Advanced Marksmanship Zero Shift - One Month of Tracking

[calshipbuilder]

Over the past month, I've been tracking the POI of my first groups of the day/session (cold bore + 2 or more rounds). After I shoot my first group, I put in a correction and carry on with my practice / match. So far I've got ~2.5 moa of left shift built up over a month. My vertical varies quite a bit, but whatever adjustment I put in, I end up taking it out sometime later.

Date	Time	Vertical	Horizontal	Location	Notes
10/30/2017	AM	-0.5	-0.25	Rifle's Only
10/30/2017	PM	-1.25	-0.25	Rifle's Only
11/1/2017	AM	1	-0.25	Rifle's Only
11/2/2017	AM	-0.5	0	Rifle's Only
11/3/2017	AM	0.5	0	Rifle's Only
11/18/2017	PM	0.25	-0.25	Santa Clara	Tightened mount cross-bolts
11/24/2017	AM	0.25	-0.5	Pala
11/26/2017	AM	1	-0.5	Pala
11/26/2017	AM	-1	-0.5	Pala
Overall Shift		-0.25	-2.5

Anyone else tracking their Zeros? Does this type of shifting zero look pretty common?

Today, mid-match, my zero shifted 1 moa low - out of nowhere I started missing low at distance then confirmed on paper, is this normal too?

I'm running an atacr 5-25 F1 in a Spuhr on a pinned rail. I'm pretty confident its more FoM related than equipment.

 

[Clearlight]

A good zero is something I’m picky about , one less error to
account for at long range . The four rifles I have with March
scopes show no zero shift whatsoever other than encironmental
shift . To clarify , the 100 target I use for this at local range requires
shooting over a 50 berm that is quite high . Winds are switchy there ,
so you can shoot a quick group in one wind condition , and shoot
another group 5 minutes later and see it print in a different spot around
the X .

No no issues with the Hensoldt or Schmidt either : only problem
child I have is a PST on a 223 trainer that insists on swapping zero
from up to 0.3 Mil left or right , seemingly at random . It’s going back
to be replaced soon , hopefully the local Aus distributor has run out
of Gen 1 units and I’ll get a Gen 2 replacement .

 

[WB300]

Tag for info on this....

Had this same problem 2 years ago. Narrowed it down to the crappy pipe foam/duct tape cheek riser and incorrect NPA. Went away with a stock pack. Either that or my technique just evolved.

 

[kthomas]

Admittedly I've never tracked my zero before, but that seems like a lot of shifting. I almost never have to adjust by more than a tenth of a mil, and usually it is spot on.

WB300 might be on to something. Are all these zeros taken from the same position? Or are some from prone, some from bench, etc? Your position behind the rifle and the pressure you apply will affect your zero.

 

[Hairy Biker]

There is a group bias being formed that looks more like shooting position (head on stock/cheekweld) or trigger control than scope issues.

As kthomas as - what is your standard position? And is your scope set up correctly - when you chose your eyes and relax is the article in the same position when you open them?

 

[steve123]

I think if all of us are honest we gets slight shifts as a common event. I can go for months with the same zero then there it is, a shift. Sometimes it'll go back the next time out and sometimes not. If you think about it there are a lot of factors going on that influence us and the rifle system. For instance when I shoot in soft cinders then go to concrete the zero goes a click high. When I go to an out of town match there is often a rezero needed, like a click here and there.

 

[calshipbuilder]

Thanks all for the insights.

I'm going to test a few variations of my hold - shoulder pocket placement, cheek pressure, grip pressure, to see what that does to my zero, and if I can replicate the vertical shifts that way. I also want to see what a less than perfect parallax setting does to my zero.

 

[Jimgal62]

I have experienced zero shifts due to powder temperature from begining to end of a competition using IMR 4064, ambient temperature effecting powder and rail/ring expansion and barrel fouling.

 

[Rudy Gonsior]

I have experienced zero shifts due to powder temperature from begining to end of a competition using IMR 4064, ambient temperature effecting powder and rail/ring expansion and barrel fouling.

Unless your talking about elevation errors at distance, it's pretty unlikely that your zero is shifting from ambient powder temperature or fouling, especially with 4064. I'm not saying it isn't possible but its rather unlikely give 4064's track record and potentially irrelevant to the situation, its not where I'd start. Where I would start, is what WB300 pointed to. The shifting around of head/check positions, buttstock shifts or changing your NPA from shooting session to session is a common cause of "zero shift". To some degree the quality of the stock or chassis (or rail for gas guns) can have a big effect, particularly when you load the bipods in different ways or surfaces. Also cleaning regiments can cause some rather radical shifts. Finally your parallax and the lighting situation can have an effect, though typically not to a degree of much more than 0.1-0.2ish MILs. When you start compounding all these things together it can be rather confusing and leave a shooter confounded about whats going on.

v/r Rudy

 

[jsthntn247]

Mine does it too. I think its bedding or scope causing the issue. My F class gun professionally pillar bedded with March scope does not do this. It stays center no matter what range or conditions I go to and shoot at. My 6.5x47 changes every damn time I take it out even from day to day sometimes.

 

[Forward543]

I have this issue as well. Generally in the .1 mil area. I think it is from poor positioning. Getting my position exactly the same everytime is tough. I use an athlon btr, bushnel dmr, and burris xtr. I am pretty sure it is my technique, most shooting done prone in the dirt.

 

[CharlieNC]

This is one aspect the dot drill is aimed at helping. Stand up and rebuild position for each shot, that will show you the human influence. Unless your day-to-day zero is worse, then your rifle system is not likely at fault.

 

[DetroitRearView]

NF ATACR 5-25F1 + 7-35 NF Unimount AXMC spot on centerpunch first cold bore shot with one follow up immediately thereafter - same hole or slightly rounded out @ my 100 yard zero 300N 338L

Same deal with my Blaser R8 NXS 2.5-10 MILr 300 win

For me it was really getting my npa and follow through managed - lots of dry firing, “killing” all of my horses, deer and critters around my place XXXX times

Did test scope tracking?

 

[NWnewguy]

Jeff Cooper once wrote about taking a particular hunting rifle to the range every time he went and putting up the same target at the same range. He would shoot one round and then carry on with whatever he had come there to work on, but only the one shot out of the rifle in question. Different weather, temperature etc...but after a dozen trips or more to the range, you can tell what you need to about that rifle and how well it shoots to the same point of aim. I always thought I wanted to do this, but haven't gotten around to it. Thought it was an interesting experiment anyway.