Vertical Stringing

[dale2242]

I have found that most scope mounted break barrel air guns tend to vertical string the shots.
The worst seems to have been a friends Gamo Whisper.
My shooting was done from bench rest, sighting in the scope and shooting for group.
My Crosman Quest does pretty well but will through a shot quiet low at times.
I am hearing the way you hold the gun can make a difference.
Any comments?....dale

[rsterne]

In addition to the way you hold the gun, you may be experiencing a lock-up problem.... If the barrel doesn't return to the same place every time you close it, on those occasions it isn't properly closed the shot will be low.... This is a common problem with inexpensive springs (and the Quest/Phantom are notorious for it) if you mount a scope.... They don't do it with the iron sights because they are mounted on the barrel....

Bob

[Silver Eagle]

On the Quest make sure the barrel pivot screw is tight. You will need to remove the stock to tighten. It should be tight enough that the barrel does not or barely falls under its own weight when the gun is cocked. Tinkerers have been able to add lock screws to this screw to prevent it from loosening.
Inspect the breech seal and replace if needed.
Investigate into replacing the barrel pivot shims which are plastic with brass washers ground down to the right size. Gateway to Airguns forum has a good how to on this upgrade.

[W.R.Buchanan]

I have never experienced this with either my HW35 or my newer R1. Both are brake barrel and both have either a scope or receiver mounted aperture sight. Both have strong barrel indexing features.

The problems indicated above would account for this issue. I mean if the gun shoots stupid with a scope and not with the open sights then the only place to look is at the lockup. Obviously it is not repeating its position everytime.

Randy

[Larry Gibson]

The way you hold the springer can definitely make a difference. If a usual CF rifle bench technique is used ( forend of rifle on front bag and toe of stock in rear bag with off hand supporting the rear bag) vertical stringing is often a result. Also excessive pellet weight variation can cause vertical stringing if the rifle is accurate enough and the range longer than 10M. Of course a bad seal or improper/insufficient lubing of the piston and spring are also causes. However, improper hold while "benchresting" is the main reason. An "artillery hold" with the back of the fore hand on the rest with both elbows firmly supported by the bench is the best position to use when group testing springers. Consistency of that hold shot to shot is necessary as with any accurate shooting.

Larry Gibson

[cbashooter]

Some spring guns can shoot very well held in conventional manner on bench rest bags front and rear. Not all of course but the “artillery hold” is not always the answer. Experimentation in holding on the bags is needed and consistency in the answer. Often you can shot good groups many different holds but the point of impact on the groups varies. Also the temperature on spring guns can change the viscosity of the lube on the spring and as it warms up velocities rise as do shots.

dan T

[W.R.Buchanan]

The temp thing is interesting and I first noticed this a week ago when I shot my first match for the online Silhouette shoot. the gun is stored in a steel box in the garage and it was about 50 F when I started shooting it.

After 30 shots it became a little warmer and it appeared to be shooting closer to where I thought I was holding. This is all speculation since I was shooting off hand. But the gun definitely shot better warm than cold.

Next time I'm definitely warming the gun a little with my heat gun before I shoot.

I have never experienced "Vertical Stringing" on any of my Air Guns, and they all shoot to POA with almost boring regularity and always have. Even different pellet styles make little difference.

Maybe I'm just lucky?

Randy

[HARRYMPOPE]

The point of impact varies with my spring guns with temp also.I live in am area that goes from low 20's and below in the dead of winter to over 100 in the summer.

[Larry Gibson]

The point of impact varies with my spring guns with temp also.I live in am area that goes from low 20's and below in the dead of winter to over 100 in the summer.

Not only does the temp change POI by changing the viscosity of the piston lube but it also changes the air density as does large changes in humidity. The air density is the "powder charge" so to speak with springer air rifles. The denser the air the higher the velocity will be for a given springer.

Larry Gibson

[cbashooter]

To quote Tom Gaylord to back up the air temp isnt much of a factor.

"I actually tested the velocity of a steel spring and gas spring gun at 50 degrees and zero degrees F. The steel spring gun lost 50 f.p.s. at zero degrees. The gas spring lost perhaps 5 f.p.s., which is negligible. A gas spring gun also has some lubrication in the powerplant, but the real culprit for loss of velocity is the decline in pressure inside the gas spring unit"

(not in the column of air in front of the piston!)
the volume correlation factor for air density is about 1 percent for 50 to zero deg.The dynamic viscocity diffrence is only .30 percent as well.Pretty small numbers in most small air cylinders.


dan T

[Larry Gibson]

A 50 fps drop or increase in velocity can have an effect on POI. How much depends on the distance you shoot at. At 10 meters it's probably not much. If shooting field target and you got to slip that pellet through a 1/2" hole at 20 - 35 meters it can mean a whole lot.

Larry Gibson

[W.R.Buchanan]

I agree with Larry on the 50 fps having a measurable effect. The difference between my HW77 and the R1 is about 50 fps with the same pellets.

What this plates out as,, is the HW77 is dead on at 10yds and then again at 40 yds.

The R1 is dead on at 10 yds. and then again at 50 yds.

So there's a 10 yard gain in the trajectory with the extra 50 fps. Not much in cartridge gun land, but a 20% increase in Airgun Land.

Sat after next is my first Small Bore Silhouette shoot of the year. I will be shooting my M2 Springfield on the first relay, and the R1 on the second just to see if I can hit the mark on the 75 and 100 yard targets. I know the gun will knock down the turkeys but the Rams may be a different story.

We'll See.

SHOT Show next week, hope to see some of you guys there.

Randy

[cbashooter]

i've shot my airguns at 100 a bit .Wind is an unreal challenge.Sometimes groups about 2.5" other times over 6" and not worth mentioning.

[dale2242]

Speaking of piston lube, where do I get and what do I use for piston lube for break barrel guns?...dale

[HARRYMPOPE]

I am not a "tuner" but have torn into three lately. I used both green bicycle chain grease and moly grease(in a big tube) from an autoparts store. I just lightly smeared in on the spring careful not to get any in the compression chamber Both lubes have seemed to work fine for me.I know some with more experience have very strong opinions on what and how to do it but I have shot a 1000 or more through each and so far nothing to report bad.

[cbashooter]

The point I made wasn’t that the velocity drop didn’t matter but what did and didn’t cause it.

Kind of like this-

Who was the greatest NFL quarterback ?

Willy Mays

No, he was great baseball player

Boy he sure was good

Thread goes to baseball

[Silver Eagle]

Use Silicone oil in the compression chamber if you are not going to disassemble.
If you fully disassemble the power plant then use a high moly content moly grease (Honda makes a 60% moly grease). Use this on the piston and mainspring being careful not to get any in the compression chamber.
Getting back on topic: Pellet variances can cause inaccuracies including vertical stringing. Try sorting pellets by weight and removing the one's with noticeable skirt damage. Some guns do not like to shoot certain type's or brands of pellets well. Buy a variety and see what yours likes.