Have you adjusted the “fast focus” or “eye-piece” focus?  That's the part near your eye that should bring your reticle into sharp focus. 

Yes, I employed the “fast focus” eye-piece to focus the reticle. I am extremely presbyopic (or far sighted), so I doubt that the average shooter who picks up my rifle would find the reticle in sharp focus for them. But I don't think that has anything to do with bringing the target into focus. There is print aplenty on my targets to focus on if I were only able to do so.

I don't see much difference in parallax inside 600 yards

Robert, do you have this same scope? If so, are you saying that your experience is the same as mine? Are you able to bring the target into “sharp focus” using the side focus knob? When you shift your eye position slightly (either side-to-side or up-and-down), do you see the reticle move in relation to the target?

The Adjustable Objective is strictly for dialing out parallax error.  It's not suppose to be used for focus.  As Jacob Bynum says “Focus is a byproduct”

Using the name Jacob Bynum as my search parameters, I was able to discover that he is a shooting instructor. Sounds like a fella could learn a great deal in one of those classes! As far as how to use the side focus knob, the Vortex Riflescope manual saith:

• Focus the reticle (paraphrased)–did that
• “Turn the side focus knob until the target image is as sharp as possible. The yardage numbers referenced on knob should closely match the actual yardage to the target.”
• “Check for parallax error by moving your head back and forth while looking through the scope. The focus is correct if there is no apparent shift of the reticle on the target. If you notice any shift, adjust the focus knob slightly until all the shift is eliminated.”

I guess what I'm trying to understand is the proper procedure for parallax adjustment. JB says focus is but a “byproduct”, but my manual spells out a procedure. And the procedure starts with bringing the target into sharp focus.

What I've observed, thus far, is that:

• my target never does come into “sharp” focus
• the preponderance of the focus range (~50-500) is about equally “focused”
• it takes me a really long time and a lot of twiddling to find a point at which (if ever!) the parallax error has been adjusted out
• when I believe that I've finally found a point where the parallax error is gone, the numbers

do not match (not even close, really) the known distance at which I am shooting

I spoke to Vortex Customer Care about this, and they seem to think that the parallax adjustment on my scope is not functioning correctly. Really nice folks out there! As I've been led to believe, it appears they are going to take good care of me on this issue.

I intend to take the rifle to the range one more time to see if I've made any improvement in my precision by removing the “nubbins” from the Tikka synthetic stock. While I'm at it, I'll continue to try and figger out the parallax adjustment a little better. Baring any last minute epiphanies, I guess I'll be taking it off and sending it back. I'll update this post after my next range visit.

I've got two threads that seem to be converging, now. Rather than update both threads, I'm going to try posting a link to my other thread here:
https://tikkashooters.com/public_html/general-discussion/hunting-the-sub-in-'sub-moa'/

Well, I thought I would put this thread to bed for good. I did send the scope back to Vortex for service. Long story short, while it cost me nothing (but time), it came back to me no better than it was before. After describing the issue in detail to their service personnel, their best recommendation was to try either their 2-10 or 6-24×50 models, both of which have “superior image resolution” compared to the 4-16×50. It seems that they have some familiarity with this issue. In fact, I found, quite too late, that the Vortex Viper PST 4-16×50 has something of a reputation for “inferior glass”.
http://www.opticstalk.com/vortex-viper-pst-vs-weaver-tactical-opinions_topic28963.html
And there are other similar threads. To their credit, Vortex has offered me a refund on their scope. So I've purchased a Weaver Tactical 3-15×50. Hopefully, I will find, as apparently many others have, that the Weaver glass is superior. This is my first experience with a long range AO scope, which I purchased primarily for learning the long range rifle craft. And I have indeed learnt a thing or two!

OK, I finally got to visit the range today with my new Weaver Tactical 3-15×50 scope. The first observation I can report is that the glass definitely provides “superior image resolution” as compared to the previous Vortex 4-16×50 scope. I easily obtained zero in about 2 shots from the 25 using the bore sighting method, so that's a positive, too. And with the “superior” glass, I now find that I can, in fact, dial the parallax adjustment knob until the target image is sharp and crisp. So my major complaint with the previous scope is resolved.

And now to touch some negative and “mixed reviews” items. I find the “eye box” is really fussy on this scope compared to the Vortex scope. I suppose it might be that the exit pupil is smaller (though that sort of thing is usually published)? I think I may eventually miss the fact that I don't have a zero stop on the Weaver scope. The Vortex shim stop is arguably kinda kludgy, but at least they have one. Even with a 20 MOA base, I find that I have about 2.5 turns (12 mils?) below my zero. Like other Weaver users, the pop-up locking turrets sometimes don't want to pop back down without a little bit of fiddling. I prefer the Vortex reticle design over the Weaver, though it still has to be an improvement over the original mil-dot reticle the military developed. One nice touch is that the center of the cross hairs is left open, making it easier to tell when the reticle is precisely centered over the POA, especially if the target has an open center, as mine did today. I did the “shoot the box” drill with this scope, and at first blush, I thought it passed with flying colors. I immediately found that the elevation clicks were spot on (0.36″/.1 mil). However, when I got home and measured the windage, I found that I got somewhere between 0.31 and 0.34 inches/.1 mil, or as much as 14% error. I suppose something like that would deeply disturb the purist. But in my view, any windage adjustments are going to be guesstimates to begin with, which will no doubt introduce errors that will dwarf this one in magnitude. And none of it matters if I've got a good spotter to walk me in. (Maybe a bit wishful thinking that last bit… 😉 Still, I find it really cool to shoot 4 3-shot groups at a single POA resulting in 4 targets with nicely placed, tight groups in each.

Finally, I would have to say that, compared to my previous range trips, my groups have gotten better. In my previous trips with the Vortex scope, my mean 3-shot group size was probably 1-1/8″. On this trip, my mean group size was about 3/4″ with my best at 1/2″ and 3 others were about 5/8″. My worst were, well, they were shooter errors! So there is nothing to learn about my rifle from those!

One more new piece of information is that I found another ammo that my rifle likes pretty well. Silver State Armory 175 gr. HPBT Match ammo cost me about $22/20 at Cabelas. Most of the other match ammo that I was shooting cost considerably more and didn't perform any better. One thing is for sure, though, unlike my last one in .270, this Tikka T3 in .308 don't much like the Winchester PowerPoint and Remington Core-Lokt “deer” rounds very much! Those were the worst groups of the day, hands down.