scope zero question

[deanothehunter 34]

just a question, does anyone actually check their zero on every outing ?. I recently been out a few times but zero spot on at 30 yrds then today i go out and its slightly adrift not by much but scope has not been knocked or touched in any way, i know some people say just topping up your buddy bottle if you go slightly over....for instance mine is 200 bar but have been told if i went over by 5 to 10 bar it will decrease in power and make the pellets strike lower until the pressure in bottle gets back to or under 200 bar. most buddy bottles wont allow over filling mine included but can maybe go a fair bit over but it has a blow out valve that will stop this after so much pressure, i always top up to 200 bar and stop so its very unlikely it was over pressure that caused zero to be off but in the end i had to reajust the windage and elevation turrets a touch its now perfect again but unless gun gets knocked and quite hard surely the zero should,nt move

[Phantom 631]

I rarely begin a shoot without checking Zero first, but I have done.

 

My turrets are external, finger adjustable and just taking them out of the slip if I don't open it up all the way can turn them a half click or more, although it very rarely does.

 

I've found with my new scope that once its set, its pretty much set for life with a particular pellet. But it does need redoing if I swap pellets.

 

Phantom

[spike25blue 55]

This can be caused by temperature changes which make make your scope mount expand and contract and can cause slight change in zero best thing to do is have your mounts as far apart as possible to try to eliminate this

 

 

Atb rob

[zini 1,939]

Hi Deano,

 

Your rifle zero can change for many reasons both in terms of ballistics and accidental knocking etc.

 

Ballisticially speaking, as Rob has already alluded to temperature has an effect on your rifles performance.

 

Barrel diameter, mounts and other metal parts within the rifle will expand very slightly in warmer weather.

 

A tight fitting pellet in the Winter months (in the barrel) may become looser fitting within the Summer months.

 

This is due to your rifles barrel expanding slightly in its warmer surrounding.

 

This shows massively when using a centre pin rifle where heat is transferred from the combustion of the powder and along the barrel heating it up in turn making it expand slightly.

 

Air rifles obviously don’t do that but the whole heating from the warmer weather / sun also does effect your rifles performance.

 

In the Artillery we always warm our guns (the barrels) to combat the effects of cold gun by firing 3 to 5 rounds to heat the guns up first.

 

I have found this to show better when using a good reliable chronograph and testing the velocity of your own air rifle with the same pellet in the Winter and the Summer months.

 

My r10 changes velocity and I have to keep changing profile data in ChairGun over the year to keep it accurate.

 

It can change sometimes by points of a ft / lbs depending on ambient temperature.

 

We are only talking 100th of an mm here and not huge amounts of change, but just this problem alone will cause a difference in POI.

 

Driving long distances with your rifle in the boot / back of your car in its bag will also have an effect on rifle zero.

 

Road humps are a nightmare on scopes and it doesn’t really matter how slow you go the rifle and you always feels the hump through the suspension.

 

There is also the human factor and the problems of parallax, shooter not shooting so well on one particular day when zeroing and the next day check zeroing and the scope isn’t bang on zero.

 

It could be that the shooter paces their zero range out and one day the paces are large and the next they are smaller paces so the POI will fall high.

 

In summary I try to always check my zero before shooting. The times that I haven’t I have found that I have been out.

 

Si

Edited October 19, 2010 by zini

[pianoman 3,586]

Hi Deano

I found a long time back how I come home from a cold day's shooting, riflescope's been perfect then, after a night or two in a warm room, the zero's shifted off a few clicks I always check zero before a target practice session or hunting. I have a Bushnell Scopechief 4-14X50 scope on my TX200HC .177 and that's a beauty. It moves just a click or so in winter and stays on zero in summer. But other than this, I've never yet found another make of scope that stays rock on zero from one day to next, precisely for the reasons the lads have stated already.

 

ATB

 

Simon