24 hour POI Shift – Consistent – Walther LGU – any ideas?

Forums Springers, Pumpers, C02, & Replicas 24 hour POI Shift – Consistent – Walther LGU – any ideas?

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    bdzjlz
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    In all of my now decades of airgun shooting, I have not ever experienced the issue I have currently with one of my airguns.

    A few weeks ago, I posted a comprehensive review of my recently acquired.22  Walther LGU Varmint.  While this rifle is extremely accurate as indicated, about every day that I take it out of the vault, it will print almost exactly 2" lower than when I put it away the day before.

    I am using Sports Optics fully adjustable mounts/rings with the stop pin installed.  I use the ring adjustment to get it close, and then fine tune the Vortex Diamondback 6-24×50 FFP from there.  It does not appear to have any horizontal movement, only vertical.  

    Within five to ten minutes, I will adjust it and have it shooting dead center, and then it will hold that way for many shots the rest of the day until I put it away.  24 hours later, it seems to be back to approximately the same spot, about 2" low.

    I am storing it in a humidity controlled vault at +/- 65 degrees.  It has a synthetic stock, though none of my other 7 rifles have ever indicated this trait.

    Any thoughts?

    Thanks, and Happy New Year!

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    Springrrrr
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    What is the temperature of the room or area you are shooting in.  The differential between your storage area and your shooting area could be significant enough to cause the metal of the barrel and receiver to respond more than the stock and make a fractional move that translates to the two inch drop.

    Try keeping the gun in the shooting area either overnight or for a few hours and see if the POI stays the same.

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    TiredRooster
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    Hmm. Thats one of those little gremlins that get in there and do their dirty work over night.

    Seriously, those Vortex scopes are awesome and tough as nails. I have two mounted on air rifles that I own. But….just to rule out the optics being the problem. Why not take that scope off. Put another scope from another gun on it and sight that scope in perfectly and put it up. Try it a day later and see. If you have the 2" drop then, you just eliminated the optics and narrowed the problem down to the rifle. If it's the scope……..you have that VIP Forever Warranty with Vortex. They will give you a new one.

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    OkAirgunner
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    I had a BSA Platinum on a TX200 and when it would heat up it would change the POI. For some time I figured it was the gun. Then I figured out it was the scope. I ordered a Hawke 10-50, shot it one weekend and the next weekend it started doing things that I could not figure out what was going on. I finally did a box test and figured out it was the brand new scope. If I were you I would do the box test or try a new scope. 

     

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    bandg
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    Some chronograph readings would be helpful.  Could be velocity or could be a mechanical change but I'd think it is temperature related.  Have never seen this with my LGU or LGV.

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    pmg
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    I’m no springer expert by any means and I can attest to the quality of the OP’s shooting area, I’d give my left nut to have that in my basement and I’d expect most others here would too. I’ve been in the vault, or should I say airgun heaven, and maybe the Walther doesn’t like its place in the line up with its synthetic stock next to all of that gorgeous Air Arms wood. With that being said jokingly, here’s a long shot, have you tried storing it horizontally  instead of your usual vertically in the rack? Being a rank novice, can the lube creep enough to cause this? Good luck, and I hope you enjoy the holidays 

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    Franklink
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    Sounds like a springer to me. 

    I tried, really TRIED, to enjoy field target with springers. Various high end springers, and couldn't get rid of the exact problem you describe. 

    Some of it is biological, and I'm not meaning that as an insult. Some if it is mechanical. And some of it goes back to the "springers have soul" comment you always hear. Sometimes a springers soul is just pissed off and it won't perform on a specific day or in certain conditions etc. 

    The best I could do for a consistent poi was an HW50s. And I think it's an outlier (unicorn perhaps?), nearly all the rest were unreliable frustration makers. 

    Having said all that, it sounds like I hate springers. I actually quite enjoy them. I just gotta remind myself to lower my expectations when shooting them. That ease of use, aint gotta worry about shot counts and compressed air etc comes at a price. 

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    bandg
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    Doesn't sound like the Walther springers I'm familiar with.  They have been by far the most consistent of the rifles I own.  The odd part of this is the "consistent" notation for the change.  Sure seems like something mechanical/environmental happening during storage but 2" change seems like a lot.  How far are you shooting to see that change?  Have you checked for velocity variation?

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    bdzjlz
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    18 yards – I have spent a lot of time with the chronograph and this rifle so I have a lot of data to compare to.  Will test again in the next day or two assuming I see the same shift.

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    bandg
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    2" seems like a lot of change for 18 yards.  I would wonder about first shot velocity after taking it out of your vault since you note that it stabilizes to normal accuracy after noting the first shots low of prior POI.  Is it possibly that low in velocity for the first shot or two and then rises to prior POI after a few shots?  Logically though that doesn't make much sense either because you note it is stable after re-zero and would seem to continue to move if re-zero was done quickly.  Still sounds mechanical.  I assume no pressure on barrel during storage?  Possibly scope or mount issue?  No interference between cocking arm and barrel?  Certainly odd and not at all in character for my personal Walther rifles which are really my most consistent from day to day.   Odd.

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    bdzjlz
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    Today's update: 9:05 am

    Left rifle out of the vault last evening – and on shooting bench in exactly the same environmental conditions as where I left after testing it yesterday afternoon about 4:00 p.m.  At that time, the rifle was shooting nearly hole-in-hole at center of target.

