POI shift due to Clamp ?

[ladwict]

I had a clamp (like Joe Kool had on below picture of his) installed om my wildcat and I just wonder if this could cause POI issues . To illustrate what I mean I stole a small piece of Joe’s posting about this nice clamp 

The barrels or shrouds just nestle right down into the barrel supports pre-cut upper grove with minimal to no movement. If the barrel is bumped, it just seems to re-center automatically resulting in no POI change. Pending you center the product correctly when it’s mounted. It all works very well.

i have now ordered a slightly different version ,that eliminates the free floating element from the barrel by also clamping the barrel . ( like an 8 shape) anyone who,also,had some POI issues by the style of clamp in the picture ? Could the pre cut upper groove that makes contact with the barrel make the barrel “ stuck ” in a different position when the rifle is moved during transport or so causing my occasional POI shift ( checked barrel grub screw and scope fixation as well ) 

By the way rhe company making these kind of 3D stuff SMWE engineering and its owner are superb ! Really worth checking the website. 

 

[Guest]

I mean to imply no insult in this response and only to help so please don't read into any negative connotation. The Gamo Urban suffers from POI shift as a result of the barrel band so it's common to cut it off and allow the barrel to float. I suspect this is a similar issue here where the temperature expansion between the 3d printed plastic and/or the barrel and/or the air tube are vastly different. For example, as you shoot, the barrel cools, the air cylinder cools, but the barrel band cools at different points and does not cool in the center as quickly as it cools at other points. Add in some heat and sun and you end up with unpredictable expansion. When you refill after shooting the barrel is cool, the air cylinder is now hot, and the barrel band is now an ambient +- thermal influence. You're effectively strapping the barrel to a variable expansion system which ... results in POI shift.

Have you seen the folks who anneal 3d printed things for more rigidity and thermal stability? Perhaps that process could be applied here. https://hackaday.com/2019/12/18/annealing-3d-prints-a-scientific-approach/

All in all, I get the point of the idea, but I think there's a reason the barrels are floated. I've bumped my Concept Lite a few times (and felt stupid after doing it) but never once experienced a POI shift as a result. I'm talking stupid things like using the barrel for leverage as I attach the foster fitting to the fill probe in the air cylinder and noticed I'm dragging the barrel down until it actually contacts the air cylinder.

Again, not being insulting, and please do not infer I am -- but is this now a self-created problem at this point which was solved by the floated barrel? If 3d printing a barrel band resulted in improved POI wouldn't the folks making the air guns make it as it offers a competitive edge?

 

[ladwict]

Your input is very much appreciated lmnop ! Thanks. Like you I think in the same direction but in this case it is not even a bartel band but just a clamp around the airtube hardly touching , just lightly supporting the barrel as you can see from the pic. But what else could it be when the clamp is involved in the cause of the poi shift indeed. I will keep you posted !

 

[Guest]

Thanks ladwict! Very happy to help opine with you; I am sorry I thought you meant the figure 8 clamp setup and misread. I assume it's the same issue though albeit expressed less. I believe if you do a figure 8 style barrel band that binds the air tube to the barrel it will result in a greater POI shift than pictured in your image.

Thank you and all the best!