans was to do a load for a 18.5 Modern hunter, but lets just say that platform was conducive my desired end state. So I decided to do a load for a new to me custom savage 10 in 308. 24" bull barrel 1-10 twist. I ran some numbers through quikload and compared that to optimum barrel time charts and came up with a load. 42.65 gr of imr 4895 in FL sized hornandy match brass, cci br2 primers, and the 168 tmk set to a COAL of 2.800. Predicted MV of 2659 fps.

We had already had some similar rounds made up fot the MH and had run threw this rifle a week before so we new it wasn't any where near to hot.

went straight out to 1000m never have shot this load, just ran the numbers through JBM with projected mz and bc. We were Shooting threw a chrony to get actual mz. Winds were gusting from 5-8mph full value. Second round hit, and the another. MV was only of by 8fps, at 2651.Then we switched out rifles. After that we went on to 1150 meters.

At 1150 meters the wind was already picked up, gusting from 8-15 mph. Took a couple shots go get on but once one we managed to hit pretty consecutively.

The results overall were 13.2 Mil of elevation at 1000, and 17 MIL at 1150.
So when we compared the elevations and mv the actual bc was more like .450 BC. which is way under advertised BC, but very close to run of the mill 168 smk.

That being said they seemed to transverse into sub sonic alot better.
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If it has a polymer tip, the BC is incorrect out past 400m no matter which company it is... https://www.youtube.com/watch?v=VY3CKco6rqc
 
I don't think the bc of the bullets are wrong. Just that they would be better if they had non melting tips. Litz has used doppler befor to confirm actual bc of many bullets and many are on point or even better then advertised, even with melting tips. I have shot 178 amax before and they bc matched up pretty close to the advertised bc. These tmk did not.
 
uncledillers said:
I don't think the bc of the bullets are wrong. Just that they would be better if they had non melting tips. Litz has used doppler befor to confirm actual bc of many bullets and many are on point or even better then advertised, even with melting tips. I have shot 178 amax before and they bc matched up pretty close to the advertised bc. These tmk did not.
Click to expand...

I don't think Ive ever seen an advertized BC below actual...

I don't trust whats on the box, and my wind calls far outweigh the minor difference in B.C between the major players in long range projectiles.

I shoot 208 AMAX and 175 Berger VLD's. I have seen the 175 SMK's work fairly well so I'll run whatever is cheapest the next time I buy a few hundred.
 
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