I just listened to a piece whereby you explained the 25 yard, first cross the line of sight method.
You explain this very well, and how it has changed as scopes have changed. I have always used this and mpbr for my hunting purposes. ( I use lower power , low mounted scopes) .
I don't watch much video or audio stuff and don't have t.v. by choice. I am not a tech savvy guy.
Never had considered any correction for larger power scopes of today, although I have used math to sort out iron sights.
Have you done any audio of sight adjustments on the various types of iron sights? Aperture sight choices , how it works and what to look for to make sight adjustments? Maybe, this is of no interest these days. Cheers

Ok, now you got me confused.

Years ago, I saw a chart that showed the first cross line of sight method for sighting in your rifle. At the time, I strictly hunted with a 30-30 and the chart said to use 23 yds as the sighting in range. Inevitable, I would be out at dusk dark, the evening before deer season opened, sighting in my scope. I used this method and never had a problem with it, but I dont ever remember having to shoot a deer at over 50 yds or so.

If I understood what I read, you are saying that the power of the scope makes that method inaccurate? How does changing the power of the scope make any difference?

comerade,

You must have seen the DVD I did years ago on basic accuracy techniques. I haven't done any more videos, but the major point for your question is the scope height above the bore affects longer-range zero, the reason the 25-yard zero doesn't work as well anymore, since the scope height above the barrel has generally increased with larger scopes.

I published an article on why the 25-yard sight-in doesn't work nearly as well as it used to a while ago, which with additions became a chapter in my 2014 book, MODERN HUNTING OPTICS, available through riflesandrecipes,com. That chapter provides far more information than I can summarize here.

Oldman3,

I can see why you're confused. The problem isn't magnification, which doesn't affect trajectory, but the SIZE of the front and rear bells of modern high-X variables, which affects their height over the bore. Again, all this is explained in my book.

Ahhh...Changing the height of the scope above the bore, makes sense. Thanks!

My point here is , you have an ability to explain things like this really well, John.
I read quite bit , and sometimes I like to hear it.

As an example, I tried to use the 25 yard sight-in method the oldtimers told me about ~35 years ago. Caliber was 30-06 with 180g factory loads. The, scope was a Leupold 3-9x40 mounted as low as possible. Dead on at 25 yards resulted in 8" high at 100 yards. A friend who had a 300 WBY said he experienced the same thing.

Measure your height above bore and use a ballistic calculator to determine where your setup first crosses LOS (zero). I use this method to boresight a new scope by looking down the bore at a target and aligning the scope with it, generally 34 to 38 yards away. Always on paper at 100 yards which is the goal. I might shoot one or two shots at home to confirm before heading to the range just to confirm.

In the article (and book chapter) I suggest sighting-in an inch low at 25 yards works far better as an initial zero--which usually results in about a 35-yard zero.

Another thing I mention is that a 25-METER sight-in is taught in at least one of the South African professional hunter schools. I found this out on a 2003 safari, when the assistant PH was a recent graduate of the school. He took our group to the ranch range, where he had a target set up at 25 meters (a little over 27 yards), and insisted it would work fine. I tried (mildly) to correct him, but that obviously wasn't happening. So I deliberately held an inch over the bullseye--but just about everybody else's rifle shot too high in the field, and had to be corrected. Four years later I hunted with the same young PH on another ranch, who by that time was out on his own. He took our group to the range he'd set up--which turned out to be 100 meters, not 25. I didn't say anything, but he looked at me and grinned.

Another problem with the 25-yard sight-in (or any trajectory calculation involving the height of the scope) is that even many hunters who measure scope-height do it wrong. The usual mistake is measuring to the bottom of the scope, not the centerline. In fact a lot of people somehow can't figure out how to measure height to the centerline even when that's what they're trying for. Don't know what's so complex about it, but have seen that a number of times.

MD, I'm confused again.

In the post about the South African professional hunter, you stated that you held about 1" high at 25 meters and I'm assuming you didn't have to adjust you scope, like most of them did.

Shouldn't that have been approx. 1" below the bullseye? If you sight in at 25 meters and your high at 100, shooting high at 25 is only going to make you higher at 100.

Or am I completely screwed up?

You're completely screw up! :-)

I held the creticle of my scope an inch above the center of the bullseye at 25 meters, and when my shot centered the bullseye, that meant I was "zeroed" an inch low at that range.

That was too easy.
Glad you didn't pass it up!
All in good fun !

Yeah, except I didn't proof-read it very well before hitting "post reply"!

I usually blame it on dysphlangia............

Well played....

I like to take a 25 yard shot at the range when I'm zeroed. Then, I know what a 100 yard zero looks like at 25. If i need to check zero, a stump or knothole at 25 is easy enough offhand.
Just to know you are not too bad. Until you can do better.

Hey, I'm a dummy and I admit it.....

MD, when you said you held an inch over the bullseye, I thought you hit an inch over. I didn't connect the dots of aiming an inch high, hitting the bullseye, and not having to adjust your scope.

As the kids use to say, "My bad".

The easier way would be to hold dead on and adjust the scope to hit an inch low.

Some people just complicate things.

Ted

Yukoner,

You apparently missed the context of WHY I held an inch high....

I think I got it, John. That's why I added the wink. Reading it again, my tongue-in-cheek comment about complicating things was not needed. Either that, or that's where the wink should have been.

Larger diameter objectives need the scope mounted higher above the bore. That alters trajectory enough that the POI at 25 yards needs to be changed. It's not hard to understand if one tries to visualize what would happen if the scope were mounted, say, six inches above the bore.

As well, because trajectories are parabolic, it also gives a slightly longer dead-on-hold distance if I am understanding this correctly.

For the past fifty years or so, have always sighted my hunting rifles three inches high at 100 yards, regardless of what I was shooting. Whether it is a 270Win or 300 Mag at 3200 fps, or a 303 Br or 9.3X62 at 2400.

The DOH distance certainly changes, but that setup makes the most of the particular round's trajectory.

Ted

It is a good conversation, and not really complicated, yet I hadn't given it much thought.
My scopes are more streamline and lower powered and mounted low.
I first read about the 25 yard zero from JOC, I was just a kid. It puts you on the paper one yards and that is where the magic happens( or not)
Hey, I even bore sight my levergun.
I use the MPBR method for my big game hunting.
Thanks John for pointing out the new reality with high magnification scopes

With most of my rifles I can sight in about 1.25" low at 25 yards and I'll be close to 2.5/3.0" high at 100 yards. I don't have any scopes with large objective bells so it's worked just fine for me for many years.
Paul B.