Changing Zero

[rem_kujawa]

We shoot this winter match that is at 100 200 300 400 500,how come everytime I go out there the zero has changed.Im not talking about my 100 yard zero.that is always on.All the other ranges change.

 

[memilanuk]

Temperature, barometric pressure, wind direction, lighting, powder or primer lots,muzzle velocity), shooting position/grip, you name it. Lots of little things that add up.

 

[rem_kujawa]

I never change my load and I free recoil,so the only other thing is weather.Or light.

 

[memilanuk]

Rem,

I didn't mean 'changing load', I meant as in 'changing component lots'... powder burn rates can vary as much as +/- 10% from one lot of the same powder to the next. It's fairly rare with most powders for them to vary that much, but it is possible. Same thing w/ lots of primers, etc. etc. Usually I don't see much difference, but it is something that can sneak up on you.

Not having the parallax adjusted out of the scope tends to throw me for a loop once in a while... I'll have a gun that just drills them into a tight group one trip out, and the next trip, or at the next yard line, I can't seem to find my behind with both hands and a floodlight, as the group opens up and/or my come-ups are a bit off. Usually for me it traces back to not having the parallax adjustment set right - more so for large group size than come-ups, but I've seen a bit of both.

The single biggest gotcha I've had at long range w/ come-ups not matching was temp/pressure. Once I got a Kestrel, and learned how to use it in conjunction with a good ballistics program like Exbal or JBM... most of my 'surprises' went away. I will say, though, that inside of 600yds I rarely had *that* much of an issue... maybe a 1/2 minute off, if that. Where I was seeing variances was at 800/900/1000yds, where I'd be as much as 4 *minutes* off by the time I got back to 1k.

How much 'off' are we talking in your case?