Not maintaining zero

Not maintaining zero

Postby rhogg4696 » Sat Jul 08, 2017 8:18 am

Hi

I have a AirArms S510 Superlite FAC .22 with Hawke Endurance 30 6-24x50 scope. I zero'd the rifle on a calm day 16C. Several weeks later with the gun doing nothing but take up space in the gun cabinet and temperature now a nice 21C the gun was shooting 12 clicks too high (3 MOA).

What can cause a scope to change so much while apparently doing nothing?

Rob.
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Re: Not maintaining zero

Postby gdavison » Sat Jul 08, 2017 8:25 am

if its a new gun, did you clean the barrel ? the grease and crud from manufacturing which is left could affect zero over a temp variation
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Re: Not maintaining zero

Postby TenMetrePeter » Sat Jul 08, 2017 8:41 am

and any grease on the hammer rail too.
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Re: Not maintaining zero

Postby rhogg4696 » Sat Jul 08, 2017 8:59 am

gdavison wrote:if its a new gun, did you clean the barrel ? the grease and crud from manufacturing which is left could affect zero over a temp variation


No I wouldn't say it was new. I have fired just over a 1,000 pellets through it.

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Re: Not maintaining zero

Postby gary martin » Sat Jul 08, 2017 12:53 pm

could be scope shift, or the heat may have caused power climb. scope shift, I set mine at 15 deg C at 5deg c scope under ranges by 2-2.5 yards at 24deg C scope over ranges the same amount. Different scopes react at different temps. power climb on a PCP rifle I have had at higher temps. In competition we have to chrono every comp. if you have access to a chrono take some readings. I know if you never had a baseline reading you have little to go on, but if it is close to the limit which I have had in summer, better turn it down.
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Re: Not maintaining zero

Postby rhogg4696 » Sat Jul 08, 2017 2:55 pm

I have chrono'd it and the speed is the same ie. between 920fps and 935fps, as it was when I tested it last so no change.

I have the gun adjusted to fire below 935fps as I had heard that if the speed was over 950fps you can get pellet wobble.

I don't know how to work back from POI being 3.5cm high to a speed. With Chairgun all I can say is that the zero would have had to be 60m to hit 3.5cm high at 50m. That doesn't tell us anything.

Temperature today is 20.5C and the gun is still shooting 12 clicks high.
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Re: Not maintaining zero

Postby Archer50 » Sat Jul 08, 2017 3:07 pm

12 clicks is a hell of a lot to be down to environmental factors and by my calculations, it would need an MV increase of around 200 fps to account for it, so you can safely rule that out as the sole problem. Personally I'd have a good look at the scope and the scope mounts, in particular, what happens to the zero if I give the scope a sharp tap, and I'd check the barrel for shroud clipping and straightness. I like AA guns, but the 12.5mm barrels are distinctly flimsy, shrouded or not, and one little knock putting it in or out of the cabinet could easily account for the problem (don't ask me how I know :oops:).

The big question is whether the new zero is constant or not - and it sounds like it is - so the barrel would be my prime suspect.

Alan
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Re: Not maintaining zero

Postby rhogg4696 » Sat Jul 08, 2017 3:20 pm

Archer50 wrote:12 clicks is a hell of a lot to be down to environmental factors and by my calculations, it would need an MV increase of around 200 fps to account for it, so you can safely rule that out as the sole problem. Personally I'd have a good look at the scope and the scope mounts, in particular, what happens to the zero if I give the scope a sharp tap, and I'd check the barrel for shroud clipping and straightness. I like AA guns, but the 12.5mm barrels are distinctly flimsy, shrouded or not, and one little knock putting it in or out of the cabinet could easily account for the problem (don't ask me how I know :oops:).

The big question is whether the new zero is constant or not - and it sounds like it is - so the barrel would be my prime suspect.

Alan


I don't believe I knocked it either putting it away or getting it out of the safe. How can one check the straightness of a barrel other than by removing it and rolling it on a flat surface? It is shooting the same today as it did yesterday so constant at the moment. The scope is fitted using Sports Match mounts.
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Re: Not maintaining zero

Postby Archer50 » Sat Jul 08, 2017 4:20 pm

That's exactly how you do test it, unless you have access to a laser jig. But in reality, very few barrels, AA or not, are truly straight, and there is no way of knowing whether yours was straight in the first place. When I took my S400 apart for a totally different reason, I found that it had a 3mm bend in the barrel. It still has, but there is no noticeable crossover and it is still capable of 12 mm groups at 40 m, when my shooting is up to it. But if I had zeroed before the bend it could have accounted for a 20 cm change of POI at 50 m depending on its axis.

So I suppose what I'm trying to say is that if you can find the problem and fix it, that's great, and it might not have anything to do with the barrel. But if you can't find it, the most important thing is whether the gun is grouping well and consistently and whether the zero is now constant, and fortunately it sounds like it is.

Good luck and good shooting.

Alan
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Re: Not maintaining zero

Postby Blackbaronfish » Sat Jul 08, 2017 7:07 pm

Some things that has cause me vertical changes in the past

Stock bolt loose or too tight
Loose barel band
Faulty scope
Loose scope mounts
Shroud inserts broken.
Sticky hammer rail

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