Home Forums Hunting & Shooting Ask The Gunwriters "25 Yard sight-in and Related Myths"

4-5 years ago there was a nasty tom cat hanging around the farm. It was just a mean old cat.

One day I spied the sonuvabitch about 50 yards from my parents house.

Had a 300 WSM in my pickup so I got out and snuck up to about 25 yards.

Held dead on his nose and fired a 180 Partition.



Pieces of fluffy white and orange hair floated in the air for several seconds.

Upon examination I hit about a 1/4" away from where I was aiming.



All I remember is BOOM! Forgot ear plugs and I was shooting right next to an 8' windbreak.


My mom was in the house, asked WTF was that?!

Neighbor 1/2 mile away called up, it was funny.

Did the partition over-penetrate?

nighthawk,

I've had Sierra Infinity for a number of years, used it to figure some of the trajectories accompanying the article, but also mentioned the excellent program Bryan Litz includes with his book APPLIED BALLISTICS FOR LONG-RANGE SHOOTING, which is even more flexible, plus a free on-line program that (like most) has a default scope height of 1.5", but can also be adjusted. Can't remember it's name but it works too. I found it within a minute by Googling the Internet.

That was one of my points in the article. There's no reason to depend on ancient and faulty information with the much more realistic ballistic data out there today.

It's just simple math- If you sight in at 25 yards, at 50 yards the line of sight will be the same distance BELOW the line of bore as the scope is above the centerline of the barrel. At 100 yards, the line of site will be three times as far below the line of the bore as the distance the scope is above the centerline of the barrel.

Up until people started using the big 56mm objectives, the 1.5 inch figure wasn't far off. Even a 40mm objective scope could sit close to 1.5 inches. Since I use small scopes and mount them low, most of my hunting rifles are under 1.5 with the lowest being a set of old Sako low rings on a 579 which put the scope at about 1.3. Most of the others use low Weavers and end up at just over 1.4. Even most of my "F" class rifles are around the 1.7 inch mark. Still, putting updated information out there is valuable and much more useful to people if they just file the information away rather than arguing with it!
Ultimately, nothing beats shooting to become familiar with what your rifle and ammunition will do. GD

One of my rifles mentioned in the article is a custom 1903 Springfield made before WWII by Frank Pachmayr. It has a Lyman Alaskan in a Griffin & Howe side-mount, centered only 1.3" above the bore. Back then a scope 1.5" over the bore was pretty high!

Low Weavers will put most scopes about 1.5" over the bore, but not with most mounts and scopes today. I measured a bunch of scopes on rifles belonging to various people and the average is now around 1.75".

The scopes that were 1.8" over the bore at Gunsite were 3-9x40 Redfields mounted on Ruger Americans, and nobody mentioned them seeming very extra-high. But as noted, we only started sighting-in at 25, then corrected to 2" high at 100, and shot them all out to 400 to see exactly where they shot.

Where might I read this article?

If they can?

I enjoyed the article. What is the best way to measure the height of the scope over the bore?

It's not always possible at every rifle range. I'll be hunting elk out west this fall. My current state-run range (Missouri) only goes out to 100 yards. I'll be moving in June, and I think I'll get to use a public-ish range at Quantico, but it may not go out to 400 yards either. Out west I think it's no problem to find a sufficient range (or just go out in the desert in Nevada), but that's not always the case.

Got the premise of the article.

I'm an old stick in the mud. While I generally "eyeball" the scope/bore alignment as the starting point (yeah, usually on our 25 yard range), once the sumbitch hits to POA, I move off to the 100 and continue, picking whatever zero suits me for that cartridge.

If I want to know exactly where it hits at 200, I shoot it at 200, same for 300 and so on. Although I've stumbled onto the deal that some cartridges need to be zeroed at say 1.5" to 2" high at 100, if'n I want it to be "on" at 200 or 250?

One of my 25-06s has a finger adjustable elevation turret that's been sorted out for the 100 yard zero, marked for longer ranges and is dead on and repeatable out to 500 yards.

