left a bit

[Philo]

Here's a strange one.
for the last few weeks when I take my first shots they go left by 3 to 4 clicks by the time I have gone through the first mag then I have to rezero back the 3 or 4 clicks and the gun from then on is spot on!!!!! ????

 

[Guest]

A lot of people will disagree with me on this so take it with a pound of salt. I believe even in the airgun world there is such a thing as a "cold bore" shot. In the PB world your first shot warms the barrel and that temperature change shows up at the target. For that reason professional marksmen keep a notebook which contains among other things a log of where the cold bore shot has been landing.

I've noticed this same sort of thing with my springers but not so much with PCPs. I think with the springers the lubricants cold and/or maybe that first shot just shakes out the cob webs? With PCPs I don't have enough experience to try to make any argument about it happening but it seems that you are suggesting something like that.

The only way you can know for sure is to keep that log of "cold bore" shots. You only get one or two every time you hit the bench so... it takes a while to collect the data to support the argument.

 

[scubajeeper]

That is strange, I've never had one of my guns do anything like that. I take them out and they shoot right were they left off. Good luck figuring that one out.

 

[Willie14228]

try this, instead of filling full charge run at about half to 3/4 charge see if that doesn't change your zero, I will bet what is going on is the power curve

 

[fe7565]

It's hard to help without some chrony numbers...and a make/model, etc would help also

 

[Philo]

Interesting, I only ever fill my bobcat to 150 bars. How would the power curve affect Windage ?

 

[fe7565]

Not familiar with the Bobcat, so going out on a limb here. But first: why only a 150 bar fill? I would think that the reg is set at around 140-150bars if .25 or higher caliber. You get to shoot about 5-6 shots and then it falls off the reg. thus your velocity starts to change (most likely drops). A chrony should confirm that.

Let me throw some possibilities out there so at least those can be eliminated:

This is the least likely: There may be a case when the air tank is filled and expands it may affect the barrel band or other tank mounts which may in turn affect POI. This may be only affecting a few shots while the two metals push on each other. When the pressure drops below a certain point the metals stop touching and no POI change anymore. Or something else is causing clipping above a certain air tank pressure/pellet velocity. Again...just a speculation.

Another thing, again just a guess. Certain pellets may change POI with a different velocity behind them. This POI can be a drop and/or in some cases (because less spinning stability) it may curve/spiral which will move your POI left or right. But for this to take place I would think that the velocity change would have to be quite large.

Did you try to fill to the max 220bar or 250bar and see if it starts to behave at the same pressure point every time? Or it only does it for the first few shots regardless of pressure? If it only does it for the first few shots regardless of pressure, then I think there is something with the regulator....but no idea how.

I hope others with more experience chime in...

 

[Willie14228]

If your FPS is changing then it could effect your pellets windage

 

[Smaug]

"scubajeeper"That is strange, I've never had one of my guns do anything like that. I take them out and they shoot right were they left off. Good luck figuring that one out.

It's pretty common. Yet another disadvantage for springers.

Here's a recent discussion with targets as proof: http://www.network54.com/Forum/79537/message/1477777173/Springers

 

[Philo]

Hi there, my bobcat is a first generation gun and those didn't come regged. It's a 12 ft-lb rifle the sweet spot for this particular gun is 150 down to 100 bar which gives me 120 shots at 11.4 ftlb. When I fill to 200 bar the power is back to 10 ft-lb .