Maximum Effect of Parallax

[Xptical]

Hi all.

I'm doing some shooting at 10/15/20 yards.  Mostly 10 yards.  I'm seeing "fliers" from my can of Crosman .177 Hollow Points.  Nothing too concerning there.

What makes me wonder tho, is when I get a sub-group just off my main group.  i.e. 1 flier, 6 on the bull, 3 high and right of the bull.

I'm wondering if my hold is changing forcing a parallax change in my sight picture.  I would not expect parallax to even be an issue at 10 yards, but I'm asking here just in case.

Thanks.

[Artie]

Is it a springer? I shoot from a bench and with a springer, modifying hold or gun support will shift my groups. I don't know if parallax error would move or open up groups though I'm thinking the latter...

[Xptical]

Is it a springer? I shoot from a bench and with a springer, modifying hold or gun support will shift my groups. I don't know if parallax error would move or open up groups though I'm thinking the latter...

QB-78S on CO2 shooting at 10 yards from a bipod.

Honestly, I was expecting a *tiny* group at this range.  I never really shot scoped before, so I can't diagnose the errors.

[Artie]

With co2 I can't imagine why. Parallax is easy enough to detect though. Just do the the head bob with the rifle held fixed on a target, if the reticle shifts in relation to the target, there is a parallax error.

[Motorhead]

10 yards or a 100 ... if the barrel does NOT like the pellet being shot it won't be accurate !!

[starlingassassin]

10 yards or a 100 ... if the barrel does NOT like the pellet being shot it won't be accurate !!

+1

[Roadworthy]

Find the gun's favorite pellet.  Allow adequate time for CO2 pressure to build after each shot.  Parallax is more noticeable at close range than at greater distance.

[Relentless Holiday]

Curious about what scope you have on it?

... and if you have it set up for a real nice cheek weld?

I definitely agree about the pellets but two distinct groups isn't usually what I get from the ones my guns don't like.  I seem to get shotgun sprays. 

The nonspringers (stored air guns: PCP, co2, or pumpers) that have done that to me, with good pellets were ones where I had to scopes were not good fits to the guns.  Not real repeatable cheek weld, or maybe needed to lean in, out or over for a good sight picture.  Using lower rings helped with it on a few of my guns.

I do believe it's parallax possibly.

I also noticed it happened with my shorter scopes .... really compact ones...

[Xptical]

I updated my .sig, but here's the combo:

Beeman QB-78S  .177  w/Centerpoint 4x32 Scope

Crosman 7.4gn Hollow Points


The pellets are always suspect, but I'm still seasoning the barrel.  I expect the occasional flier.  I'm recording between 3 of 25 and 7 of 25 fliers in my groups.  Between 12% and 28%.


This morning, I shot 25 pellets at 10 yards.  The groups were 1 1/8", 3/4", 3/4", 1 5/16", and 3/8".

Group 1 was warm-up.  Groups 2 and 3 are what I normally expect to see.  Group 5 was awesome aside from a single flier.  Group 4 was the worst.


I've looked for a few "best practices" on scoped shooting.  If you know of any articles or videos about scope-specific shooting, please share.  Other than trying to keep everything concentric, I'm clueless.

[Back_Roads]

 If the crosshairs seem to change POA when you bob your head, you can adjust the parallax by turning the front lense of the scope outward a turn or so. Make the adjustment look through your scope at a target move your head if you still get POA change adjust a little more.

[mpbby]

Besides parallax, there are several factors that the inconsistency may be coming from.  When you think you actually may trust 'enough consistency' from your setup and pellet, the shooter has to be "100"% repeatable.

When you have a fixed objective, you will have to be also - repeatable - about the position of your eye relatively to the scope. 

For instance .. Looking through the scope, try back (dark ring appearing in the borders) and forth (entire clear view) until you think your eye is centered with the axis of the scope; that would be the best eye position to be repeated (parallax free).  Your feeling about your cheek touch when the eye is well positioned may help your checklist (previous to each shot).

