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

 

[NW_backcountry90]

116’s grouped pretty good out of the 6 prc unfortunately didn’t get to the speed I wanted before hitting pressure, 59.5g of n570 was right round 3080 out of 21” barrel 60g getting slight halo was 3100, 60.5g halo and bolt lift 3130. Looks like I’m gonna roll with the 107’s tmk’s at 3250 I’m sure they will kill just fine hahah the 107’s grouped just like the 116’s I haven’t found a bullet this gun doesn’t like.