6 Grendel 107 SMK Load data

[Lawrence97]

21702884-E890-47FC-9830-A7AA3D06F381.jpeg

[A5BLASTER]

What's the jump?

[VASCAR2]

https://bergerbullets.com/product/6-mm-105-grain-bt-target/

[Lawrence97]

I am jumping .027-.030 so that I can get 2.260 COAL to fit in my magazines.

[VASCAR2]

https://www.hornady.com/bullets/rifle/6mm-.243-108-gr-eld-match#!/

[Lawrence97]

[Klem]

Lawrence,

What range were you shooting those groups? If this is 100yds then it looks normal for an average barrel. TBox with bolt is at the top end of pricing however so I would expect it to perform as well as a Lilja, Bartlein or Kreiger. We don't hear much about TBox on the forum. Maybe the 107 doesn't like the fast 1:7.5 twist given the norm is more 1:8.

Your extreme velocity spreads will not be the fault of the bullet and may be something else like neck tension. The second group with two groups of two holes could be not enough neck tension in an auto loader. The cartridge slams into battery and the bullet continues on into the lands. This then causes a pressure spike and higher MPI. Do you know your neck tension (a common standard is .004" for auto loaders).

Regardless of the velocity data a couple of those groups look actually pretty good. Have you had much experience with an AR? It is certainly not an 8kg heavy barrel F-Class gun with 3" wide parallel tracking stock.

[Lawrence97]

Klem,
The groups were shot at 100 yards. My barrel is a 1-8 twist. Neck tension used was .003. My experience with an AR is extensive with the platform as a .223.
I will look into adding neck tension and testing with a 105 VLD.

Thanks.

[grayfox]

Not for the 6 Grrr but another 6mm (1:7.7), I found myself gravitating to the 105 HPBT hornady and 103 Eldx... even though a hunting bullet - not as twist sensitive. Sounds like you have a lot more experience than I but like Vascar my 2 cents' is maybe look at a couple other bullets.

[Lawrence97]

9AEF9E05-FEFB-47C2-BCBC-AEC8AEBF0626.jpeg

[LtDan]

Anything over 105 is pushing the 6 Grendel/243LBC

[Lawrence97]

Has anyone had luck with the Sierra 95 SMK (NOT the Polymer tipped version)?

[grayfox]

I do want to put in one other suggestion for you which you might already be aware of. In your ladder testing of this case, whose capacity is close to that of the normal Grendel, I would limit my gr-increases to 0.3 max, mostly I use 0.2, ie, slightly less than 1% of case volume. A 0.5 delta lets you cover a powder range, true, but you could very well miss any nodes by passing right over them, grain-wise.

[CJW]

Interesting point Greyfox.

[Klem]

[ATTACH=CONFIG]15677[/ATTACH]

Lawrence,

The neck tension theory still holds true given the information in your latest photo.

If you look at the vertical bias of the first two groups; the H4895 and the 25gns of Comp there's no reason for this as you are obviously a shooter. The next giveaway is the first round low of the second group. This will have been fed into the chamber under control and therefore less chance of the bullet moving in the neck. The rest of the group will have been auto chambered with more violence. Bullets shift forward to kiss the lands and the start pressure spikes. I have experienced this myself and am also an F-Class shooter.

The MPI's getting lower on the target as the loads increase defies physics (see attached MPI calcs). I have no clue why you are shooting progressively lower as you load more powder in, all other things being equal.

Your group sizes of around the 1MOA mark for 4 careful shots is average for an average barrel.

Choosing a different bullet would seem the path of least resistance but I doubt it is the fault of the bullet. Vertical bias will follow you to the next bullet and haunt you - the data is not pointing at the bullet.