Hope it helps.

[Xptical]

Looking through the scope, try back (dark ring appearing in the borders) and forth (entire clear view) until you think your eye is centered with the axis of the scope; that would be the best eye position to be repeated (parallax free).  Your feeling about your cheek touch when the eye is well positioned may help your checklist (previous to each shot).

How much "border" do you want to see?  I'm seeing a good bit of solid black border between the scope bezel and the reticle.  There is no close/far shadow, but there is a definite border.

I'm kinda using that black border as a guide.  When I talked about keeping things concentric, I meant keeping the bezel, order, and reticle FOV all centered.

If the crosshairs seem to change POA when you bob your head, you can adjust the parallax by turning the front lense of the scope outward a turn or so. Make the adjustment look through your scope at a target move your head if you still get POA change adjust a little more.

Is that for parallax?  I thought that was a focus thing...

[Relentless Holiday]

Is the scope AO?  scopes that are not will show the effects of parallax more at distances above or below the fixed focal distance (35 yds is my guess on yours)  that is preset by the builder. if you can't adjust the yardage it's fixed. if you can set it for different distances it's AO or Adjustable OBjective or "parallax adjustable. And the effects of different eye position can be greatly reduced by setting the right distance to your target.

The focus ring at your eye should be used to focus the crosshair for your vision then left there. The distance to the target on your scope would be by turning the adjustable front lens only. If it's adjustable...

[mpbby]

I am considering that the Centerpoint 4x32 is NOT adjustable.

"I'm kinda using that black border as a guide.  When I talked about keeping things concentric, I meant keeping the bezel, order, and reticle FOV all centered."

That's the idea.  Then, from the "concentric position" of the eye (parallax free), you should carefully approximate just until you have a clean view (no black border). It seems to me as the best efforts in order to minimize parallax effects.

Anyway, keep in mind the several factors occurring besides any possible residual parallax.  Don't let the parallax idea distract you.

[Relentless Holiday]

Right Marcos!  I was just spelling out what AO was for him he sounds really new to optics.

And Xptical. his advice on assuring you line up the same using the black ring around your field of vision evenly will help a ton.  In fact i like to mount the scope so that i just see a very thin hair of black ring. Then if I am not dead center some of it is missing and i know to adjust.

[Relentless Holiday]

Which brings up this also.  Read this and ask if you have any questions.

www.gatewaytoairguns.org/GTA/index.php?topic=72099.0

It is SUPER IMPORTANT to get this if you want the best from scoped guns. Mounting the scope right is huge especially when you change shooting distances. But holding the gun straight or at least canted exactly the same for 1 distance is absolutely critical.

You may just be canting (tilting) the gun different for each group   

See for yourself. shoot 5 10yd shots as usual. Then shoot five deliberately tilting the gun 45%.  That won't leave any doubts in your mind. And just remember canting the gun just a little will do the same thing, only less.

for about $10 you can but little bubble level that mounts on the sight rail of the gun. It will keep you straight.

The QB78s are crazy accurate. i have only had mine about 6 months. I love it!

[Relentless Holiday]

....And finally how that author suggested mounting the scope with no cant, locking it down and calibrating it all to plumb and level. Read it, learn it live it.  That would be what I did, Inever looked back 
 
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Real Name: Scott Hull

Leveling the scope and gun.
« Reply #7 on: August 04, 2014, 01:37:09 PM »
Quote
The following is a procedure for eliminating both types of cant errors.

Adjust out any scope cant (important for any shot requiring holdover, close or far):
1) Sight in at the trajectory apex (usually 23-32 yards, 25 yards is good)
2) At 10 yards, shoot at a target that has a vertical line on it. Use a plumb line or construction level to insure it's vertical.
3) Rotate the scope in the mounts until all shots hit exactly on the line at 10 yards.
4) recheck the 25 yard zero and repeat until zeroed at 25 yards and on the line at 10 yards.

