The test ammunition is the 75gr .223 gold dot.
The test optic is a Kahles K16i. It weighs 17oz, per product literature.
The mount, and subject of this test is a custom mount that Andrew Bobro made for me. It is a 30mm with 0MOA bias, and the lever on the RIGHT side. The clamping springs used are the heaviest Bobro stocks. It weighs 7.5oz, and is the single-lever version.
The rifle is a Daniel Defense with a 16.1" Chrome Lined, Hammer forged, .gov profile barrel. It is freefloated. The suppressor is a Surefire 556-212, mounted on a 212a mount. The trigger is a Geissele Super-V. The rifle will be fired with the front of the rail braced over a sand-bag.
The protocol for this test will be tailored to display RTZ (or lack) of the Bobro mount. It is as follows:
- After zeroing, two targets with 1" grid will be placed at 100 yards from me, the shooter. I will fire a 10-shot group without removing the optic into the target on the left. I will "come off of the gun" after each shot. This is because it is necessary to do so to remove the mount efficiently in the second string of fire, and will prevent the disruption of cheek weld being a potential discriminatory factor in over-all group size, or POI shift.
I will then fire 10 shots into the target on the right, removing the mount from the rifle between each shot. The first shot will be fired after removal and replacing of the mount.
The two groups will then be measured for over-all size, and any POI shift of the group centers will be noted.
The protocol was as described. Also, of note, I could see bullet holes clearly at 100 yards using the K16i. This agitated my spirit.
The largest single shift I could measure from the Bobro mount was 0.733 MOA. This was "high". It also negates to take into account that this is about a 1.5 MOA rifle/ammo combo, and I am typically a 0.5-0.75 MOA shooter on any given day, if using a bolt gun with quality ammo and optic off the bench. Statistically, I did not discern any POI shift that would concern me. Even if using our "largest extreme single measurement", we are off by roughly only 50% of the intrinsic accuracy of the platform. Put another way, at 1000 yards, you will "miss" by 7.33", at the absolute very worst, assuming perfect intrinsic accuracy of the system.
I do not think there is a 0.733 MOA shift in this system, if one were to use statistically significant data, which mine is not, because who's to say that 1 shot wasn't pulled 1/4-1/2"? I know when I really throw one (1 MOA+), but I can't call 1/4-1/2 MOA pulls. Also consider, the variance of total group size from the group without detachment vs. detachment each shot (including before the first was fired) varied by only 0.482 MOA.
Anyway, here is the raw data for your consideration. maybe someone with some software can upload the groups and give a "center" POI shift that appropriately weights the distribution of the 10 shots in each group:
*I would also note that I have been using my 1-4 NF in a Mil-Spec Unimount, torqued to 65 in-lb. I removed it for this test, and re-attached it afterward using a tq wrench. The RTZ confirmation showed no discernible shift. It still punched a tiny 3-shot group dead-on the bulls-eye. I did not care to perform a statistical analysis of it. It's "on", and that's fine.
Someone plugged in some data for me:
0.385 MOA shift of the group centers across 10 removals...
