If the erector tube in a Z4i scope didn't return to the windage adjuster, would the POI be left or right?

[Alantoo]

As per the title, The cold barrel first shot at the range is regularly with my current hunting ammo to check for zero. It is usually within 1/2” of just under 1" high at 100yards.

Last Wednesday the first shot was just under 2" to the left, I tested it by shooting another 4 rounds of hunting ammo which grouped around the 3/4" high POI. Hmmm.

Subsequent shots of the evening were all as expected, the HPS target ammo has an average POI 1/2" right of POA with the scope set for my hunting rounds.

Trying to analyse the cause of the 2” left aberration, I wondered if the scope could have been knocked in transit and the erector tube jarred off the windage adjuster and the first shot bounced it back.

I couldn't find anything specific for the Z4i and even with cutaways and diagrams I could not figure out with the SFP optical path wether it would cause the POI to shift to the left or right...anybody know?

It is a 10 year old Z4i and it came back from a Swarovski service 4 months ago.

I openly admit 2” left could have been caused by the "jerk on the trigger" and therefore nothing wrong with the scope...but if it was the erector tube springs not returning it fully, which way would the bullet go?

I could then rule that possible cause out if POI would be to the right.

Alan



Previous cold barrel first shots at centre target to show pattern.

 

[Steff]

Did you play around on the windage?
If not then why do you suspect there’s anything wrong with the scope?

It doesn‘t seem to be a brilliantly accurate combo anyway.

Take another cold bore shot.

Another thought. Any oil in the barre or the chamber? Make sure they‘re both bone dry.

 

[Alantoo]

Did you play around on the windage?

No the scope has been untouched since it was zeroed in December 2021.

If not then why do you suspect there’s anything wrong with the scope?

Because it is significantly unusual to have a bullet suddenly impact 2" away from its usual area so I am looking for the reason. I lost a bit of confidence with the scope when it played up last year...hence sending it to Swarovski for a service, so the scope is one of the possible causes I am considering.

I know that the erector tube is pushed from the windage knob side and held against the windage adjustment by return springs. What I don't know is what hand thread the windage turret uses and whether it pushes the erector tube to shift the reticle to the left or right given the upside down optical path.

I was hoping somebody on here knows what left or right effect on the POI a non-returned / sticking Z4i erector tube would have because it may be possible to eliminate it from the possible causes. Otherwise I will have to try and get my head around the complexities, hoping somebody might just have the knowledge to save me the trouble!

It doesn‘t seem to be a brilliantly accurate combo anyway.

The preceding cold bore shots were all within the sub MOA / 0.850" 5 shot group that combination of me, rifle and ammo has produced on average.

I agree it is not a brilliant accurate combo, it is me and a light-ish barrelled hunting rifle...but one shot 2" to the left is still an aberration.

Take another cold bore shot.

I will do on the next range visit as usual, but given that the previous dozen or more cold bore shots were less than 1/2" from expected POI, I am not sure what it will tell me.

Knowing what the Left or Right effect of a sticking erector tube would be at least a 50/50 chance of positive elimination.

Another thought. Any oil in the barre or the chamber? Make sure they‘re both bone dry.

Good thought. I always pull a dry bore snake through the barrel as I am setting up, I seem to be the only one that does...I always ask permission and the RCO is so used to it he makes rude comments about it now

If you look at the "1st shots" bullet holes I marked on the targets, they are all slightly darker than subsequent ones....because of residual oil I presumed....but the point is all the first shots that were within the usual grouping have them, so 2" to the left is still the aberration.

Alan

 

[Andyquadra]

I've got something similar with my 6.5x55
First and only first shot is low right every time then bang on. Its going to get a good clean first

 

[Alantoo]

I've got something similar with my 6.5x55
First and only first shot is low right every time then bang on. Its going to get a good clean firstView attachment 252623

That has been happening with the first shot "every time" for how long? Does it do this when the barrel is due a clean but not otherwise? My groups do tend open up after a couple of hundred shots....it reminds me to chemically clean, but normally there is not such a huge difference between cold barrel first shot and the subsequent ones. Usually the first cold barrel shot is within the sub MOA group.

Alan

 

[Andyquadra]

That has been happening with the first shot "every time" for how long? Does it do this when the barrel is due a clean but not otherwise? My groups do tend open up after a couple of hundred shots....it reminds me to chemically clean, but normally there is not such a huge difference between cold barrel first shot and the subsequent ones. Usually the first cold barrel shot is within the sub MOA group.

Alan

The rifle doesn't see much use, about 100 rounds since new since I've had it. Can't remember when it started, defiantly December last year. The distance the first shot is off does vary, but its always low right, gave its a quick clean Friday and its changed the first shot position, so will be giving it a good clean tomorrow.

 

[Alantoo]

The rifle doesn't see much use, about 100 rounds since new since I've had it.

I have kept a running tally on the targets for that barrel, so 3140 now.

Can't remember when it started, defiantly December last year. The distance the first shot is off does vary, but its always low right, gave its a quick clean Friday and its changed the first shot position, so will be giving it a good clean tomorrow.

If in doubt check all scope and action screws and give it a good clean!

I don't think we have the same issue though.

Alan

 

[Steff]

Clean them after every shooting. Use Ballistol for scrubbing and you will definitely not have a deviating first shot. I know it‘s hard to believe. But just do as I say, as my coach says .