POI left at greater distance

[JohnnyPDX]

Hi,

Dumb question time, hooray!

I'm shooting very well at 13 yards smacking flies pretty consistently and happy with that.

Yesterday I took a few shots at 22 yards and was getting a POI LEFT by .25" +. What the heck?

I shoot off a bi-pod from a very stable bench at paper and flies. Yesterday I laid down on the ground and shot getting the POI left results.

When I look at Chairgun my POI, at five carefully measured distances, suggest I'm shooting at 700fps with an Altaros regulated TalonSS .177. I don't have a chrony.

Pretty sure Im not canting the gun and the scope was CAREFULLY plumb aligned to the gun.

[CraigH]

Possibilities, depending on gun and velocities and pellet;

Barrel and scope not aligned in horizontal plane

Pellet spiraling

[JohnnyPDX]

OK. I took the tank off and clamped the gun to a counter then totally leveled it using the flat top of the Talon frame. Hung a plumb line then carefully got the vert. crosshair plumb. It took forever!

Pretty sure it's on. Human error in shooting seems likely and I don't know squat about spiralling.

Thank You!!!

[Mole2017]

Just going from bench to prone could do it. I got the same thing from shooting off a bag versus a shooting stick. The changes in support and posture can ever so slightly change the forces applied to the gun through the points of contact resulting in shifts in POI. People have even noted changes due to coats and gloves.

[Roadworthy]

Have you tried adding a scope level?  It's possible to deviate a bit from level without realizing it.

[Chris USA]

Johnny,

Bench at 13?, 20, 30, 40 and 50 and +? and let us know the results. Scope to barrel alignment will show itself if that is an issue. Keep (everything) the same with all test(s) and refill if needed.

As for session to session,...... I shoot at my sight in range (every time) and adjust the scope a few clicks if needed. At least 5 shots. Gun, scope, fill, ambient temp., humidity, etc. can all cause small variations. A simple change in rest or hold can (easily) do the same. 

[nced]

Hi,

Dumb question time, hooray!

I'm shooting very well at 13 yards smacking flies pretty consistently and happy with that.

Yesterday I took a few shots at 22 yards and was getting a POI LEFT by .25" +. What the heck?

I shoot off a bi-pod from a very stable bench at paper and flies. Yesterday I laid down on the ground and shot getting the POI left results.

When I look at Chairgun my POI, at five carefully measured distances, suggest I'm shooting at 700fps with an Altaros regulated TalonSS .177. I don't have a chrony.

Pretty sure Im not canting the gun and the scope was CAREFULLY plumb aligned to the gun.

Perhaps............
1. The gun is being held canted


2. My guess is that scope reticle isn't aligned to vertical/horizontal (my issue when I had the same problem)

* To align my reticle I put a "known good level" on the flat of my barrel pivot block and center the bubble.......

* Then I loosen the scope rings and while the level bubble is centered I rotate the scope till it aligns perfectly with a hanging line 18 yards away........

* Then the scope mount strap screws are snugged down in an "X" pattern about 5 in/lbs at a time. After torquing re-check that the level bubble is still centered and vertical crosshair is still perfectly aligned with the hanging string.

3. Dovetail grooves are machined "crooked"

4. Barrel isn't aligned with receiver.

[Back_Roads]

 Going from close range to longer range it may seem spot on up close but typically after a 10 yard rough zero, I take it out to 30, and there may be a few clicks needed to finalize the longer zero, repete at 50- 100 if you shoot that far.

[JohnnyPDX]

You guys are awesome. I thinks it's operator error as it typically is with me at least. I was meticulous with alignment but that doesn't mean it's right.

I will add a scope level today courtesy of Home Depot and a string level. I'm a TIG welder and fabricator so I'm used to measuring stuff pretty good. When tightening down the scope, after a long session getting the gun and scope level together, the scope DEFINITELY moves (rotates) so you have to compensate and do it slowly.

I'll add a level and shoot prone off the bi-pod to see if:

1)  shoot a few with what my eye THINKS is level and see if I get the same results

2) what I THINK is level is actually level

3) shoot a few with what the level says

* regulated the gun is ridiculously consistent and favors lower fill pressures. I think because I set the reg at 100bar.

[ac12]

Stable platform of your bench is very different than the bare ground.
Also as was mentioned, your body position changes.
It is all about consistency.

[triggertreat]

You have done the right thing by using a level and a plumb bob as suggested by previous, knowledgeable members.  I redo this procedure if I ever remove my scope from the rings, otherwise it's not needed again in my experience.  I don't use any levels beyond that procedure, but it doesn't hurt to reference one mounted on the scope, or with the scopes that have a built-in level.  I do shoot long range on occasion beyond my normal range of 50 yards or less, but I have developed a sense as to how level my guns are before firing.  This came with practice for me as I was too overly concerned with my airgun beginnings about being level.  These days I am not.

I recently took out two small squirrels on the ground at 75 yards out with one shot each, so I do believe there was no cant going on.  In a hunting situation you may not have time to reference a scope level.