AR Positional POI Shift Test

[Veracity]

I've got 40 rounds loaded for the test. 6ARC
Lapua Grendel necked down
108 eldm
29.4 Lever
2.290 oal
should be 2670-2700 This barrel only has about 40 rounds on it. It is the replacement Rainier UM. If head space grows over these 50 rounds they can stick this barrel up their ass.

VLTOR Fusion F-15 Face trued & shimmed. The VTOR Fusion extension is just as loose as the MUR's
Steel KRG Arca rail
22" +2" gas barrel
Gun weight with Ckyepod & no mag is 15lbs-6oz.

I'm thinking 5 rounds to get a good zero @100y Bi-pod/rear bag & light preload, 5 more to true dope to waterline at 500y with same bi-pod rear bag. Then build and break position 5 x with 3 shots each from prone bipod/rear bag to kneeling off a barricade with a smedium heavy fill up against the magwell.

Does this sound like a reasonable test?
What is the preferred program you guys would suggest I use to calculate mean radius after this test??

500Y on paper will probably hurt my feelings. Hopefully the load will be at or under 1 moa at 100y

Thanks

Test sounds good. I am with @PBWalsh on shooting at 100y. External factors can skew the data at distance. Converting the measurements to MOA/MIL after verifying on paper over multiple groups is what I recommend. Try and shoot them how you normally would from bipod and barricade as to not skew data. If you normally load bipod then do that, however as an instructor I would recommend trying a more neutral position in the future

Hornady 4Dof and BallisticX are what I use for measuring groups. I typically go with Ballistic X as it's only function is to measure so it's quicker to knock out and more refined in my experience.

 

[Paris_Bulks]

The gun still has a gap between the magwell & the rail. For the poi shift flex must be happening across the joint where the extension mates to the upper. Seems like the steel rail may actually aggravate the issue since it's heavy. In addition to the heavy Arca, I've got a few weights out towards the front of the rail.
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The range I'll be shooting at for this has 100 & 500 only.
I could just shoot dots @100y, but I'd still want to enter them all into some program to calculate mean radius from dot center for the total group of 15 per position. Not sure what tool/program is best suited to do that?

Your thinking is correct. I've tested positional vertical shift with my LAM through my day scope on a wall at dusk at 200 yards and the shift is greater (.2 mil more) when I have a bipod hanging on the end of the rail.

 

[357Max]

I shot for shift today.

3 rounds prone - 3 rounds bagged tight to magwell x 5 cycles
On the last round prone I shot 1 at small dot upper left, same for bagged, but I dialed U.3 & L.2mil.

There is definite shift, but I certainly had a bit of wobble of the bag. Grip is definitely different between the 2 positions as well. How much if any that contributes I don't know.
This was just a load I picked, not worked up. Shot decent about 1" for 5. I was switching between this test, a 6.5PRC, & a 16" 308 AR letting them cool. It was 96 degrees. 50 rounds each so I was a bit fatigued by the end.

Left the Garmin setup at prone so it picked up all 15 prone + 4 from the bag. SD pretty good for Virgin brass & Lever.

 

[Veracity]

I shot for shift today.

3 rounds prone - 3 rounds bagged tight to magwell x 5 cycles
On the last round prone I shot 1 at small dot upper left, same for bagged, but I dialed U.3 & L.2mil.

There is definite shift, but I certainly had a bit of wobble of the bag. Grip is definitely different between the 2 positions as well. How much if any that contributes I don't know.
This was just a load I picked, not worked up. Shot decent about 1" for 5. I was switching between this test, a 6.5PRC, & a 16" 308 AR letting them cool. It was 96 degrees. 50 rounds each so I was a bit fatigued by the end.

Left the Garmin setup at prone so it picked up all 15 prone + 4 from the bag. SD pretty good for Virgin brass & Lever.

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Appreciate the data. Nice work building in the reps of a drill while also doing some testing and load dev.

As far as stability. Kneeling or sitting? If kneeling, double knee down or strong side knee up?

Also, for anyone interested I added the link to my targets. Broken down into .1 mil grids (at 100y) with measurement reference for group measuring apps.

 

[flogxal]

I shot for shift today.

3 rounds prone - 3 rounds bagged tight to magwell x 5 cycles
On the last round prone I shot 1 at small dot upper left, same for bagged, but I dialed U.3 & L.2mil.

There is definite shift, but I certainly had a bit of wobble of the bag. Grip is definitely different between the 2 positions as well. How much if any that contributes I don't know.
This was just a load I picked, not worked up. Shot decent about 1" for 5. I was switching between this test, a 6.5PRC, & a 16" 308 AR letting them cool. It was 96 degrees. 50 rounds each so I was a bit fatigued by the end.

Left the Garmin setup at prone so it picked up all 15 prone + 4 from the bag. SD pretty good for Virgin brass & Lever.

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I'd be curious about the loads generated if you moved the sandbag leftward and put the handguard into the L shaped part of the barricade. Bag below, barricade upright stabilizing from Left. Not snugged up to the magwell for depth on the port. More adjacent support, standing position, using that L shape in the barricade. The further out along the handguard's length, the more likely you get diversion. If it's going to flex.

 

[357Max]

I'd be curious about the loads generated if you moved the sandbag leftward and put the handguard into the L shaped part of the barricade. Bag below, barricade upright stabilizing from Left. Not snugged up to the magwell for depth on the port. More adjacent support, standing position, using that L shape in the barricade. The further out along the handguard's length, the more likely you get diversion. If it's going to flex.

Thats not how I normally place the bag. Typically kI’d place it long side under rail with the crease up, that is a little more stable. For this test I wanted to see how well the VLTOR monorail resisted shift.
Maybe next time I’ll shoot it normal and see if shift improves any.
On something like a cattle gate the gun is up to the madwell as I tested though.