Home Forums Hunting & Shooting Ask The Gunwriters Why would a rifle shoot 1/2 MOA at 100 and 2 MOA at 200 yd???

There are a bunch of books, both old and new, that should be required reading--if that means acquiring an understanding of what actually happens when a rifle goes bang, and how much riflery has advanced (or even repeated itself) over the decades, and how many of the "common beliefs" many shooters still have are mistaken, though they may have been at least partly true in the past. Bryan Litz's books should also be "required reading."

MD,
Agree, but at what point with all the advances do we eliminate the old adage of tuning the load to the rifle to a more appropriate term of tuning the rifle to the shooter? Not trying to be PC, Valid question. Have seen more than once where the rifle was better than the driver.

That's always the basic conflict.

I should have added: especially in 24hour Campfire questions about: "What's going on with my damn rifle?"

Easy, the nut behind the butt. Next question.

Yes. the maximum parallax error E at a given target distance t for a scope which is parallax-free at distance p and has an objective lens diameter D is given by the equation

E = 0.5 D (abs(t-p))/p

So, for example, if you have a scope with a 40 mm objective lens, parallax free at 150 yards, maximum parallax error at 200 is

E= 0.5x40 (abs(200-150))/150

=6 2/3 mm

Similarly, for a target at 100

E= 0.5x40 (abs(100-150))/150

=6 2/3 mm

That is to say, if your eye position is at the edge of the exit pupil, you could be as much as 6 2/3 mm off at these distances, in these particular examples.

Dan,

Yep, exactly--but there are many assumptions in parallax calculations, especially that the shooter can recognize it. Many don't. Country boy only states that he adjusted the rear focus on the scopes, which may indicate he doesn't know how to check for parallax. I asked him specifically about that at one point, but he never really responded.

Unless I missed some other details (this thread has gone on for a long time) he wrote he used a "Leupold 5HD" and a "Conquest" scope. He does not specify the magnification or objective lens size of either, so there could be far more parallax than you're assuming, especially assuming a scope parallax-free at 150 yards.

Add a little wind-drift to more parallax than the possibility you used as an example, and there could easily be 2+ inches of error at 200 yards.

I was answering Youper's question, not country boy's, in that post.

FWIW though I raised the question with country boy earlier about adjusting the eyepiece focus rather than parallax, and he confirmed that he was both aware of the difference between eyepiece focus and parallax adjustment, and that he had adjusted for parallax.



I made the point earlier that I didn't think that parallax was the sole problem, if it was the problem at all. There are a range of other possibilities, including wind, and including the possibility that a number of issues, perhaps including parallax, are combining to produce the observed result.

Dan,

What he posted was, "I made sure the reticle was focused and checked for any apparent parallax issues, but did not see any." He did not state whether he did this at both 100 and 200 yards. A lot of shooters assume that once the reticle's in focus, there is no parallax.

He has also never stated the magnification, objective lens diameter, etc. of either scope. All of which would have some bearing in the question, even if the reticle's in focus. Have seen considerable parallax with a 5-15x German scope at 200 yards when set on 15x and the reticle's in focus.

And the graduations on the parrallax adjustment don't seem to always align correctly with the actual distance.

I have several high end scopes I shoot with. I start adjusting to eliminate parallax error at the yardage I am shooting. When the target is brought into sharp focus using the parallax adjustment I know two things:

1. I am close, but there is still parallax error; I can induce it by moving my eye that is peering through the ocular and watch the reticle move around on the target although the rifle and scope are not moving...only the position of my eye relative to what part of the ocular lens I am looking through. I need to continue to adjust the parallax knob.

2. The final image, as near parallax free as I can get it, is, for me, always slightly blurred. Could be my eyes...I require corrective lenses to see "20/20".

I thought I had added this info, but I can't even keep up with this thread now.
The first scope was a leupold vx5 3-15x44. It has a side focus knob and an eyepiece adjustment ring.
The 2nd scope is a Zeiss Conquest 3-9x40. It only has the eyepiece adjustment ring.
I checked for parallax at 100 and 200 with the vx5 and found none. I did not check the zeiss as it has been excellent on another rifle for several yrs, but I will check it on my next range trip. I shot both scopes on maximum power.

Country boy,

Yes, this thread has gone on a long time. I missed where you described how you checked for parallax at both 100 and 200.

I'm coming to the conclusion that the rifle is possessed by demons. Haven't seen many rifles that are, but there have been a few over the years....