    This morning, it shot 3/4" low, and shot a 10 shot +/- 3/8" group without moving, with a chrono (from the first shot) consistency of 658 to 666 over the 10 shots.  Used the Sports Optics adjustable rings to move the scope to center POI as opposed to adjusting the scope reticle adjustments themselves.  Shot 31 shots in total.  The last 10 shot group is as shown below.

    Other interesting factors.  

    Out-of-the-Box Chrono numbers approximately four weeks ago were (in the exact same conditions, exact same range, nearly exact humidity and temperature): Hi = 693 / Lo = 676 / Avg = 681 ES = 17 / SD = 4 over 20 shots…..

    This morning's comparison (31 shots): Hi = 666 / Lo = 649 / AVG = 660 / ES = 17 / SD = 3

    Note the approximately 30 fps loss in velocity.  The pellet the rifle likes the best is the H&N FTT(5.53mm diameter) in 14.66 grains.  I did finish one tin and start another earlier this week, and am shooting straight out of the tin, no hand weighing or head size sorting.  However, the POI shift issues have consistently occurred, though this morning, not as drastic.  And again, once it is positioned, it will not shift across even maybe an hour or more of shooting hundreds or more of pellets.  It is just after having set for several hours.

    Here is a photo of the last 10 shot 18 yard group.

     

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    bandg
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    Confusing and probably very irritating but interesting as well.  The loss of velocity is notable.  Could it be the main spring "settling" while stored with decreasing velocity causing the drop in POI?  Possibly a spring that wasn't correctly heat treated?   It doesn't seem that seal damage would cause the issue to occur in steps as you have noted but I'm not sure that the seal couldn't possibly be warming as shot (maybe sealing better) and then firming up when it cools, sealing worse until warmed again.  Others have noted changes with their scope when temperature changes but you noted it was in a stable temperature environment.  Certainly perplexing.  Hope you get it resolved.

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    Springrrrr
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    The LGU is a very easy gun to take apart and inspect.  Look for excess grease (tar) and maybe a bad seal.  A broken spring would most likely show itself as a worse condition than you have.

    I know this is sacrilegious, but you do not need a spring compressor.  Put the rear of the receiver on the workbench and push down on the barrel.  The two pins should come out and that gives access to the internals.  Don't forget to push the bear trap lever down to get the piston sleeve out.

    This can be done if all the other suggestions fail to show results.

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    Windmill01
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    Really only a newbie at gremlin diagnosing but I had two rifles that did what you are experiencing. The first wasn’t a springer but a gas ram. I replaced the seal and ram in that rifle and the problem went away. In hindsight it was very unlikely that it was the ram so I reckon it was the seal.

    The second rifle was a Hw30. The poi shift was similar to yours and on the advice of a member here I stripped it down cleaned it and put it back together using molly. I didn’t replace the seal as I couldn’t obtain one. The poi shift was reduced considerably so that in the morning was an inch high and I then in the late afternoon was approximately an inch low. I stopped chasing the poi shift with the scope and was confident i knew where the pellet would hit at 25 metres using hold over and hold under.

    It was coming into summer here and the temperature changing could have had an impact on the mechanics like others have suggested but I was inclined to blame the seal. But now I’ll never know as I got rid of it.

    Hope you can work it out as It can be and is very frustrating.

    Gary

    • This reply was modified 1 month ago by Windmill01.
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    gonzav71
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    Your adjustable rings are moving. I had the same problem. I solved it by getting a fixed one piece mount – RWS lock mount.

    • This reply was modified 1 month ago by gonzav71.
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    wahoowad
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    Remove all doubt was the best airgun advice I ever received. Have you removed all doubt, meaning is everything consistent between sessions? You didn’t mention if your rings were properly torqued. Or your stock. Also curious your hold….sandbag front and rear? 

     

    My thoughts are on the internals…seal. How many shots on this seal/spring? 

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    bdzjlz
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    Thanks for all of the thoughts.  

    And no offense taken but for those that know me on this forum realize that there isn't anyone more obsessively meticulous than I am.  So yes, ever detail is exactly the same every session.  I didn't get a chance to shoot it today.

    I have ordered an RWS droop compensating lock-down one piece 30 mm mount to replace the SportsOptics adjustable mounts as my next step.  This rifle has had both Hawke Airmax and Vortex Diamondback scopes on it now, and I am absolutely certain it is not the scope.  With the synthetic stock, I have a very difficult time believing that it is a stock movement issue.

    Will report back in a few days.  My Diana 56 Target Hunter just came back from Motorhead.  Tomorrow, I am going to review the difference between Out of the Box and after a Motorhead tune with the 56.  Should be fun!

    I am not worried about this at all.  I will find the fix and appreciate everyone's suggestions and input.  After all, if it went perfect, I would run out of reasons to shoot so much!

    Happy New  Year to all….

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    wahoowad
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    Looking forward to your 56TH post. Love mine and been wondering if a tune was worth doing as it is pretty good as is.

    I would not expect a loose stock to provide 2” drop at 18 yards – that is a lot of drop. But not setting it or checking it would seem like an oversight in a methodical troubleshooting approach.

    remove all doubt.

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