Sierra Heavy TMK 6MM Testing

[Schmo]

The sierra site says available mid-March and given their availability issues in the past I would assume even that date is optimistic.

I’m hopeful that the new leadership will be able to hold to that timeline

 

[KyleR1985]

Based on my correspondence with Sierra, I would expect staggered delivery of the new TMK’s, following which ones get design/testing done first.

While I can’t speak to when bullets actually get produced and shipped - 6mm 107’s and 6.5mm 153’s will get run first, with .25’s, 6mm 116’s, and .22 88’s to follow loosely in that order.

 

[wind gypsy]

131 TGK might be a nice bullet for fast quarterbores too.

 

[Schmo]

131 TGK might be a nice bullet for fast quarterbores too.

Gross

 

[dreamingWest]

Any chance a 10 twist 243 would stabilize the 107s?

 

[Carl Ross]

Any chance a 10 twist 243 would stabilize the 107s?

You’d have a decent chance…at 12,000 ft in July.

For general use, no.

 

[eric1115]

Any chance a 10 twist 243 would stabilize the 107s?

No, especially if they are as slippery as advertised. 95 TMK is your huckleberry.

 

[wind gypsy]

No, especially if they are as slippery as advertised. 95 TMK is your huckleberry.

Even that might be marginal. Sierra calls for 1:9 min twist.

 

[eric1115]

Even that might be marginal. Sierra calls for 1:9 min twist.

That's true, but it does seem like they set that twist spec to be able to shoot a 6x45 in Death Valley at -20°F.

Still, @dreamingWest you should probably buy 100, not 1k to start.

 

[dreamingWest]

If I end up with 10 twists 243s, I'll just stick with NBTs.

I'm shopping a lefty 6mm for my son and a righty for myself this year. I'm hoping for easy button no gunsmith necessary options from Tikka or Browning. Watching Shot Show releases this week.

 

[blacktailcentral]

131 TGK might be a nice bullet for fast quarterbores too.

How much of a difference in expansion between the tgk and tmk?

 

[24valve]

Even that might be marginal. Sierra calls for 1:9 min twist.

Sample size of 1, but we've shot 95 TMK's out of a 1-10 Tikka 243 with no stability issues in the mountain west.

 

[24valve]

How much of a difference in expansion between the tgk and tmk?

I'll preface this having only shot elk, deer, and antelope with TMK's but I understand that there is a very large difference. TGK's have a much tougher jacket, which means that they expand and fragment minimally, but penetrate deeper compared to TMK's.

Here is a link to the 6mm success thread to someone with firsthand TGK experience: "Entrance was caliber size and exit was probably a one inch hole." A friend of mine killed an elk with them this past fall and this was his experience as well.

Post in thread '6mm /.243 hunting success on Big Game'

Dec 4, 2025

I didn't take any more photos after I started processing it. Entrance was caliber size and exit was probably a one inch hole. There was a very good blood trail. We have 10-15 kills with the 90s and 6.5 130s with great results. Most of our shots are 200 yards and in though.

• Mrwoodard

 

[Jordan Smith]

I'll preface this having only shot elk, deer, and antelope with TMK's but I understand that there is a very large difference. TGK's have a much tougher jacket, which means that they expand and fragment minimally, but penetrate deeper compared to TMK's.

Here is a link to the 6mm success thread to someone with firsthand TGK experience: "Entrance was caliber size and exit was probably a one inch hole." A friend of mine killed an elk with them this past fall and this was his experience as well.

Tough to make an assessment based on a small sample size. I've seen similar performance (caliber entrance, 1-1.5" exit) from various models of the ELD-M in multiple instances, as well, but that doesn't mean that the ELD-M and TGK are terminally equivalent, broadly speaking.

 

[eric1115]

I'll preface this having only shot elk, deer, and antelope with TMK's but I understand that there is a very large difference. TGK's have a much tougher jacket, which means that they expand and fragment minimally, but penetrate deeper compared to TMK's.

Here is a link to the 6mm success thread to someone with firsthand TGK experience: "Entrance was caliber size and exit was probably a one inch hole." A friend of mine killed an elk with them this past fall and this was his experience as well.

Post in thread '6mm /.243 hunting success on Big Game'

Dec 4, 2025

I didn't take any more photos after I started processing it. Entrance was caliber size and exit was probably a one inch hole. There was a very good blood trail. We have 10-15 kills with the 90s and 6.5 130s with great results. Most of our shots are 200 yards and in though.

• Mrwoodard

My understanding is that the jacket thickness and toughness are actually pretty similar between TMK and TGK, but the core is much harder due to more antimony (?) in the TGK. My TGK kills were enough different from my TMK kills (.308 165 TGK vs .223 77 TMK) that I can't say anything definitive based on first hand experience, but it was generally as most people describe. Narrow, almost mono style wound with the TGK and violent, wide carnage with the TMK.

 

[24valve]

My understanding is that the jacket thickness and toughness are actually pretty similar between TMK and TGK, but the core is much harder due to more antimony (?) in the TGK. My TGK kills were enough different from my TMK kills (.308 165 TGK vs .223 77 TMK) that I can't say anything definitive based on first hand experience, but it was generally as most people describe. Narrow, almost mono style wound with the TGK and violent, wide carnage with the TMK.

I can't speak to the hardness of the lead core, but the jacket thickness and tip opening is not the same between the two.


(I did not cut these open, just found this cross section on the internet)

 

[eric1115]

I can't speak to the hardness of the lead core, but the jacket thickness and tip opening is not the same between the two.

View attachment 1007983
(I did not cut these open, just found this cross section on the internet)

I stand corrected! I could have sworn I saw a cross section of a TMK and TGK side by side (thought it was the 90 and 95 6mm's) that showed very similar jacket thicknesses. Thanks for the info!