Sierra Heavy TMK 6MM Testing

[coya]

Is your 107 load with imr4350 also? Do you mind sharing what it was?

107 tmk/108 eldm
Imr4350 41.9gr
2.800
107 tmk 2982fps
108 eldm 2983fps

Both shoot a 1.5 inch group

 

[brucemt]

107 tmk/108 eldm
Imr4350 41.9gr
2.800
107 tmk 2982fps
108 eldm 2983fps

Both shoot a 1.5 inch group

Thanks coya, appreciate it

 

[coya]

Tried the 116's a touch hotter at 41.0 grains of imr4350 and the gun didn’t like it. Gonna keep the 40.6 load and just let her be a "good gun"

 

[Hurley88]

Ok, rooouuugh mock-up (time constraints & not using this gun with the 116 TMK), but here goes.

I didn’t disassemble the bolt for a real Wheeler test, didn’t use bullet seater with microneter adjustment, just did it by feel and measured as I went. So don’t trust my numbers, I just didn’t want the bullet rammed into the lands.

Looks like when seated to mag length in M+ mags, the neck grabs the whole bearing surface of the bullet and the jump distance is somewhere around 0.088–0.116” (like I said, rough).

I’ll be out in the morning hopefully to shoot some and post velocities. Will do as I usually do, just a half grain difference per round and record the velocity. First sign of any pressure, I subtract a grain and call that max. I’ll post up here if I can get ‘em done.

 

[coya]

Tried the 116's a touch hotter at 41.0 grains of imr4350 and the gun didn’t like it. Gonna keep the 40.6 load and just let her be a "good gun"

Forgot to mention, this load shot 2910fps

 

[Hurley88]

Tikka 243, 16” McGowan barrel, Starline Brass, 116 TMK. Seated to mag length in M+ magazines.

H4831SC
42.5: 2542
43.0: 2599
43.5: 2611
44.0: 2639
44.5: 2689

H4350
39.0: 2608
39.5: 2630
40.0: 2665
40.5: 2696
41.0: 2726

No stiff bolt lift or discernible differences in primers or case head. But this was shaded, breezy, and 66 *F so not a scorcher. 740ft elevation. I would caution anyone at around 40.5 H4350 or 44.5 H4831; the best determiner of pressure we currently have is velocity, and the 2650-2690fps range seems to be the red zone for this barrel length from all the similar reloading data I could find. Those numbers would be 2770-2790 for 20” barrels and 2890fps for 24” barrels.
I’m not the type to push the envelope, I’d just build a PRC or put a longer barrel on if I wanted more.

But, there’s some data for everyone. Good luck guys! Ima get back to what I came here for haha

 

[Willie IV]

First time reloader here and have a quick question with the 107 TMK.

6CM Tikka with 250 rounds down the pipe so far.

After a thorough cleaning and borescope verified, I measured to the lands and came up with CBTO of 2.280. Pictured is a seating depth of .020" jump with a COAL of 2.900". Fits my mag and chambers fine.

Is that enough bearing surface inside the neck?



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[mlevimadden]

First time reloader here and have a quick question with the 107 TMK.

6CM Tikka with 250 rounds down the pipe so far.

After a thorough cleaning and borescope verified, I measured to the lands and came up with CBTO of 2.280. Pictured is a seating depth of .020" jump with a COAL of 2.900". Fits my mag and chambers fine.

Is that enough bearing surface inside the neck?

View attachment 1041101

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Rule of thumb is minimum of one bullet diameter (0.243”) of bearing surface in the case neck.

 

[Hurley88]

Most would say yes, I would tend to disagree.

If you’re asking will they shoot? Yes they will.

 

[Willie IV]

If I seated to 1 diameter deep I'd have approximately. 140 jump.

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[ID_Matt]

If I seated to 1 diameter deep I'd have approximately. 140 jump.

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That’s about where i seated mine and they shoot just fine. Right at the boat tail/neck shoulder junction. 1” or less for 10 rounds with H4350.

 

[Frozenlead]

As long as they’re out of the lands, I’ll generally load around the neck shoulder junction and send them.

 

[Hurley88]

If I seated to 1 diameter deep I'd have approximately. 140 jump.

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Don’t get too hung up on jump distance. Mine are jumping 0.185” and right around 1” 10-shot groups