Any truth to having 2 different zeroes at different shooting clubs?

Melnibonean

Melnibonean

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I read (on another board) that it's possible to have your rifle and optic zeroed at one shooting range, then have to re-zero it at a different one.

So if I zero my rig at let's say EOSC at 100, I may need to re-zero it if I go to Connaught and try to shoot at 100 there.

Any truth to this? If so....what can cause such a thing? I thought a zero was a zero was a zero.
 
The rifle doesn't know where it is. The only thing I can think of that would cause this is extreme cold or heat or extreme differences in elevation. Assuming same loads and bullets used each time. Or maybe I don't know enough about optics and ballistics?
 
Two things i could see that could cause this. Imperfect distances (say one ranges 100m is actually at 95 and the others is at 105) or a change in slope of the range. If one range points uphill while the other points downhill that could theoretically make a difference.

I can't imagine either of these being large enough factors at 100 yards though. At least not with a fast cartridge. I bet it would make a big difference on a 22lr at 100 yards
 
I've also read if you zero you rifle shooting north, there will be slight differences when shooting South, East or West. But the biggest differences you will encounter is temp and elevation changes.
 
100 yards shouldn't make a huge distance. If you're shooting at say 1000 the difference between shooting east opposed to west can cause a decent difference due to the earths rotation (Coriolis effect).
 
Certainly a difference between yards and meters, but even then you're only talking about 0.1 MOA at 100y (91m). A significant change in atmospherics might do it (temp, altitude, humidity, etc.), but I think you'd need to start stretching it out to really see much difference.
 
How many shooters CAN hit their zero from day to day to day... at the SAME rifle range? Easy enough for you to prove how light and ambient can affect POI. Also, how consistent you are in set up and follow through.

Do the cold bore test 5 different days and see what you end up with....

Do zeros shift due to location and weather? Absolutely.

How much? Depends

The further you go, the more everything effects your POI.

I had my 900m zero change over 2MOA at Homestead going from Thurs (cold, overcast) to Sunday (hot and sunny) for a match. I have had shifts over 1 MOA on the same day from morning to afternoon.

Zeros can change a huge amount depending on the elevation of the range... from Chilliwack to Homestead.. be prepared to dial.

Just know what your bullet and YOU see as conditions change.

Jerry
 
Thanks Jerry. I suspected it was more to do with atmospherics and shooter not reading the range properly more than anything else.

I suppose the 100 yard zero referenced on that forum was just to show the phenomena
 
I have noticed a significant difference from my zero set near sea level on the island, and the same zero shot in the hills around Vernon. I attributed it to a change in atmospheric pressure, but based on what everyone is saying here there are many other factors at play.

Thanks,
Cal.
 
The only way your gonna notice a difference between ranges would be if your zero is set at a long distance. If that was the case you wouldn't even need to change ranges just wait for a atmospheric pressure change. With a 100 yard zero there's no way someone is going to pick up on the differences.
 
If some one told me that their zero shifted significantly from different days or locations the first thing I would think is.....

different shooting benches/shooter is in a different position

and or excessive parallax therefore any shift in position will change POI.
 
Since (In your case Melnib) the issue seems apparent at only 100 yards, I wouldn't put any thought into rotation of the earth. At 900 yards, yes, not 100.

I'm thinking the zero for your rifle would not be the same from one day to the next even on the same range.

There's a few reasons that come to mind. First is the effect of fluctuations in temperature. Depending on the cartridge and load data you can get significant variations on ignition rates and muzzle velocity. Changes in muzzle velocity will affect the barrel harmonic and at what point in that harmonic where the bullets actually leaves the barrel.

If the harmonic at one MV has the bullet leave the barrel at a low point in the harmonic, vs the opposite at a different temperature, you will get a change in zero. This is why different bullets hit in different places from the same gun.

You may even have a problem with the rifle itself. If you have the typical wood or plastic stock, temperatures can affect exactly how the action settles into the stock. On that topic, the action screw tension will have an affect. Oil between the action and stock will have an affect.

There's dozens of subtle little things that can play games with your head.

Guys get sick of the whole bedding thing and just glue the darn action into the stock. You may also have seen some guns that use a barrel bedding block. This is another solution where the bedding block is glued into the stock and the barrel is clamped to the block, much like a set of scope rings. with this setup you dismiss the action screws.

There are even studies that show the barrel moving in the action threads from shot to shot. To prevent this from happening there's a special barrel thread that was designed with a two stage V where the tips of the threads have a chamfer that engages from the tip of the thead rather than the side of the V. This ensures that the thread load is distributed over more threads. (All threads do not actually get tight on normal threads, just the first few) This design is intended to ensure the barrel keeps pointing in the same direction relative to the action.

Then you gotta start thinking about the stiffness of your action. (I don't intend to brand bash here) A Rem 700 (for example) is not very stiff as compared to many other actions (Like Savage Model 12 for instance). Any flex that occurs from shot to shot will shuffle the pressures around between the action and stock and can shift your zero.

Ya the shifting zero is an issue that seems to grow in significance in proportion to how accurate your rifle is. A guy with a 2 MOA gun probably would never notice.
 
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Shooting at Milcun over a week, my group of guys would check their 100 yard zero every day before moving on to the longer distances. Everyone's rig was sub 0.5MOA....all experienced but 'non-professional' shooters.
Every day....at the same range..using the same ammunition, the zero would shift by a couple of clicks elevation/windage.....every day....every time.
Not much....but we're talking about multiple variables, each of which can change minimally...but they can all add up to visible change.
 
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