Any Ideas?

[DW5]

(Sorry for the long post) I posted the video of the boar I missed last weekend (hopefully I get another shot tomorrow night) and relayed how how bad my scope was “off.” On the first pig I shot I hit him way to the left of where I was aiming. Since he bang flopped I did not know that however. On the video of the pig I missed (facing the opposite direction) you can actually see the bullet hit to his left and behind him. Okay, my scope is off I’m thinking.

Get back home and head to the range earlier this week. The gun had maybe 15-20 rounds max down the barrel since last cleaning but I cleaned before heading to the range. Below is a pic of my results with zero adjustments made to the scope. Huh? I get to thinking that I was not using the IR  illuminator on the scope since the Equinox’s was so bright and working just fine to illuminate my scope as well. It was sitting about 1-2 feet away from me on a tripod. I also can’t remember if I had to flip the daytime/night time cap open on the scope since the Equinox was lighting it up so well with it’s illuminator.

Thinking this must be my problem I call Sightmark to ask them if this is a common problem. The tech I spoke with said while he can’t rule it out he wouldn’t think either one of those things should be an issue. Said he’d never heard of something like that being a problem. Only thing he could think to contribute it too was the cold front that blew in. I don’t “buck fever” on pigs and would admit if I thought I was just pulling my shot. I’ve shot a lot of game out of that particular stand and am very confident in my brace/shot, especially right at the feeder location.

Anyone ever had a sudden change in temps, say 20-25 degrees in about 2 hours effect a shot like this?

[Chris338378]

Where were you aiming for the shots that hit the small diamonds on the right?  I don't see where having the IR Illuminator on or off should have any affect on the scope's zero unless you couldn't see the target and were aiming somewhere other than where you intended to aim.  A 20-25 degree temperature change in two hours is a HUGE change and could absolutely be the cause of the shift in the point of impact.  That's basically like throwing the rifle into an oven and baking it, things will expand or contract with that great of a temperature change that fast.  A trick some people, including military snipers is if they want to reach out further with their shots they'll lay their ammo out in the sun to heat it up which causes the velocity to increase.  This was done by the Canadian sniper who has the record for the longest shot taken. 

[DW5]

I was aiming at the diamond.  Reason I wondered about the IR illuminator, and sorry I should’ve mentioned this to begin with, wrote that post pretty hastily, is I am aiming this scope using a digital projection onto an LCD screen with this particular optic. Never used anything like this before. I did not know if the position of the illuminator would affect how and images projected on the screen.

Man, I’ve never had a temp drop effect a shot before. Learn something new every day. I’ve only ever thought about  if the rifle has had reason to heat up. I suppose I’ve thought about cold on the few times I’ve been hunting and it has been truly cold out, but never if it was 40 degrees. 

Thank you for the response sir!

[DW5]

On the bottom right diamond I pulled one of the shots to the left about an inch and knew I did it as soon as I pulled the trigger. The other shot out there is just b/c I was aiming there. While this scope can be used in the daytime, that is absolutely not its primary purpose. Once you make a hit on a target, your bullet hole is gong to be by far the easiest thing to aim at sight wise.

[terminator]

I cant see how those temp differences would cause that much shift. I have seen changes from summer to winter with heat sensitive powders like RL22 and IMR 7828 etc but never POI changes that much. Maybe something to do with the night vision scope and temp changes?

[DW5]

I cant see how those temp differences would cause that much shift. I have seen changes from summer to winter with heat sensitive powders like RL22 and IMR 7828 etc but never POI changes that much. Maybe something to do with the night vision scope and temp changes?

That’s what I’m hoping at this point

[224KING]

Bigfoot did it

[DW5]

Bigfoot did it

I’ll get him one of these nights too if I get a shot.

[DW5]

Pigs decided not to show up last night Oh well, they will surely be back.

[zonie]

If you would please,  could you give makes and model numbers of all equipment you were using,  brand and model of scope,   IR Illuminator etc.  I would like to read up in detail on the subject.   If you were using a normal scope I doubt it would be a huge difference on point of bullet impact with various outside temps,  NOT to say there could be NO  differences it's more a matter of how much difference.  What was the distance you were shooting at the hog and at the target ?  I've hunted with one particular rifle where temp swing during that years hunting season were from minus 20 F below zero  to around 115 degrees F above zero and in all cases very little point of impact shift when double checking the rifles zero @ 100 yards such as a pre-hunt check.   It's a very consistent rifle / scope combo that I really haven't changed loads or scope setting in years basically if it ain't broke don't fix it  with this rifle,  sadly I can't say that about all rifles and have to tweek them until  accuracy and point of impact is consistent.  Nothing  more irritating to me at least with rifles is inconsistency,  accuracy may not be the best,  but if the rifle is a 2 " shooter it's a 2 " shooter as long as all the bugs worked out,  and load work-up has been completed correctly.    When you  are talking lcd screens and digital stuff all bets are off  on my comments  I just don't have the experience with them to make any credible statement.   I would like to get the full story and set-up to.       

[DW5]

Sure. (let me know if I leave anything out and I'll fill in) Rifle is S2 Vanguard 20" 308win. Load is factory loaded Nosler Trophy Grade 150grn Accubonds. Nightforce picatinny rail, Vortex High rings. Scope is a Sightmark Photon XT (recently discontinued model in favor of the new RT model) 4.6x42. The IR illuminator  on this scope is whatever comes standard on the Photon XT. More IR illumination was added to the mix from the Bushnell Equinox Z 6x50. IR illuminator being whatever comes standard on that Equinox.

The shots at the pigs were right at 100 yards, give or take a 2 or 3 yards. Pretty windy that night, but I'd think it would take some WIND to effect a 150grn bullet from a 308 like that at 100 yards. Temp started out somewhere I believe in the mid 70s. A coldfront blew in a few hours earlier than forcasted and it had dropped to 45-50F at time of the shot I think. I am completely without cell service where I hunt and didnt make it back to the truck to see the temp for a bit after all the shots had been taken so I am giving what I believe to be an accurate guess on the exact temp.

[224KING]

I'm just wondering about you having a really bad case of parallax the way everything was set up?

[DW5]

That’s what my basic first thought was after learning the scope was still dead on. That the other IR from the Equinox was doing it somehow. The Sightmark tech was very skeptical of that but said he couldn’t absolutely rule it out. I need to bite the bullet one night and drive up to one of the couple of places I could test the theory at night. I’ve got a place or two I could do it it’s just gonna be a haul for me. But I should definitely do it.

Of course Bigfoot is still a real possibility too....

[Chris338378]

It maybe a case of thermal drift from the big temperature change.  Eo-Tech put out a bulletin a year or two ago that said they had problems with their optics with thermal drift.  I can't say for sure this is the cause but it's worth considering.

[zonie]

Yea I think I'd go out again and try to duplicate the scenario and see if it happens again.