Another one is zeroed 2" high at 100, appears to be dead nutz at 250 yards, as a few DRT deer can attest. When I did more longer distance varmint killing, paid lots more attention to calculating trajectories and such for loads. But I haven't changed loads for some time.

Should probably get back to that again and stop "guessing"?

You'd shoot at an elk at 400 with a rifle you'd only shot at 100?

hidalgo,

I mentioned the easiest way in the article: Measure from the mid-line of the objective bell (you can measure the bell and make mark in the center, if you're not confident enough in eye-balling it) to the top edge of the stock--which is almost always right along the center-line of the barrel.

"Line of sight" distance from the "line of bore" doesn't translate directly to BULLET height at a given distance .
"Line of bore" remains a straight line, while the bullet follows a parabollic path that is below the "line of bore" most of the flight

Read the article a few days ago and reminded me of when I first shot a centerfire. A new 336 in 30-30, went for the "25 yd zero will do it" concept which shortly found it put me somewhere on the berm at 100. First and last time I believed concepts bandied about like writings from the Bible.

Now I zero at 200 meters and work back to 100 mtrs, 100 yards then 50 yards, work with an online calculator one evening and set up a chart after matching what actually works. Not too worried about beyond 200 meters, that has usually been my limit in hunting, usually way closer anyway.

With my 30-06, that I have used exclusively in the field for 10 years to take elk and deer, mostly yes. I wouldn't shoot at any animal in other-than-ideal conditions further than about 275 or 300 yards. But I would surely take a 275 yard shot at an elk after having only shot at 100 yards for the last year.

I should add at my last duty station I had access to a range that I could shoot to 485 yards, so I know I and my rifle's hunting range capability. However, I have taken the scope off my rifle this year to realign the crosshairs. Does that mean I'm unethical to shoot at an elk to 300 yards with the rifle, after only shooting to a max range of 100 yards? Preposterous!

However, I do have a 25-06 with a new barrel. I don't have nearly the history with the 25-06. I would likely not take a long poke with the 25-06 until I learn a bit more about her and the expected outcome.

It's a good thing to have a decade-long relationship with one rifle. I can only expect it to get better...

I'd say a good number of the elk hunters out there do exactly this. Possibly even a majority.

Pretty crazy, but that's the way it is.

I'd add that it's likely the majority of deer hunters do the same, with many just guessing about the 100 yds and not really measuring anything

At the distances at which most deer are killed it hardly matters

This isn't a good thing. Many, many animals are wounded and lost because of yahoos having no idea what they are doing.

I read Jack O'Connor avidly as a youngster. When I got my first rifles I rough sighted at 25 yards and tried for the good old 3" high at 100. I commenced blowing holes in the scenery over the top of game animals. My dad finally grabbed the rifle, cranked the scope down a couple of inches and told me to leave it alone. Nailed the next buck I shot at. Then I started getting smarter about trajectory, got over my 10 yr old's buck fever complex and started paying more attention to how things actually shot over various ranges.

These days I purposely bore sight below center. I head for the range and rough sight initially for one inch low at 25. That usually gets close to where I want it at 100. When I get there I shoot further and see what shoots where.

I found out that if you are going to rely on the 25 yard zero (the one inch low version) you have to be pretty precise. Just today I was changing the sight in on my 243 from the 95 gr NBT I hunt deer with to the 55 gr NBT that is my ranch rifle varmint load. That 55 shot three into the same hole at 25, but just a tad high. No problem because next stop was 100 yards. First shot, I couldn't see a bullet hole. By the third shot it was obvious I was hitting at the top of the target page, about 8" over the aim point. Little errors in close can be disastrous out from the muzzle a ways. As a kid I took Jack O'Connor as gospel. That and published ballistics tables and trajectory charts. Ground truth rules, which I learned the hard way.

Ground squirrels are up so there'll be some more ground truth later.