Do Your Numbers Ever Change after Sight In?

[TDB]

Hello All,

For all the experienced shooters out there, I have a question. I'll set the stage. You get your sight in numbers for all your animals before the match. Everything is good. You start the match, and once you cycle to your third animal, do your numbers ever change from your initial sight?

For example, I've noticed that although my numbers are good at sight in (say 8:30 am), by the time I cycle to my third animal (say 10:00 and it's warmed up say 5-10 degrees), my initial sight in number is sometimes off for that (and the following) animal. Oftentimes, it's only after 3 or 4 misses that I'm confident my numbers have changed. At that point, I'll make the adjustment. Probably costs me at least a couple hits.

Is this something anyone else experiences? If so, how do you all deal with this?

[Brd_Hntr]

Where I shoot the temperature/pressure and wind can change significantly between the first and third set of animals. Usually there is little to no wind during the sight in and the first set of animals, but by the middle of the match the wind is up. I try to start on the far animals, when my settings are fresh from the sight-in conditions.

[acorneau]

Temperature and humidity changes can change scope settings but usually not much more than 1/4 to 1/2 MOA. Cold barrel sight-in versus a well-warmed barrel could also change things a little bit.

Also sighting in on a bench can be slightly different than your off-hand settings. There was this recent discussion about that same topic:

viewtopic.php?f=7&t=10092&start=0&hilit=scope+bench

[BCloninger]

What rifle? Is it bedded? What scope? Are the action bolts torqued? Is this always on the same range, or is this across multiple ranges with different daylight changes? Many variables can cause POA/POI changes, and a big part of this game is minimizing those changes.

One particularly bad day taught me to always check torque on scope rings and action bolts. Then it was the importance of pillar bedding a rifle, and finally the necessity to check zero before the match.

[Jerry G]

Yes they do and I am sure it is the light.

I have set up a survey instrument on a target and watched it every hour as the sun changes position in the sky. The animal doesn't move but the image you see follows the sun. I have tried this several times and I keep getting the same results. I have done it at 100 meters, 500 meters and 1,000 yards. It happens every time except when it is overcast.

Moral of the story, don't sight in at 6:PM the day before the match and expect your point of impact to be the same at 9:AM the morning of the match.

[TDB]

What rifle? Is it bedded? What scope? Are the action bolts torqued? Is this always on the same range, or is this across multiple ranges with different daylight changes? Many variables can cause POA/POI changes, and a big part of this game is minimizing those changes.

One particularly bad day taught me to always check torque on scope rings and action bolts. Then it was the importance of pillar bedding a rifle, and finally the necessity to check zero before the match.

It's a CZ 455. It is glass and pillar bedded in a Merier Stock. I have a Leupold fixed 30. Yes - the action bolts are torqued to specification. It seems to happen across multiple ranges. Granted it's usually not more that 1/4 or 1/2 off, but that's enough to miss at turkeys or rams.

[BCloninger]

Solid setup! I'd start wondering about light and mirage, especially with a 30x scope, but that makes it a question for a skilled spotter (you know who you are, don't make me name names...)

[Hotrodrockets]

littel article here:
http://thearmsguide.com/5331/long-range ... t-effects/

Light effect in the verticle plane 1/2 inch , 1/2 inch in the horizontal at 100meters. Combine with mirage up to 1 1/2 inch = Me missing big time!
Ever wonder why you can hit those Rams in the morning but not in the heat of the day?

[Jerry G]

Good link hotrod.

[TDB]

littel article here:
http://thearmsguide.com/5331/long-range ... t-effects/

Light effect in the verticle plane 1/2 inch , 1/2 inch in the horizontal at 100meters. Combine with mirage up to 1 1/2 inch = Me missing big time!
Ever wonder why you can hit those Rams in the morning but not in the heat of the day?

Thanks for this! That explains a lot!
So... seems like I'll just need to start a log book for time of day and temperature.

[DavidABQ]

My scope settings certainly changed from my home range to when I shoot at the NRA Whittington Center.

[Jerry G]

I do have one small problem with the posted article. What is the difference between light effect and mirage? I always thought mirage was caused by bending light rays. In any event, light does change the location where you see the image you are shooting at and it is minutes, not just a few clicks. It does happen on a cloudy day as well as a sunny day.

[Hotrodrockets]

Jerry G : great question. And that's the problem. I cant' find anywhere how to quantify the effects of lighting , or lighting change.

[jneihouse]

From a reasonably well traveled and experienced shooter, who is glad he is a much better spotter than shooter cause there is a lot less pressure that way, the answer is no, our zeros never change on our equipment. In our rimfire accumulation we have several Anschutz rifles, both repeaters and single shot models bedded in assorted Pharr RT/S stocks, a McMillian copy of the Anschutz standard rifle stock and a Stiller rimfire action in one of Frank C's early iterations of a Pharr RT/S. All have proven, top quality barrels. All are topped by either Weaver or Leupold fixed power scopes in the 24-25 magnification range. And the ammo for each rifle has been extensively tested in that rifle and we know exactly how it will perform at each of the four distances we shoot. Notice a theme here. Quality actions with proven barrels bedded to stocks made of material that is not affected by heat or humidity and fixed power scopes that are of a known and respected quality. All that firing ammunition that has made the cut. Eliminate the equipment variable, or at least minimize it, and you are left with only the shooter and the conditions to battle. We literally have packed our guns here in Arkansas and either shipped or flown them to as far east as Jacksonville Florida and as far West as the Great Pacific Northwest and all points in between including Ben Avery in Phoenix AZ, Whittington Center in Raton NM, and the great range at Ridgway PA and the chicken zero that we established here in Fort Smith Arkansas (offhand because we don't shoot the sport off the bench) remains the same no matter what the venue. That said we should also stress that range and lighting conditions of the moment do have an effect on where we perceive the dot in the scope to be in relation to the exact position of the target. In our case we rarely make an adjustment on the scope. I, being the spotter and supposedly knowing all things (yeah right) make an adjustment of where I call the aiming point my shooter will fire at. When conditions are changing moment to moment or are dicey I change calls from animal to animal. My changes are based on where my shooter breaks the shot in relation to the actual impact point of the bullet. We adjust on the fly so to speak. And I do have the luxury of a shooter who can shoot well enough offhand to sight in her rifles that way and is accomplished enough that I know that an errant round is not caused by something the shooter is doing rather than conditions moving the bullet. Silhouette is a tough and at times frustrating sport. If it were easy they would call it golf.

Of course your mileage may vary, all disclaimers apply here etc etc.

John

[Jerry G]

Hotrodrockets, I have been looking at it for a number of years along with some old guy from LA. We compared notes and had the same results from our experiments. with the changing angle of the sun from day to day and hour to hour, I'm thinking it is a little more complicated than my little mind can get a hold of. I do believe the only real 'out' is to get a good zero on the animal you are starting on and hope your spotter is on the ball to let you know where you hit as the light changes during the day.

I set up on my 500 meter target yesterday and the shift of image was as much as 2 minutes over the duration of 10 hours. Most of the shift was in the horizontal plane. vertical shift was about one minute. Keep in mind we are having a lot of smoke in the air here in central MT from all the fires to the west of us. I think that messed with the data a little.