Zero shift on travel to new location.

[Brown Dog]

Rifle zeroed.

Travel several hundred miles North (by train).

On arrival, check zero. Bullet MPI low: 2 x 1cm clicks ‘up’ required.

Successfully conduct hunting trip using comeup chart –but adding 2 clicks ‘up’ to all elevations.

Return home.

Check zero this afternoon. Rifle back to original zero (ie 2 additional clicks no longer required).

But….(and I know what you’re all thinking)…..both the Northern zero and the home zero were conducted at roughly the same altitude (within 20m) at roughly the same temp (around 8 degrees C).

I can’t explain this! [img]/ubbthreads/images/graemlins/confused.gif[/img]

Any ideas?

[Dave King]

Brown Dog

This should generate a lot of discussion!!

Both Len and I have seen this and I still can't figure out what the cause might be. (It's definately NOT due to rough handling of the rifle). There is something going on and maybe we can understand it better collectively.

[LB]

I don't know about explaing it, but I can attest to the phenomena?

All it has learned(?) me, in <font color="red">XX </font> years, is to always check my zero upon arrival. LB

[Len Backus]

For the last three years when hunting in the west I have been checking my zero by firing at 500 yards. This way I am sure of the POI at the local altitude. By establishing this at 500 rather than at 100 yards, I also am confident I have adjusted properly for altitude and temperature. Potential drop table errors due to changing local conditions would then have to be awfully small if I am on at 500 yards. (My kills have all been under 700 yards)

[Brown Dog]

Len,

The 500m check to reduce errors at other distances is a good idea, however [and for the purposes of theoretical examination, assuming that the rifle has not been roughly mishandled] why, when conditions are apparently (as good as)identical –less a 600 mile move North- should the zero move? I can't explain it to myself!

My confusion is caused by the fact that the zero shift was discovered when fired under broadly identical conditions to those where I zero at home:

roughly the same alt and temp,

same bipod off same surface (grass/mud),

same rear rest,

Using a rifle built like a girder: its action is glued and bolted to the stock chassis and its barrel has almost enough free-float to get your hand around it! (a minor exaggeration!).

Why then, given that everything is apparently the same (within tolerance!) should the zero drop 2cm at 100m when I travel around 600miles North; only to return to zero when I travel S again?

The only major variable is the 600 mile location change.

It makes no sense !! [img]/ubbthreads/images/graemlins/confused.gif[/img]

[Edmac]

I had the same experience when in Scotland this September. POI 2 clicks right. Got back home, checked zero, back to normal. Weird!!
Ed

[Brown Dog]

Season's Greetings to all!

No one got a pet theory for this that they're prepared to expound in public? [img]/ubbthreads/images/graemlins/smile.gif[/img]