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Pellet Gun Perplexing Me


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#1 FC

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Posted 10 October 2011 - 02:00 PM

I've got a fairly new Gamo CFX pellet gun, .177 cal. I can't figure this thing out. It is dead on at 33 feet, but at 74 feet it shoots 2 3/8 inches high, and 1 1/4 inches left! What is going on here? I'm using Gamo Raptor gold pellets, which are the most accurate ones I tried. They are lead-free pellets. Wind was negligible.

#2 machinist1

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Posted 10 October 2011 - 05:16 PM

FC
My limited experience with non-lead pellets is this. The non-lead pellets are so much lighter, that they fly at a greater velocity, making them unstable. I tried some of the Crossman non-lead pellets.
Try a heaver pellet.
Bob

#3 gun nutty

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Posted 10 October 2011 - 05:23 PM

That's interesting indeed.

If your scope is dead center over the bore, then it's probably rifling.


If the scope was offset to the right a significant amount, I'd expect the impact point to move farther left after the zero range.

One of my buddies would offset the impact point at 100 yards to the right or left a bit to compensate for what was happening at 250-300 yards (I seem to remember about 3" high off center, and about 1/2" right or left depending on R/L twist).

I need to look and see if I can find anything on this. My recollection is that there is an issue with this, I just don't know that it would be as much as 2" at shorter ranges.

#4 pacrat

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Posted 10 October 2011 - 07:27 PM

I've got a fairly new Gamo CFX pellet gun, .177 cal. I can't figure this thing out. It is dead on at 33 feet, but at 74 feet it shoots 2 3/8 inches high, and 1 1/4 inches left! What is going on here? I'm using Gamo Raptor gold pellets, which are the most accurate ones I tried. They are lead-free pellets. Wind was negligible.



Since gravity starts acting on the projectile as soon as it clears the muzzle. At 33 ft the pellet is still on the [rise] from line of sight. Yeah I know that is not actually what is happening. 2 lines, one is line of sight, other is line of flight, which is curved. At some point farther out, maybe even short of 74 ft. pellet is crossing L.O.S. again on its way down. Shooting left that much is probably sight mis-alignment. No help from gravity there. ;).

#5 gun nutty

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Posted 10 October 2011 - 07:53 PM

I was trying to explain gyroscopic drift:

https://secure.wikim...28Spin_drift.29

The wikipedia article on external ballistics is very nice.


Another thread trying to explain a corkscrew flight path of pellets:

http://www.network54...t flight curve-

#6 gun nutty

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Posted 10 October 2011 - 08:46 PM

Oh, and found this review of your rifle with pellet recommendations:

http://www.pyramydai...icles/cfx-test/

#7 FC

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Posted 11 October 2011 - 05:42 PM

I'll look at those, thank you. I'm using non-lead because I don't want my chickens swallowing lead. I'm also using these to kill the chickens, when necessary. I don't feel like poking brains or slitting chicken throats for obvious reasons.

"I would like to clear up a misconception about the wind's effect on pellet drift. A wind from the right does blow a pellet to the left. BUT, if your rifle barrel has a right-hand twist, it also pushes the pellet lower! If your rifle has a left-hand twist, the pellet climbs, besides moving left. What causes the additional movement is precession: the movement of a spin-stabilized projectile at right angles to the force applied to it. Push the side of a spinning gyroscope and it doesn't just move away from you, it also moves sideways in the direction of spin."

#8 FC

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Posted 11 October 2011 - 07:01 PM

I like this link: http://www.arld1.com/
Look further down for the good stuff. Some of it is tough to follow.

#9 FC

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Posted 16 October 2011 - 07:16 AM

The, "Tune Meister" over at that forum had some interesting comments, "A very-poorly-finished barrel crown can tilt a pellet off-kilter as it leaves the barrel. That can result in an eratic flight path of the pellet.

Wind deflects or pushes flying objects like pellets 'sideways' while they're in-flight. The stronger the wind, the greater the deflection. A steady wind will deflect a pellet at a steady rate, while swirling or gusting winds in-particular can cause some pretty-eratic flight results. What I'm saying is that the wind can cause a pellet's flight to be 'curved', and even a light wind will have an effect.

Poorly-made, deformed, or otherwise-damaged pellets won't fly as-straight as good ones will.

If airgun pellets break the speed of sound they've been known to fly in an eratic fashion. We're talking about speeds that are up around the 1100 fps mark, however. It takes a very-powerful airgun to shoot a pellet that fast."




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