FX impact POI rise

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DBrickashaw

Member
Nov 15, 2017
61
1
AZ, United States
Has anyone experienced a POI increase while shooting in warm weather? My theory is that as the guns temperature increases from being outside in the sun the POI moves up. 

My experience: sighted in a new to me impact 25 last weekend. Shot it today and was dead on for the first mag, then I had to keep holding under. By mag 5 I was holding under 2.5 mils. Target stayed in the exact same spot 30 yards for the whole time.

I live in Phoenix, it is currently 98 degrees outside, vs 74 degrees in my house. Anyone have a better theory to explain the rise in poi?


 
Check and monitor your regulated pressure gauge. 

Mine does the same but it’s due the regulator creep. My Impact is not an X but the last version before FX upgraded to a larger regulator. My first magizine shoots low because the regulator pressure is high and the hammer spring doesn’t hit the valve hard enough to compensate the pressure creep. Once the regulator settles down then it’s pellet on pellet. I’m either going to sent it in for warranty repair or install a Huma regulator. 


 
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Heat will raise the bottle pressure but not as much as some folks perceive, but in a regulated gun it shouldn't matter much if at all. The scope on the other hand may be more susceptible. Checking the reg pressure as you go is at the top of the list but if you're out in the sun, keep the scope shaded and see if it makes a diff. Temp will still go up with possible effects but not as dramatically if not in the sun.

It's not uncommon for FT shooters to have multiple range cards/marks for increased temps.
 
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I also live in the Phoenix area and a regularly shoot in my backyard at a little over 30yds. I don't have an Impact but I do have an FX Royale and Wildcat. Neither gun experiences a shift in POI due to the heat. I have noticed while shooting at a local dairy that my bottle pressure will rise with exposure to the sun but my zero holds true.

Do you have access to a chronograph to see what the velocity is doing? That certainly help diagnose the issue.
 
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Without making any adjustment I took 10 shot after 4 hours of the gun being inside in the air conditioning. This all 10 were 1 mil high vs 2.5 earlier in the day. I checked the regulator periodically throughout the day and no change (that I could tell). But the cylinder pressure did drop 25 bar in the 4 hours between shooting. I am at a loss. I’ve seen my daystate have a 25 bar drop after cooling down, but still confused about the POI fluctuation. 

Thanks for tip JCD, that makes sense. I have a Hawke Airmax 6-24 mounted right now with FX no limit rings. Thinking my next step will be mounting my Aztec and seeing if that changes things. 

Unfortunately I don’t have access to a chronograph. But I’m very curious to see what the readings would be. Maybe I’ll look into picking one up, hate to buy something I wouldn’t use much though. 
 
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