Puzzled by POI Shift with Wolf Steel Case Grendel

[Hansel&Grendel]

Here is the rifle set-up:

• 16" Criterion 6.5 Grendel bored by Mark at PF
• Primary Optic: Sig Tango4 4-16x (stellar performer)
• Just added an Atibal MRD V2 4MOA RDS for CQB (similar to a Vortex Venom)
• The Atibal is solidly mounted on a Magpul 1:00 offset mount (no movement)

Here is the dilemma. I zeroed the Atibal at 25 meters just like an Aimpoint T-2, bench-rested on sandbags albeit canted 45-degrees, resulting in about a .75" group. I then shot free-standing at 25 meters canted at 45-degrees and noticed an eventual POI shift to the left of a few inches, still using Wolf steel-case.

Puzzled, I switched to Hornady Black and was rather shocked that POI using the same zero with 3 rounds was 5.5"L and 2.5"H in a very sloppy group, while bench-rested. I re-zeroed the Atibal with the remaining Hornady Black (about $6 later) and had a .5" group at 25 meters, still bench rested.

I also have a 6.5G SBR 11.5" Criterion with a Vortex Razor-E 1-6x. I consistently hit tight center-mass free-standing from 20-50 yards at 1x using Wolf steel case; any flyers are operator error.

My concern is if the Atibal is losing zero due to a defect. Or, is it possible for POI to shift that dramatically (5.5"L and 2.5"H) going from Wolf steel case to Hornady Black using the same zero, only at 25 meters?!

Cheers, Hans

[Bigs28]

Hornady american gunner shoots 3.5" lower then my hand loads.

[Double Naught Spy]

As I read your description, I did not see where any of your shooting was replicable. You changed shooting circumstances and changed ammo while comparing between rifles.

First, if you are comparing group size and POI locations, the rifle should be shot in the same manner each time. Why? It rules out all sorts of variables that you may introduce by shooting different ways. Ideally, you should make comparisons back to back during the same session so as to rule out a bunch of other variables (temp, wind, bumped scope, etc.).

Second, there is no reason to assume that any two variants of ammo will shoot to the same POI despite the rifle being zeroed. I sometimes have loads that shoot to the same POI and sometimes they are way off. Bigs28 mentioned American gunner shooting low. It does for me as well. Reloaders will do precise micro changes in powder loads using the same bullet and get different POIs and group sizes when shooting with the same rest in the same session (back to back).

I suspect the POI change between rested and standing is shooter introduced and not a defect of the scope or the ammo. The way to test that is the shoot different sets in the same manner. When you went to standing and shooting offhand and got a different POI, what you should have done is immediately return to the bench and repeat the shots that you did when you got your first group off the bench. If the POI remains as it originally was, then YOU introduced the change in POI such as by flinch, yank, etc. Also note that you may want to try your testing with a vertical gun, NOT canted. Check that it is vertical with a level. Don't worry about zero, but POI and group sizes.

Third, just to note, because one gun likes X brand or model of ammo does not mean Y gun will shoot it as well. Comparing between your two rifles does not actually address the problem of the potential problem with the sight on one rifle.

[Hansel&Grendel]

Good points DNS and Bigs28. I did replicate the bench shooting in the same manner all in one session at an indoor range, i.e., very controlled environment and very stable platform. My major concern was (is) the very different POI because it was only 25 meters with the same set zero, thinking that not much trajectory difference should happen in that short distance despite two very different loads (100gr steel case vs. 123gr ELD Match). At 100 yards yes, but not so much at 1/4 that distance.

The free-standing shooting could have easily been me because of the canted angle. Those shots were noticeably off but actually acceptable for the purpose of the offset micro RDS. This is a long-distance gun with an offset RDS micro for "just in case". I will do additional test fires between the loads. Thanks again.