Sierra Heavy TMK 6MM Testing

[Castle Rock]

My tikka 8 twist 223 shoots 75s, 80s, and 88s very well at sea level after some load development.
H 4895 and seating long is the key.

 

[mxgsfmdpx]

8 twist Tikkas have shot all the .224 bullets from
Hornady just fine. Lately there have been crappy lots of loaded ammo and different lots of bullets that won’t shoot as well. 88s for me have been the most inconsistent but these “problems” aren’t inherent to Tikka barrels. I’ve seen the same issues in 3 other make/model barrels from 7 twist to 8 twist.

Tikkas are a hammer forged true 8 twist and aren’t “slow” on average as some presume.

 

[Formidilosus]

The 80gr eldm has been accurate in my tikka 223rem 8” and 22creed(reamed out 223 8”) but the drops don’t line up well in a ballistic solver even when calibrated I’m sure due to a less than ideal stability rate. You have to shoot and get actual drops for every range. And I could certainly see how 8” twist tikka bbls might not shoot them well. I may just be lucky.

What solver are you using, and what BC?

 

[ACHILLES]

Shooter and AB although I rarely use AB now since they completely changed it because it freezes up on me constantly.

1.16 length
G7 .258

I see in the new AB library it shows
1.17 length
G7 .255
Although even if I did use those numbers it would not make up for the discrepancies I was seeing.

And I used 1.16 length because my lot of 80eldms measured 1.16”

 

[Formidilosus]

Shooter and AB although I rarely use AB now since they completely changed it because it freezes up on me constantly.

1.16 length
G7 .258

I see in the new AB library it shows
1.17 length
G7 .255
Although even if I did use those numbers it would not make up for the discrepancies I was seeing.

And I used 1.16 length because my lot of 80eldms measured 1.16”

Hmmm. I use Hornady’s G1 and it has tracked to 800 plus.

 

[ACHILLES]

I’m not sure what’s going on exactly I’ve just assumed it was the lower GSR . Because when I ran the same lot of bullets using the same length and bc in the same solver through a 20” ruger gen2 22arc 7” twist. Drops lined up almost dead on.

 

[Lawnboi]

The Miller stability calc doesn't do well with plastic tipped bullets. The Berger stability calc, for example, suggests that an 80gr .224" ELDM is unstable at 2700fps and 1:8" (SG 1.15). In reality an 80 ELDM is perfectly stable at this speed and there is no BC decay at distance.

The JBM stability calc uses a modified miller that accounts for tip length/density and gives answers that align much better with observed reality for tipped bullets (SG 1.47 for the above example)

Hornady goes on further on their bullets, stability is in the range table. It’s been said a 1.2-1.5 sg is okay but not ideal. We have to remember that our conditions dictate what is stable. I live at around 1500 feet, last week shooting sub zero degrees I was -2000ft DA.

My 8 twist shoots the 75eld great In the summer and leaves me with head scratchers in the winter

 

[wind gypsy]

Shooter and AB although I rarely use AB now since they completely changed it because it freezes up on me constantly.

1.16 length
G7 .258

I see in the new AB library it shows
1.17 length
G7 .255
Although even if I did use those numbers it would not make up for the discrepancies I was seeing.

And I used 1.16 length because my lot of 80eldms measured 1.16”

Hmmm. I use Hornady’s G1 and it has tracked to 800 plus.

80 ELDm is a wonky one in the whole AB vs Hornady BC values deal. AB has it marked as significantly higher BC than Hornady which is the opposite of how most of the AB values compare to hornady published ELD BCs. I'd see what dope is kicked out with hornady's values.

Looking at 75s and 80s side by side, the small gap in BC between them published by hornady makes more sense than the much larger gap in ABs numbers.

That said, i doubt going from .258 or .255 to .240 G7 is going to make much difference in dope until you get out a ways.

 

[Formidilosus]

80 ELDm is a wonky one in the whole AB vs Hornady BC values deal. AB has it marked as significantly higher BC than Hornady which is the opposite of how most of the AB values compare to hornady published ELD BCs. I'd see what dope is kicked out with hornady's values.

Looking at 75s and 80s side by side, the small gap in BC between them published by hornady makes more sense than the much larger gap in ABs numbers.

That said, i doubt going from .258 or .255 to .240 G7 is going to make much difference in dope until you get out a ways.

AB’s data is always janky with Hornady bullets. I’m not sure if I have used one bullet from Hornady and had AB work, but yet it is at longer ranges.

 

[TimberHunter]

If you want an accurate stability rating with tipped bullets use the Jbm stability calculator that accounts for tip length of bullets and you can find the plastic tip lengths in jbm’s bullet library. I believe your line of thinking is correct. Because if you run the stability rate in a standard calculator with a tipped bullet it will give you a lower SGR than if you run it in jbm’s calculator that accounts for tip length.

Dumb question, what are you guys siding for the pressure input? Rule of thumb for every 1000’ about sea level?

Usually I enter DA or elevation plus temp


Sent from my iPhone using Tapatalk

 

[ACHILLES]

Dumb question, what are you guys siding for the pressure input? Rule of thumb for every 1000’ about sea level?

Usually I enter DA and temp or pressure, humidity, temp, and elevation.


Sent from my iPhone using Tapatalk

Siding for pressure input? I’m not sure what you’re asking.

Generally solvers are set up to run DA and temp or Elevation, pressure(HG), humidity, and temp.

 

[Jordan Smith]

I’m not sure what’s going on exactly I’ve just assumed it was the lower GSR . Because when I ran the same lot of bullets using the same length and bc in the same solver through a 20” ruger gen2 22arc 7” twist. Drops lined up almost dead on.

SG between 1.0-1.5 is, in general, giving up ~3% in BC value per 0.1 in SG under 1.5. It makes sense that you're getting more drop than predicted using BC values that assume a well-stabilized bullet.

 

[Jordan Smith]

Elevation, pressure(HG), and temp.

Elevation is irrelevant if you use absolute (gauge) pressure instead of relative (barometric pressure).

 

[pathnz]

Hmmm. I use Hornady’s G1 and it has tracked to 800 plus.

I use Hornady's G7 and it's spot on

 

[ACHILLES]

SG between 1.0-1.5 is, in general, giving up ~3% in BC value per 0.1 in SG under 1.5. It makes sense that you're getting more drop than predicted using BC values that assume a well-stabilized bullet.

I don’t remember if my drops were off by hitting higher or lower than predicted. But I agree it’s best to stay above 1.5SR for solvers to predict drops precisely but some don’t seem to have issues.

Elevation is irrelevant if you use absolute (gauge) pressure instead of relative (barometric pressure).

Your correct, I worded it poorly but edited it now. Meant to say you have to use DA and temp “OR” elevation, temp, pressure, and humidity.