Sierra TMK

[liltank]

Hi Bryan,
Have you done any work yet with the Sierra 175 TMK? If you have, how soon will we see the info in the Ballistics and Shooter App? What numbers have you come up with? Very curious as I have found a good load that shoots the TMK well from my rifle. I like to use your data when setting up my DOPE on my apps.

Thanks,
Tank

 

[Park ranger]

I'm also looking forward to your work regarding the 22 Cal stuff. Thanks Bryan

 

[dmoran]

My way is to shoot them over a chronograph to establish a velocity average.
Then shoot them at a couple distances and use reverse ballistics to tell me what the BC come out to be for that Lot of bullets and in that rifle barrel. Simply by adjusting the BC value in the ballistic program until the ballistics line up to the actual impacts on the targets. The BC value established is the true BC to my unique scenario, bullets, and rifle. More so then any advertised BC value.
My 2-cents
Donovan

 

[XTR]

My way is to shoot them over a chronograph to establish a velocity average.
Then shoot them at a couple distances and use reverse ballistics to tell me what the BC come out to be for that Lot of bullets and in that rifle barrel. Simply by adjusting the BC value in the ballistic program until the ballistics line up to the actual impacts on the targets. The BC value established is the true BC to my unique scenario, bullets, and rifle. More so then any advertised BC value.
My 2-cents
Donovan

If you use this method make sure you have good atmospherics, and use a known zero (say 100 yards) and the use the measured drop from point of aim on a target at distance (say 300 to 600 yards) not your scope come ups. Not all scopes move what they say they do. Donovan, I'm not not implying that you don't do it this way, but I've seen some ridiculous MV claims over the yrs that were based on scope come ups in ballistics programs.

 

[dmoran]

XTR -
Accurate ambient is crucial for any factual testing and/or ballistics. As is corrected turret values and accurate Zero's.
Personally I use 2 infrared chronographs on a 8' rail at the muzzle and a acoustic at the target(s).
Donovan

 

[Bryan Litz Ballistics]

I've not tested the 175 TMK yet, but I have tested the 155 TMK. It's BC is practically identical to the 155 SMK Palma (2156) bullet.

-Bryan

 

[liltank]

I've not tested the 175 TMK yet, but I have tested the 155 TMK. It's BC is practically identical to the 155 SMK Palma (2156) bullet.

-Bryan

Would the 175's be on the to do list by chance?

 

[Bryan Litz Ballistics]

Yes, I would just need samples. Are they in stock anywhere yet?

 

[liltank]

Yes, I would just need samples. Are they in stock anywhere yet?

I bought mine from Grice Gun Shop in Clearfield,PA.

 

[Bryan Litz Ballistics]

Does Dudly still work there?

 

[liltank]

Does Dudly still work there?

Not sure. I live an hour south of Clearfield. Never an avid shopper there, but they usually have reloading supplies I'm looking for. I just happen to be there when they got there first shipment of TMK's in. How many bullets would you need?

 

[Down South]

I've not tested the 175 TMK yet, but I have tested the 155 TMK. It's BC is practically identical to the 155 SMK Palma (2156) bullet.

-Bryan

Wow, so the BC numbers are much lower for the 155 TMK than what they say they are?

 

[wolley]

Bryan, The BC numbers you got were for the non-pointed(factory pointed) 2156? If so that says quite a bit about Sierra's marketing hype.

 

[XTR]

....but I have tested the 155 TMK. It's BC is practically identical to the 155 SMK Palma (2156) bullet.

-Bryan

I'm not surprised, but disappointed that the manufacturer seems to have significantly over reported the BC.

Just running the numbers in JBM assuming some standard atmospherics and elevation comparing the 2156 and the TMK, the TMK calculates to having 22.5 inches less drop and 12.4 less windage at 1000 yards in a 10MPH cross wind.

I've got 300 155 TMKs to play with, I guess I need to get some 2156s to load in similar loads and shoot side by side.

 

[Bryan Litz Ballistics]

Bryan, The BC numbers you got were for the non-pointed(factory pointed) 2156? If so that says quite a bit about Sierra's marketing hype.

The 2156's I tested were factory pointed; they have the same BC as the 155 TMK:
http://appliedballisticsllc.com/BulletDataFiles/BPofRB_Final%20Extract%20Pages%20277.pdf

The exact BC/Velocity breakdown isn't exactly the same, but the average from 3000 to 1500 fps is practically identical.

I would need at least 20 bullets to test (of the 175 TMK). I prefer to purchase them but can't find them in stock anywhere.

-Bryan

 

[Park ranger]

Bryan, in your book applied ballistics for long range shooting, sierra 2156 is listed as having a g7 bc of .229. The file you attached list the 2156 as g7 of .237. Did further test revel a higher bc, or did sierra change something? Thanks!

 

[Erud]

I'm (definitely) not Bryan, but I'd bet the difference is between the non-pointed 2156's in the original book, vs. the current production pointed version.

 

[minnesotamulisha]

Hi Gents. Maybe a little off topic, but if the 2156 Palma has a nearly identical BC to that of the TMK, where lies the advantage?

 

[Berger.Fan222]

Hi Gents. Maybe a little off topic, but if the 2156 Palma has a nearly identical BC to that of the TMK, where lies the advantage?

It depends on your use and what "nearly identical" really means.

In general, plastic tipped bullets have greater uniformity in BC than traditional SMK tip designs. This means that the drop and wind drift will be closer to the same, all other factors being equal.

Also, looking at the Sierra BC numbers, the TMK has a G1 BC of 0.519 for most of the trip out to 600 yards. The 2156 Palma bullet has a G1BC of 0.470 for most of the trip out to 600 yards, assuming a muzzle velocity of 2800 ft/s. The difference may be smaller for muzzle velocities (closer to 3000 ft/s) and the range of velocities typical for 1000 yards, but Sierra's numbers suggest a significant BC advantage for midrange use. The BC advantage works out to about 0.6 MOA less wind drift at 600 yards under standard conditions and a 10 MPH cross wind.

Finally, in most designs a plastic tip helps initiate reliable and violent expansion in game animals and varmints over a wide range of impact velocities compared with traditional SMK designs.

 

[kyreloader]

Hi Gents. Maybe a little off topic, but if the 2156 Palma has a nearly identical BC to that of the TMK, where lies the advantage?

It depends on your use and what "nearly identical" really means.

In general, plastic tipped bullets have greater uniformity in BC than traditional SMK tip designs. This means that the drop and wind drift will be closer to the same, all other factors being equal.

Also, looking at the Sierra BC numbers, the TMK has a G1 BC of 0.519 for most of the trip out to 600 yards. The 2156 Palma bullet has a G1BC of 0.470 for most of the trip out to 600 yards, assuming a muzzle velocity of 2800 ft/s. The difference may be smaller for muzzle velocities (closer to 3000 ft/s) and the range of velocities typical for 1000 yards, but Sierra's numbers suggest a significant BC advantage for midrange use. The BC advantage works out to about 0.6 MOA less wind drift at 600 yards under standard conditions and a 10 MPH cross wind.

Finally, in most designs a plastic tip helps initiate reliable and violent expansion in game animals and varmints over a wide range of impact velocities compared with traditional SMK designs.

First, Bryan tested the tipped versions of the 2156s, so alleviating some of the improved uniformity of using a plastic tip of the TMK.

Second, the whole argument is that the BCs of the two bullets are almost identical (over all velocities), therefore showing no BC advantage for any distance.

Lastly, I agree the TMK might aid in expansion.