accuracy on multi-pump

[Puppadore]

Hello, I tried out my neighbor's multi-pump gun. His is Crosman 2100, exactly same as mine. But his airgun is doing something weird.

I put my scope on (he shoots just iron sights), and zero-in with 4 pumps. It is accurate. Consistently makes a quarter sized groups. But when I pump 5 times.. it shoots to the left. When I pump 6 times.. it shoots further to the left than before. So more pump is making the shots go left for some reason.

I would understand if more pumps = shooting high, because less pump would mean the pellet is dropping due to less power. But why go left?? there is no wind. My gun, the same exact model does not do this. Would anyone have an idea why this happens and how he can fix it?

Thanks.

 

[Fig]

Maybe bent barrel.

 

[beerthief]

check the crown , i think at low power = less drag of crooked crown ? higher power = more drag ??????
maybe a good cleaning of the barrel ?

 

[SniperX]

Probably uneven expansion of the pressure vessel due to increasing pressure.

 

[AirNGasman]

Varying amounts of pressure in the chamber = varying amounts of pressure on the barrel band = diagonal spread.

Why does his do it and your's doesn't despite the fact they're identical models? Because they're different guns, and EVERY gun has it's own idiosyncrasies, quirks and foibles... just like their shooters. And just like human 'identical twins' aren't.

 

[Puppadore]

If it is due to varying amounts of pressure, what can be done to fix it?

 

[AirNGasman]

The easiest fix is settle on one particular number of pump strokes, sight-in at that charge, and live happily ever after.

Otherwise I'd concentrate my efforts on the barrel-band first. And if the problem isn't found there, expand your search for the problem in that immediate area, moving out. If you can't pinpoint the problem, you'll decide for yourself when to default to plan A...

Or sell.

 

[Puppadore]

The easiest fix is settle on one particular number of pump strokes, sight-in at that charge, and live happily ever after.

Otherwise I'd concentrate my efforts on the barrel-band first. And if the problem isn't found there, expand your search for the problem in that immediate area, moving out. If you can't pinpoint the problem, you'll decide for yourself when to default to plan A...

Or sell.

Thank you. Makes sense!