Impacting low in warmer weather?

[arrow]

I am shooting 105 berger vld hunting bullets out of my .243 winchester with a 24" barrel. My load is 40.5 H4350 .090" jump. I have been shooting this rifle for about 8 months now and up until yesterday things were going great. I have now come to a road block that I cant figure out.

I am using shooter app and it has always been right on for drops out to about 550 yards. This is as far as I can shoot in the area. I plug in 2900 fps which is what the chrono says and has worked perfectly up until now. I am using a kestral 4500 to gather conditions which yesterday where:

29.90 Absolute Pressure
65*F
53% RH

I checked zero at 100 yards. Plugged all this into shooter and it spit out 10.2 MOA. I shot one 5 shot group at 545 yards and to my surprise was about a 2.5" group 5" low. Almost a full MOA low at only 545 yards. I went back through checked my data book and saw this should be about right. I dont have my data book with my right now but I will give some examples on this thread when I get it. I am shooting at sea level so that hasn't changed. RH wont effect anything at 545 yards. I have been doing most of my shooting around 30-40*F. Now it warms and if anything my groups should be higher but this one was low. All components have been from the same lot.

Just to double check my sanity, make sure I did this right. When I confirmed my 100 yard zero I was .75 moa high. So my turret was brought down to - .75 moa. I didnt float my turret before shooting the 545 yard group. I set my turret to 9.5 moa because I started off .75 negative. I did this right, correct?

Playing around with the software I found it would take somewhere around 2780 fps to hit 11.2 moa elevation at 545 yards.

Any ideas?

 

[Canadian Bushman]

Man thats weird. I would go back to 100 yds and reconfirm zero and zero turrets. Then i would dial the scope an even increment ( say 10 moa ) and shoot a group. Then check to see if your group actually moved the distance you dialed. And verify that the elevated group is directly above your zeroed group, I.E. not canted. Then after that dial back to zero and comfirm with another group. It burns some bullets but its good proof of how well you and your optics are working together.

Id like to add that i collect dope on all my rounds, and shoot from my proven data. I love shooter but it cant handle the numerous variables to why a round may hit a minute one way or another.

 

[ColoYooper]

Checkout threads here and at SnipersHide.com about the ladder test. Minor variations in temperature may be producing subtle varitions in velocity, which CAN produce SIGNIFICANT variations in group location (depending on the current direction of the ring of the barrel). By performing the ladder test you MIGHT find a more forgiving load where minor variations in velocity due to temperature/powder charge/bullet weight/case wall thickness/etc will result in virtually no point of impact change.

 

[Broz]

Two questions.

Are you indeed at sea level?

And check you shooter program and see if you have inputted wrong data in the powder temp areas. I would just zero them out for now.

Jeff

 

[arrow]

I am at sea level. I was shooting about 10 minutes from the water. Either way I was inputting 29.90 absolute pressure. Powder temp is set on 0. I have checked and double checked all inputted information. Its just strange to me because I have shot close to this distance in the past and the elevation was right on with shooter. I havent been able to do too much data collection with this rifle yet, but everything I have tried has been right on up until that afternoon. Maybe I will just shrug it off for now and try it again next time as well as other distances and compare them to shooter.

 

[Broz]

Powder temp is set on 0. I have checked and double checked all inputted information.

In your bullet data, go into edit and look and see what you have under "MV variation" It is right above powder temp.

Jeff

 

[arrow]

Velocity variation is set to 0.00 fps/*F.

Just something I though of, the mirage was pretty bad that day compared to what I have been shooting in. I have been shooting in colder weather (for north carolina) but that day was warm and sunny and the mirage was coming off the ground. It had about a 6 mph wind from the 11 o'clock so it wasnt a boil. Could this effect it in any way? Probably not 1 moa at 500 yards could it?

 

[Broz]

Velocity variation is set to 0.00 fps/*F.

Just something I though of, the mirage was pretty bad that day compared to what I have been shooting in. I have been shooting in colder weather (for north carolina) but that day was warm and sunny and the mirage was coming off the ground. It had about a 6 mph wind from the 11 o'clock so it wasnt a boil. Could this effect it in any way? Probably not 1 moa at 500 yards could it?

Yes, if your target image was wavering it can appear to lift the target. That would make you shoot low, or under it.

Jeff

 

[arrow]

Would 5" low at 545 yards (over 1 moa) be possible from mirage? It wasnt boiling either. It was left to right. What do you think?

 

[shortpants]

When you checked your zero was it 1 shot, a group, did you recheck after making the .75moa adjustment? If it was 1 shot or even 1 group and then you adjusted the turret and then went straight to the 500+ yard shot perhaps the zero adjustment was not necessary. Just a thought???

 

[Broz]

My question is was there mirage when you zeroed at 100? I have sure seen mirage mess up a zero more than 1 moa at 100. If you are off 1 moa on your zero you will be off 1 moa every where.

Jeff

 

[arrow]

Thanks for all the help guys, I see what you are saying. I shot a group of 3 right where I was aiming at 100. Shot that group. A little later that day shot a couple more rounds at 100 just to confirm and everything was good. Would it be beneficial to forget about that day for now and try everything again starting fresh next time and see what happens? Jeff do you always confirm zero at the start of a shooting session? Does it ever change on you?

 

[shortpants]

In my experience the biggest factor in an inconsistent zero is inconsistent form. Also a change in position like from bench to prone or bipod vs. backpack. Not saying this is your problem but it goes along with your question about trying it another day. I think that's a good idea. If it happens again then worry about it.

 

[Broz]

Thanks for all the help guys, I see what you are saying. I shot a group of 3 right where I was aiming at 100. Shot that group. A little later that day shot a couple more rounds at 100 just to confirm and everything was good. Would it be beneficial to forget about that day for now and try everything again starting fresh next time and see what happens? Jeff do you always confirm zero at the start of a shooting session? Does it ever change on you?

I periodically check my zero's. But they seldom change. If I have something look like it was wrong I will check it pronto. But it was usually me.

I have seen rifles loose zero, it can almost always be narrowed down to scope or mounts. And more times less expensive rails and rings than less expensive scopes.

You do need to go shoot again. Get a log started, record your load data, rifle, field conditions, angles of shot, dial up used and how low or high the impact was. Then once you have enough actual field data, you can reflect on this data from home to get your drops spot on in your program.

Jeff