Have also come to the conclusion that I need to quit responding to any "Why doesn't my rifle shoot?" threads if they go on more than a maybe 20-30 other responses. Apparently beyond that point I don't care enough anymore to carefully recheck every response.

In fairness to you MD, this is actually the second thread on the issue, after some static from one of the contributors in its first outing. It is a good example though of how if a "why doesn't my rifle shoot" goes on for very long things get repeated, issues that were dealt with come up again, and it can be hard for anyone to keep track of where we're up to.

Thanks, Dan. That clears some things up. But I have often found "why doesn't my rifle shoot" threads to be something like chasing invisible rats down an endless hole.

All too often there's something really simple wrong with the rifle--though not always obvious. Earlier I mentioned a question from a member on a good load for 165's from a .30-06. I gave him my standard answer, around 58 grains of H4350, but it didn't shoot, even after he changed scopes. Six months later he contacted me, and it turned out he'd tried two brand-new scopes. Both were bad. With an old proven scope the rifle shot under an inch.

Another time went through a bunch of stuff with a question about a custom rifle that didn't shoot. After quite a few posts, from the OP and me and others, it turned out he hadn't tightened the scope bases down.

I find it easier to glass bed, freefloat, fine tune a trigger and work up a good load that easily shoots moa, than it is to follow some of these threads. This one was funny because the OP seemed to be tight lipped about a lot of things. You basically had to beat the info out of him, with repetitive questions. He's yet to post any pics too (like I asked for multiple times). A lot of these guys are here to help, but when the op has to be asked 5 times what kind of scope or how its mounted, it kind of gets tiring...For example, finally on page 12 of this thread, he finally tells us the scope is a VX5 3-15x44. Before that, it was just a "VX5". From that info, we know it's a parallax adjustable scope and generally of good quality. However, it's still not a "proven" rifle scope. If these guys would just take a little time and establish a rock solid foundation (glass bedding), tune the trigger, sufficiently freefloat their barrels, USE a PROVEN rifle scope, ensure their ammo is concentric and work up a good accurate moa load, there would be far far less of these threads. However, some guys think they can just take a bone stock rifle out of the box, have a store clerk mount a scope for them and be shooting lights out at the range that same day with factory ammo. That rarely happens, and for how long is it going to keep doing it? Who knows: Did the store clerk use loctite on the base screws or even torque them down properly. Did he make sure the base screws were of the appropriate length? Personally, I still believe the OP's "1/2 moa" rifle has not even proven to me it's a moa rifle at 100 yards. I'd need to see many many multiple 10 shot groups to verify it's a moa capable rifle. Even if it's only shot at 100 yards. Shoot some 10 shot moa groups at 100 yards and I'll guarantee its going to shoot well at 200, 300,400, etc. etc.. I've done it thousands of times, to know it's going to happen that way.. The secret is knowing you have a proven and capable set-up. You don't just fire off a couple 3, 4 or 5 shot groups that are 3/4" to 1 1/4" and say, ok, it's an MOA rifle now. Show me multiple targets, make me a believer. This just hasn't happened yet in this thread...

MD, regardless of how this turns out, I've learned a lot from this thread. Thanks for your assistance. I hope to shoot again this weekend and I hope I have plenty of time so I can work through some of the suggestions. My thought from the very beginning was that the problem was the scope or the trigger puller. I'm starting to think it's the latter......

Thanks again.

You're welcome. Will still be very interested in hearing how it turned out--especially if the rifle's not possessed by demons!

BSA, my apologies for asking for help prior to shooting at least 1000 rounds. I'll wait a little longer next time I have a question.
Yes, my post was initially vague on purpose because I was looking for generic answers and I didn't want people jumping to conclusions based on brand names that don't have a good reputation, etc. I also wanted to protect the individuals that I bought the rifle and scope from. I'm not blaming them for anything and I hope others don't either. I see now that was the wrong approach.

Yes, my first thread in the hunting rifles forum was derailed by a jacka$$, and I copied my post to here where most people have been helpful, even if a little condescending.
I haven't posted pics cause I didn't take any. I made notes and moved on. Maybe I should from now on.
I didn't post all the details because I didn't know what was relevant. As I said, I've learned a lot here.
Also, I mounted the scopes myself. Never have or will let a "store clerk" mount a scope for me.

Thanks. So it sounds like the maximum in this example that parallax alone could add to a group at 100 or 200 yds. is about 1/2".