Sierra Heavy TMK 6MM Testing

[IrkedCitizen]

Sideways impacting bullets already has the tumble initiated....

 

[Formidilosus]

Curious how the BC holds up in practice at extended distances, especially at low DA.

At 4,000ft DA .609 G1 is spot on at 800y in that rifle.

 

[Formidilosus]

What about the guys with bullets going sideways through the paper? Probably isn’t working for them lol

No. Which is why “DA and weather matters”. Not just blanket “you need X”.

An 8” twist at western US DA’s is not an issue at all. A 7.5” twist at -3,000ft DA was no issue either for two different barrels.

 

[Formidilosus]

Sea level on a cold day?

Probably not a good idea with an 8” twist. DA matters. 2x 7.5” twist barrels were just fine at -3,000ft DA back in February however.

 

[IrkedCitizen]

UM just posted on IG that they have 25cal 135gr, 7mm 185gr, and .22 77gr tmks in stock

 

[mustelid_master]

No. Which is why “DA and weather matters”. Not just blanket “you need X”.

An 8” twist at western US DA’s is not an issue at all. A 7.5” twist at -3,000ft DA was no issue either for two different barrels.

negative 3000ft DA?

 

[MEdude]

-3000 Happen on the coast of Maine every winter…

 

[Stocky]

I dont use 4dof for much but its useful for stability calc in the bullets listed which includes dtacs and heavy smks etc for comparisons. Its works on the actual point mass not the miller formula etc. Some stuff is way more stable than people realise. And cold temps make a massive difference.

Its usually pretty accurate in that if its above 1 in the expected conditions its should hit point first (the 1.5 Ive shot loads with an SG of 1.1 in our winter (negative DA) pretty regularly. In the field most places even we hunt at "low elevation" gives us enough boost to not notice issues with BC).

For example here's the 115 DTAC at sea level at 30F in an 8 and 7.5 twist and hornadys Notes on SG in 4dof.

 

[Jordan Smith]

I dont use 4dof for much but its useful for stability calc in the bullets listed which includes dtacs and heavy smks etc for comparisons. Its works on the actual point mass not the miller formula etc. Some stuff is way more stable than people realise. And cold temps make a massive difference.

Its usually pretty accurate in that if its above 1 in the expected conditions its should hit point first (the 1.5 Ive shot loads with an SG of 1.1 in our winter (negative DA) pretty regularly. In the field most places even we hunt at "low elevation" gives us enough boost to not notice issues with BC).

For example here's the 115 DTAC at sea level at 30F in an 8 and 7.5 twist and hornadys Notes on SG in 4dof.

View attachment 1083010View attachment 1083011View attachment 1083012

Most ballistic calculators approximate a point mass as the center of gravity without modeling the mass distribution of the bullet nor the rotational degrees of freedom, along with the aerodynamic properties that emerge. Hornady’s 4DOF isn’t modeling the full 6 degrees of freedom, but does include angle of attack to the 3 translational degrees of freedom and mass distribution, which is why it can derive Sg at each distance.

Note that Hornady mentions what Litz has also found phenomenologically, which is that supersonic drag is minimized at a muzzle Sg of about 2.0 (Litz reported a value of 1.5).