A parallax question for veteran shooters

[ballistictip2506]

Hi guys and thanks in advance for your input. I'm shooting a 2.5 to 10 LPS Leupold that does not have a parallax adjustment. its a wonderful scope but does have its limitations past 300 yards. It's my primary predator rig that's called on for double duty on occasion. The gun is an accurized 700 that shoots an honest 3/4 minute to my 250 yard zero with my deer loads. The groups do open up some as I get out to the 500 yard realm and I can only assume in this particular case that parallax is at least a major contributor to the issue. My question to you is "have you ever been able to qualify and/or quantify your medium distance shooting as far as fixed parallax vs. adjustable parallax scopes are concerned ? ". In other words can you share what you have discovered ,in your experience , in your changes in POI with scopes that do and do not have parallax adjustment features in the mid range arena ? Like most scopes this one is set at the factory at 150 yards. Again thanks.

 

[Bart B]

The accuracy you get at 500 won't be the same MOA number that's at 250; they get bigger in subtended angle as range increases. As long as you aiming eye's on the optical axis center, there will be no parallax.

 

[Clark]

My groups "get bigger in subtended angle as range increases".
I can hit a 1 moa target at 100y, but it is a hail Mary for me to shoot at a 2 moa kill zone at 600 yards.
And the 32 moa moon is much harder than it looks.

 

[Long Time Long Ranger]

A top shooter can shoot a scope with no paralax adjustment just fine. I have shot some great groups the past two weeks out to 1000 yards without a paralax adjustment. You must insure your eye is perfectly centered in the scope. Move your eye in and out and side to side until you get the full field of view in the scope. Your eye will be centered. Do it a few times until you get accustomed to it and your eye naturally going to the center. Watch the reticle move as you move your eye. Just like shooting a bow your eye will adjust to doing the same thing every time. It takes a lot of practice but is doable.

 

[ballistictip2506]

I think some of you guys misunderstood the question. I'm not talking about subtension but rather realistic POI changes from a non adjustable scope vs. an adjustable one ( at the 500 yard mark ). In other words if I employ good bench practices I can blame my load for spreading out rather than my shooting.

 

[Bart B]

I continue to wonder why scope companies and rifle shooters quit calling the process of adusting the front lens group to "focus" on the target the "focus adjustment" or "range focus" made with an "adjustable objective" to parallax adjustment. 'Specially when one's eye is dead center on the scope's optical axis there absolutely no parallax regardless of where the objective's focused at. That front lens works exactly like a camera lens focusing a distant object's image on the reticule plane instead of on film or sensor in a camera.

 

[Bart B]

I'm not talking about subtension but rather realistic POI changes from a non adjustable scope vs. an adjustable one ( at the 500 yard mark ). In other words if I employ good bench practices I can blame my load for spreading out rather than my shooting.

If there's a point of impact change at a longer range (other than what's caused by bullet drop and normal enlargement in MOA), your scope's got something loose inside. There's ways to test it with a collimator stuck in the muzzle, otherwise you may want to send it back to its maker.

 

[1100 Remington Man]

I have a 3.5 x 10 40mm VX 3 I had the parallax changed from 150 yds to 200 yds and at 500 yds it went from max parallax 1.8 to 1.2 inches a improvement of a whopping .6 inch. But if you keep the ( Nut ) your head centered no error is correct. Just a little FYI at 800 yds it went from 3.4 to 2.4 a gain of one inch.

 

[Bart B]

I had the parallax changed from 150 yds to 200 yds and at 500 yds it went from max parallax 1.8 to 1.2 inches a improvement of a whopping .6 inch.

Never heard of this stuff.

Are you saying the maximum reticule shift on the 500 yard target from eye movement, after focusing the scope from 150 to 200 yards, went from 1.8 inches down to 1.2 inches?

How did you measure it to get 1/10th inch resolution?

It's confusing to me when you first say parallax was changed 50 yards then later say it changed 6/10ths of an inch some 300 yards further away.

 

[Greyfox]

I have done a lot of 500 yard shooting with my Mil spec 308 using Leupold scopes with and without parallax adjustments. The fixed parallax scopes were factory adjusted to 150 yards. It's not very acientific but my typical group size measured on multiple outings using my Mark 4 and adjusting for parallax was 3" max at 500 yards. Using Leupold VX3 in 3.5x10 and a VX3 in 4.5x14, the groups were the same as those using my Mk4. Frankly, i was unable to detect much if any parallax movement of the crosshair with the non adjustable scopes by moving my head around at that range. Using the Mark 4, unless I was at the extreme ends of adjustment, parallax determination was difficult to finely adjust and found that image focus was more of a dominant factor. I do make a strong effort to use a consistent cheek weld with my eye centered in the scope which will elimate parallax effects if they do exist. For mid range hunting. I actually prefer a non adjustable scope. One less thing to be concerned with. My favorite scope is a Nightforce 2.5x10. I'm not sure what's going on in the OP's case, but I would think that if proper shooting form is being used, accuracy degradation is likely coming from somewhere else. At magnifications of 15x and above parallax adjustment start to become a lot more critical. IMHO.

 

[Clark]

The eye does not stay lined up with the scope tube, but with the erector.

In this boring 1 minute video of mine, you can see the image start to be occluded, from the point of view of a fixed camera position, when I crank on the turrets.

[ame=http://www.youtube.com/watch?v=pjIL8TTGoIk]002 good up and down but at 8.5 X .MOV - YouTube[/ame]

To get the camera to line up, I mounted it on a x-y rack and pinion from a scrapped out microscope.

 

[Bart B]

The eye does not stay lined up with the scope tube, but with the erector.

OK, I'll put on my optical hat.

The erector tube's optical axis is rarely aligned with the scope tube's axis. As that tube is cocked at some angle off the scope's tube (and objective lens optical) axis so the desired aiming point in the target's image is centered on the reticule. Nothing behind the eyepiece ever gets aligned with it.

Fact is, the eyepiece optical axis is fixed in place on reticule centers when the reticule is between the eyepiece lens and erector/zoom lenses. Therefore, the aiming eye is in line with the eyepiece optical axis that also goes through the reticule center in such scopes. Otherwise, reticules so positioned at this place would never stay centered in the field of view.

 

[1100 Remington Man]

How I came up with the parallax errors to the .1 is I called Leupold and they have a parallax calicator & told me what it is. I was also concerned with Parallax error at long range & since I was haveing a windage dial Installed on my CDS 3.5x 10 40mm why not change parallax to 200 since the range I sight in at is 200 yds

 

[Bart B]

I was also concerned with Parallax error at long range & since I was haveing a windage dial Installed on my CDS 3.5x 10 40mm why not change parallax to 200 since the range I sight in at is 200 yds

Nothing on that scope adjusts parallax. You adjust parallax by moving your aiming eye about the scope's exit pupil.

There is a side knob for setting the range it focuses at.