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Crazy poi change today

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Bluecup

Bluecup

Member
Sep 2, 2018
258
6
New York, United States
Hello AGN,

I live in the North East and had a great afternoon of paper punching, I get full sun from where I shoot starting at about noon. It was actually hot for a little while with no wind and I had my gun zeroed in perfectly. I went inside for an hour or so and when I came back there was a big temperature change and my poi was way off. I have a Hawke sidewinder 4-16x50 and at 26 yards I had to go down 16 clicks about 3/4" and right 10 clicks or about 1/2". Is this normal to have that big of a change? I know a little is normal but this seems to be a lot.

Thank you,

Jim
 
Doesn’t seem normal to me, unless there was also an increase in wind.

tsmith makes a good point, I’m going to shoot my rig, then let it sit in the sun an hour or so and see if the POI changes. I believe heat would just increase the pressure in the air tube. The POI should remain the same. 26 yards is really a short range for such poi changes unless it’s really windy.
 
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One could write a book about the things I don't know when it comes to air rifles. I have several premium air rifles, but I can't honestly say I have noticed this type POI change with temperature, but I can't say I've checked it the same day during such a change. But, based on my experience with cartridge and air rifles, I offer this speculation. If the barrel is not free floated, the stress from whatever supports it can change with temperature. The really different factor with some air rifles (as opposed to cartridge rifles) is the complex and numerous parts that form the "barrel". In a single rifle you may have the barrel itself, a shroud, an air stripper, a moderator adapter, and a moderator. These pieces attach different ways and under varying tension, all of which are subject to change with temperature. The only air rifle I have that seems immune from POI changes is a Steyr, and it has nothing out front but a bare barrel. I know, a sample population of one, statistically insignificant, but maybe something to consider. 
 
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The gun it happened to today was a Nova Liberty, I have had a similar experience with my Air Arms S410 both guns had a Hawke Sidewinder on top and are 22 caliber. There was no change in the wind L.Leon. The Liberty is regulated so I do not believe a pressure increase from the heat would be relevant here. We should think about the barrel and the fact that it would expand and contract causing the pellets to be tighter or looser in the bore.
 
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Bluecup,

It can definitely depend on the make, model, and poweplant.

I use a Benjamin Marauder for WFTF Field Target competition. I noticed a POI shift when the temperature changed. I solved this by removing the shroud, which I discovered was the culprit.

Some lower end scopes (some high end ones as well) also have minor temperature issues as well.

Spring guns, even high end tuned ones for Field Target competition have temperature shifts. Ask some of the top US shooters, and they have different range cards made up for different temperatures, that's how variable they can be.



Tom Holland 

Field Target Tech 
 
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Temperature POI shift can be related to but necessarily caused by just one of these instances. Tom already touched on scopes and a barrel band as issues, and are typically the issue. So most airguns are made of dissimilar materiel that move differently with temperature.So when a steel airtube heats up at a dissimilar rate to the aluminum(on most guns) breech this can cause opposing stresses and change your poi. Also internals being different thicknesses and materiel can expand or contract enough to cause fps changes, affecting your poi. While I'm not familiar with the Nova platform I couldn't point to any particular issue so it's up to you chase it down, or shoot in consistent temps.
 
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I’ve heard that Thomas rifles are known for being resistant to temperature changes, and recent ones are even better than before, but I don’t have mine yet, so I can’t test it now.
Click to expand...

I would guess that is true. I'm sure it is a better air rifle than my Steyr, but, they have in common a clean barrel without a bunch of potential problems attached. My guess, any POI change based on temperature would be extremely minor, and probably due to velocity changes from the heavier, more dense colder air. 
 
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Jim,

As of now, there are no benchrest interest on Long Island to warrant having benchrest competition, although, I would really like to try it, haven't had a chance due to our wonderful weather.

Also, there are different classes in Field Target to fit anyone and everyone. Hunter class would be your best bet, you can shoot either a spring gun, or a PCP. There was a rule change a few years back, that allows you to shoot on ANY height seat. You can use basically whatever you want. Even with whatever physical limitations that you have, we will NEVER turn you away from a shoot, even if you don't have the right equipment. If we know you are going to attend, we can bring setups and rigs for you. Believe me, if you really want to shoot a Field Target match, we'll figure out how.

Tom Holland 
 
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