POI change

[XLR]

I was reviewing my log book and over the last three months and 500 rounds, my zero has moved 6.25 MOA right and 1.75 MOA up. Comparison was taken at the same shooting "range". Temp started at 49.5 degrees to last night of 80.5 degrees. Density altitude has moved from around 7100 to 7550 as it gets hotter. Is my POI change due to temperature or mechanical factors? I realize that there could be a plethora of factors that affect this but I was curious on the affects of atmospheric conditions on my zero. I am using a Nightforce NSX with Barret rings. All is still tight. thanks

 

[cavemanmoore]

Re: POI change

I have a similar, albeit more basic, question. Why does our zero change between sessions at the range. For example why do we need the "zero" spot on the Practical Tactical Practice target. I am not talking about a clean bore vs a dirty one. I mean shoot it today, take it out in a month, and shoot it again.

 

[XLR]

Re: POI change

Let me rephrase my quetion. Does atmospheric conditions have a calculatable affect on my zero? For instance, for every 100 ft difference in density altitude with a 30 cal bullet at X velocity, my zero should move "blank". Are there programs out there that will inform me of this so I can theoretically reset my zero without having to fire a shot?

 

[Lowlight]

Re: POI change

What range -- at 100 not really, but at distance yes.

Its too short a distance at 100 yards to influence your zero.

 

[cavemanmoore]

Re: POI change

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">What range -- at 100 not really, but at distance yes.

Its too short a distance at 100 yards to influence your zero. </div></div>

So if I understand you correctly, shoot the 'hide practice target today at 100 yards, put my gun away, take it out in a month and do it again, my zero should not move?

I feel dense asking this, but I really feel I need to know. Thanks, Chris

 

[Lowlight]

Re: POI change

That is correct, in terms of environmental conditions and your zero at 100 yards it should be the same -- However there is big caveat in this, which is, not all rifles, scopes, & shooters are created equal.

The reason we buy these expensive built to take it tactical rifles is specifically so we don't have issues like a change of impact because of the rifle, especially our 100 yard zero. But unfortunately no matter how much we pay for stuff, not all that equipment is up to the task, so we see shifts.

As well, most people don't shoot nearly as well as they think they do, so there can be some consistency differences there among the shooter.

Now, if you zeroed at 28 degrees outside, wearing all kinds of cold weather gear, and then you decided to shoot that same zero at 80 degrees this July, you might see some shifts, but that is more about the combination of factors more than just the weather. If you zeroed it last month at 60 and shot it today at 80, nothing at 100.