After that, your scope should be locked down and securely tightened in the rings. If you plan on using a gun mounted bubble level, you still need to adjust that.

Eliminate gun cant (especially important for far shots):
1) line the reticle up with the vertical line on the 10 yard target (or use a plumb line at any distance).
2) Rotate or adjust the gun or scope mounted bubble level until the bubble indicates level while the reticle is still on the plumb line. Lock the bubble level in that position.
3) Make sure the bubble indicates level whenever you shoot.

There is not much point in eliminating gun cant until you are confident that the errors are not related to scope cant. So, adjust out the scope cant first. Scope cant is eliminated by adjusting the scope in the rings. And then gun cant is eliminated by holding the gun and scope level.
« Last Edit: August 04, 2014, 01:47:27 PM by Scotchmo »
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[Xptical]

I did some additional testing over the last few days.

First, I optically centered and mounted the Barska 3-9x32 on the QB-78.

For mounting, I used a small bubble level across the breech loading area and the top turret.  I'll investigate cant later on if it's an issue.

I didn't zero he scope, but I just worked on the fore/aft positioning until I could start to see the "far" shadow inside the FOV.  I moved my head and rifle until the shadow is centered between the bezel and the FOV.

I sent pellet after pellet through a 3/4" area with this setup.

Now, that's not super at 10 yards, but it's light-years better than it was.  It was probably just me the whole time.  I did change from Crosman HPs to Crosman Destroyers.  They are a bit lighter, but I doubt that had a massive effect.



In response to my initial question, the answer (for me) is that head position/parallax is a massive factor even at 10 yards.  I just *have* to ensure my head is absolutely looking straight down the barrel of the scope.

This is all based on the theory that the shadow being centered is a good indicator of head position.  I even moved *way* back on the rifle until the shadow was almost completely filling the FOV and fired a few test shots that way.

[Eddie_E]

My last 2 tins of Premier hollow points in .177 have had some under sized pellets. I'm not fussy enough to measure, but my old Shadow 1000 barrel fits the good pellets easily, but not loose. The fliers feel noticeably loose in the breech and I know they will hit 2 mils high and right every time. My best guess is one of the .177 molds is under-sized, running cold or whatever causes that. All of my .22 Premier  hollow-points group fine.

[starlingassassin]

I did some additional testing over the last few days.

First, I optically centered and mounted the Barska 3-9x32 on the QB-78.

For mounting, I used a small bubble level across the breech loading area and the top turret.  I'll investigate cant later on if it's an issue.

I didn't zero he scope, but I just worked on the fore/aft positioning until I could start to see the "far" shadow inside the FOV.  I moved my head and rifle until the shadow is centered between the bezel and the FOV.

I sent pellet after pellet through a 3/4" area with this setup.

Now, that's not super at 10 yards, but it's light-years better than it was.  It was probably just me the whole time.  I did change from Crosman HPs to Crosman Destroyers.  They are a bit lighter, but I doubt that had a massive effect.



In response to my initial question, the answer (for me) is that head position/parallax is a massive factor even at 10 yards.  I just *have* to ensure my head is absolutely looking straight down the barrel of the scope.

This is all based on the theory that the shadow being centered is a good indicator of head position.  I even moved *way* back on the rifle until the shadow was almost completely filling the FOV and fired a few test shots that way.

once you try the "mirror method" for leveling your scope you'll never do it any other way :-)

but its not for optically centering it,
its used to align your reticle with the bore.

get a mirror ,set it up at say 5yds,set your scope to 10 yds (or when its focused in the mirror)

look through the scope at your reflection in the mirror (a steady gun rest helps)

rotate the scope till the vertical crosshair intersects the barrel when the crosshairs are centered on the scope objective.

"bam" your crosshairs are now aligned with the bore 

then i use a big fishing sinker hanging on a bright colored string to get a vertical line,
move the gun till the vertical crosshair lines up with the string and lock down the scope level,