Sierra Heavy TMK 6MM Testing

[khuber84]

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Post in thread 'Sierra Heavy TMK 6MM Testing'

Dec 21, 2025

This is in your Seekins 6 CM correct? If so, SAAMI freebore of .183.

Seated at .080 off, where does this put the boat tail to shoulder junction in the case?
Wondering if a longer fb, such as the PVA Standard (.210) might optimize these even more.

Any chance you could take a photo of a loaded round with a bullet lined up next to it?

@khuber84 I think a short 6 CM slinging these 117’s at 2800-2850 would be absolutely phenomenal.

Apologies for the terrible lighting. This is seated at a .085" jump, but this barrel also has over 1400 rounds on it. My typical...

• Carl Ross

• 

I did. There was no COAL listed. I figure 1400RDS of 6cm would likely have 40-70k throat erosion depending on how it was ran, powder used and what not.

 

[Carl Ross]

I did. There was no COAL listed. I figure 1400RDS of 6cm would likely have 40-70k throat erosion depending on how it was ran, powder used and what not.

It's 2.900" give or take. H4350 is the only powder, mostly pedestrian loads, sometimes ran hot-ish.

 

[khuber84]

It's 2.900" give or take. H4350 is the only powder, mostly pedestrian loads, sometimes ran hot-ish.

Thanks Carl! Appreciate you getting that info!

 

[PathFinder]

Testing on paper with the 243 Improved today at 500. Similar results between the three overall, with a little BC difference showing up.

Sent from my Pixel 10 using Tapatalk

 

[Formidilosus]

115gr TMK, 6UM. Shot in about a minute total. Barrel/suppressor mirage comes quick with the UM.

 

[Finaddictions]

115gr TMK, 6UM. Shot in about a minute total. Barrel/suppressor mirage comes quick with the UM.

View attachment 997875

You seem like you’re liking the 115’s best. Is that where you’re leaning? In my test batch, I thought the 116’s outshot both the 115& 117’s. I only shot them to 800, but have been pleasantly pleased, but the 116’s have been my favorite.

Have some of the 117’s loaded to hunt with this week, although I don’t think there will be any surprises. Expect them to work perfectly.

 

[HighUintas]

I'd probably prefer whichever one (out of 115-117) that is easiest to get to shoot accurately in the most chambers. I can't imagine any of them not being sufficient from a terminal perspective and wouldn't think there could be a big enough BC difference for it to have much impact in the final decision.

 

[43.6N]

Can you guys share anything about when Sierra wanted the feedback from your T&E?

Was it a “hey try these out and get back to us when you can” type of situation? Or more of a defined testing timeline?

 

[Finaddictions]

Can you guys share anything about when Sierra wanted the feedback from your T&E?

Was it a “hey try these out and get back to us when you can” type of situation? Or more of a defined testing timeline?

Sierra didn’t give any hard deadlines, but they want feedback sooner than later. I think they plan on running the bullets sometime this quarter, so it’s not open ended.

 

[Formidilosus]

Today. @Ryan Avery and @Superior Gun Works

6UM. Using Ryan’s brass which my gun did not like.


116gr-



117gr-




MRC 6cm. (Note had to use truck headlights to shoot)-

116gr-



117gr-





Both guns are +/- 8lbs all up and averaged right about what they do with any load/bullet.

 

[Formidilosus]

You seem like you’re liking the 115’s best. Is that where you’re leaning? In my test batch, I thought the 116’s outshot both the 115& 117’s. I only shot them to 800, but have been pleasantly pleased, but the 116’s have been my favorite.

Have some of the 117’s loaded to hunt with this week, although I don’t think there will be any surprises. Expect them to work perfectly.

They all are shooting well generally. However, the 115’s have been the most consistent from gun to gun and at distance overall.

 

[Finaddictions]

They all are shooting well generally. However, the 115’s have been the most consistent from gun to gun and at distance overall.

That’s super interesting. I’ve only shot them through 2 rifles, but I found the 116’s seemed to have the edge, but all 3 shot very well. Really splitting hairs though because at 100 all 3 averaged close to 1/2 minute for 10 shots but we’re closer to 1 minute at 600 & 800 yards. Need to try one more round of testing at distance.

 

[Bluumoon]

Today. @Ryan Avery and @Superior Gun Works

6UM. Using Ryan’s brass which my gun did not like.


116gr-
View attachment 998710


117gr-
View attachment 998711



MRC 6cm. (Note had to use truck headlights to shoot)-

116gr-
View attachment 998712


117gr-
View attachment 998713




Both guns are +/- 8lbs all up and averaged right about what they do with any load/bullet.

Is that a light load of H4350? Makes me think these heavies may not be the choice for 6CM and the 107 (or 95) may be more useful.

 

[Castle Rock]

Most of the groups that are shown here are well over moa which is pretty disappointing to me

 

[jonnyviceroy]

Most of the groups that are shown here are well over moa which is pretty disappointing to me

At least it’s not cherry picked three shot groups (if I do my part quarter moa all day shooters) like most people tend to post. Also group size is overly focused on when it has lesser impact on hit rates than other critical factors.

 

[atmat]

Most of the groups that are shown here are well over moa which is pretty disappointing to me

Why? That’s a good 10-shot group.

 

[Kaleb]

Most of the groups that are shown here are well over moa which is pretty disappointing to me

Look at Finnaddiction's results. He's getting half moa.

 

[Formidilosus]

Is that a light load of H4350? Makes me think these heavies may not be the choice for 6CM and the 107 (or 95) may be more useful.

? I don’t know how you come to that conclusion. None of my groups are worked up loads at all. They are middle of the road safe and just loaded.

The only thing that I have checked so far is:

1). Are they finicky to load, sensitive to seating depth, etc. (like the 95gr TMK)

2). BC.

 

[Nine Banger]

Is that a light load of H4350? Makes me think these heavies may not be the choice for 6CM and the 107 (or 95) may be more useful.

I bet they're going to be great for a quick drop compatible load in 6CM with H4350. I had to cram H1000 in to get 115's to fly with QD.

 

[Formidilosus]

Most of the groups that are shown here are well over moa which is pretty disappointing to me

Shooting 12x ten round groups (120 shots), from 4 different 8-9 +/- pound all up rifles, with three different bullets, with zero load work up done- middle of the road powder charge and dump it, seat boattail at neck/shoulder, and shoot; with the largest 10 round group being 1.2 MOA- and that’s disappointing?

That’s not counting IIRC 27 of 29 total shots across four days that hit a 14.5” tall target at 985 yards, 1,005 yards, and 1,025 yards.