Sierra Heavy TMK 6MM Testing

[glock233]

I've shot the 116's twice now at distance to confirm what puzzled me on my first trip out.

The trued data I need to hit center at 1020 yards puts me 1 MOA (.3 mils) high at 700 yards.

I can't really make sense of that large of a discrepancy, but I've shot it twice now, once in the morning and once in the evening. Both times with good environmentals. Both times, same exact results.

That correction would put me at .31 G7 at 600-700 yards, and somewhere between there and 1020 yards it drops to a .28 G7. Just seems like a large drop. Not quite sure what to make of it, wondering if anyone else has any similar info?


The bullets also shot well on the last trip out. 5 shots into a .5 moa group at 622 yards and 4 shots into a .5 moa group at 1027 yards.

While projectiles do have different BC’s at different speeds, I’ve never seen that large of a discrepancy before.

It’s most likely to be “your rifle isn’t actually zero’d at 100 yards”, which can do stuff like that.

 

[43.6N]

I've shot the 116's twice now at distance to confirm what puzzled me on my first trip out.

The trued data I need to hit center at 1020 yards puts me 1 MOA (.3 mils) high at 700 yards.

I can't really make sense of that large of a discrepancy, but I've shot it twice now, once in the morning and once in the evening. Both times with good environmentals. Both times, same exact results.

That correction would put me at .31 G7 at 600-700 yards, and somewhere between there and 1020 yards it drops to a .28 G7. Just seems like a large drop. Not quite sure what to make of it, wondering if anyone else has any similar info?


The bullets also shot well on the last trip out. 5 shots into a .5 moa group at 622 yards and 4 shots into a .5 moa group at 1027 yards.

tip melting?

 

[Lawnboi]

7.5 twist

I wonder how much BC degradation your seeing that much just be too little to notice at 700.

 

[huntnful]

While projectiles do have different BC’s at different speeds, I’ve never seen that large of a discrepancy before.

It’s most likely to be “your rifle isn’t actually zero’d at 100 yards”, which can do stuff like that.

I agree. But that’s not the case here. Zero checked before both outings.

Dialed down .25” after this 10 shot zero.

 

[huntsd]

In my experience with the 107 tmk in a 243 tikka, I’m building my loads of of the listed max for the 108 Eldm. In my experience it builds pressure with less powder then the 107 tmk. I loaded up some 107s to 48.3 grains of h1000 and I’m also going to try 41 grains of h4350.

I am still a pretty novice reloader but I had an ejector ring at 39.7. Didn’t notice till I got back. So I shot 40.6 while there and it didn’t have a sign from what I could tell. Not sure why this would happen.

 

[huntnful]

I wonder how much BC degradation your seeing that much just be too little to notice at 700.

Yeah it’s just weird for that large of a drop off. Basically blamed it on myself the first time.

Then went out to verify again and had the exact same impacts. It’s show a 1.41 SG which isn’t terrible. Could just be causing issues in this specific instance though

 

[blacktailcentral]

Yeah it’s just weird for that large of a drop off. Basically blamed it on myself the first time.

Then went out to verify again and had the exact same impacts. It’s show a 1.41 SG which isn’t terrible. Could just be causing issues in this specific instance though

Are you shooting in a canyon??

 

[huntnful]

Are you shooting in a canyon??

No it's flat as can be.

Also trued my other gun which is shooting a 144 LRHT at 3110fps and the same data it needed for center hits at 622 yards was spot on at 1027 yards.

 

[B_Reynolds_AK]

7.5 twist

You wouldn’t think it would be that far off with how fast you’re shooting them, but Sierra does say 1/7 for them.

 

[blacktailcentral]

No it's flat as can be.

Also trued my other gun which is shooting a 144 LRHT at 3110fps and the same data it needed for center hits at 622 yards was spot on at 1027 yards.

Forsure, just asking because ive seen updrafts/downdrafts do some crazy things before. Whats the sd/es??

 

[huntnful]

You wouldn’t think it would be that far off with how fast you’re shooting them, but Sierra does say 1/7 for them.

I agree. And .31 G7 working at 700 yards but dropping to a .28 G7 after only another 300 yards just seems fishy.

 

[huntnful]

Forsure, just asking because ive seen updrafts/downdrafts do some crazy things before. Whats the sd/es??

Definitely. ES of 19fps for 10 shots

 

[Porthunter]

I agree. And .31 G7 working at 700 yards but dropping to a .28 G7 after only another 300 yards just seems fishy.

That seems extreme.

Now I’m slightly concerned about the 7.5 twist barrel I got for mine.

 

[wy_will]

Seems like a lot of folks are running around 41 or 41.5 each 4350 for the 107 TMK in the sixth Creed. I’m looking at GRT, and 42.5 isn’t even at pressure. Wondering if I am missing something?

41.5 has no pressure signs. I’m gonna try 42 and 42.5, but wondering why others not pushing similar?


Sent from my iPhone using Tapatalk

I saw ejector marks at 40.5gr of H4350 out of my PBB 20” tikka using Peterson SRP brass and CCI450s. This was with the 107 TMK at 2850fps

 

[eric1115]

Help me understand the stability question...

Velocity decays faster than RPM. SG should increase as you get further downrange, leading to a smaller SG driven loss of BC as you get further and further out. What am I missing?

I get that BC decreases with velocity decay, but that's a product of the CD/mach number curve, not dropping SG, right?

 

[passinggas33]

I’m bummed hearing that my 1.7.5 6UM barrel might not be ideal for these 116TMKs.

 

[Woodsman44]

Yeah me too. Just fire formed 100 6UM brass planning on 116TMK at 7.5 twist. If the 116’s don’t do well, I guess the next best option is the 107’s?

And have never done a deep dive into twist rate, BC, SG, etc. for picking the right combo. A quick lesson would be helpful


Sent from my iPhone using Tapatalk

 

[huntnful]

I wouldn’t panic guys. It’s RIGHT at the edge of full stability in a 7.5 twist at sea level. Adding much elevation will stabilize it fully.

Something could very easily be askew in my system, which is why I’m just asking if anyone else has seen such a drastic drop.

I need to go over my data entries again just in case

 

[Lawnboi]

Yeah me too. Just fire formed 100 6UM brass planning on 116TMK at 7.5 twist. If the 116’s don’t do well, I guess the next best option is the 107’s?

And have never done a deep dive into twist rate, BC, SG, etc. for picking the right combo. A quick lesson would be helpful


Sent from my iPhone using Tapatalk

You want an SG of 1.5 at the lowest elevation, and lowest temps you might see. You also want under 300k rpm to not blow up bullets.


I’m curious on the actual stabilization of tipped bullets. Being that the tip is lighter I’m not sure the miller formula applies (per Hornady) completely. But if I run my numbers for a 109eld which is very similar in length to the 107 I’m still below with low MV rifle in sub zero temps.

 

[B_Reynolds_AK]

I agree. And .31 G7 working at 700 yards but dropping to a .28 G7 after only another 300 yards just seems fishy.

Playing with the Berger stability calculator, the 116 moving at 3100 fps at 1,000 DA in a 1/7.5 shows “Marginally Stable” (1.49 SG)

The same bullet at the same atmospherics going only 2700 from a 1/7 barrel shows “Stable” (1.64 SG)