Careful on this one

[butlersrangers]

A Krag 1901 rear-sight is on eBay, priced at $149.99 "Buy-Now", by hodd803.

The leaf is definitely for a model 1901 carbine-sight.

On 'zoom' view, the slide/eyepiece looks real sketchy. It appears to be a 1901 rifle peep/slide assembly with a bogus 'C' (circled in yellow) stamped on it.

Photos are real dark and the important left-side of the base is not shown.

Nothing is so confusing as a partially correct Krag sight!

[butlersrangers]

BTW - There is a second model 1901 carbine sight listed on eBay for a 'Buy Now' price of $285, that appears correct.

[Zac952]

Another trick to identifying a proper carbine slide is to look at where the notch is. On carbine sights the notch is squarely in the middle well rifle sights have the notch offset to one side, this was due to the rifles having a tendency to shoot right at longer distances, this was not observed in the shorter barreled carbine so the slide notch was centered.
Just a helpful tip in case someone stamped the c in the correct place to make a deep fake.

[butlersrangers]

'Zac', that is true on model 1898 and model 1902 carbine rear-sights. The notch is in the center of the carbine eye-piece, whereas the rifle notches are off-set.

However, the 1901 rear-sights are a bit different. The rifle leaf has an 'angled track' on the inside edges to shift the eye-piece for bullet drift.
The carbine version of the 1901 sight and the Board of Ordnance & Fortification version are straight, since they showed less drift.
The eye-piece notch is actually centered on the slide of all 1901 sights.
I believe the carbine slide is a bit 'dehorned' to better navigate the saddle-scabbard, hence the "C" marking. (I really need to verify this someday).

[Zac952]

20210520_233623.jpg (521.23 KiB) Viewed 969 times

I maybe have a possible variation then as this came on a 1902 year production rifle and you can notice the notch is offset to the right, I'll have to compare the picture to a current 1901 sight I have as I sold that rifle in the picture, I thought the sight notch was offset on all of the 1901 rifle sights as I measured the difference on that one in the picture compared to a 1901 carbine sight.
You can really notice the offset when compared to the peep plate, which I figured was to compensate so you could center the sight windage and at the B marking it would account for the windage correction and at closer ranges it would be close enough to not matter.

[butlersrangers]

You are right 'Zac', that notch certainly appears offset to the right. Another Krag 'variant' to watch for and explain!
(Attached is a photo of a model 1901 rifle sight that has a 'centered' notch).

The Krag bullet's 'rotational drift' is to the right because of the barrel's clockwise rifling twist.
That is why the model 1901 rifle sight-leaf is machined to shift the eyepiece to the left (as does the 1903 Springfield leaf), as the range increases.

A funny thing is that U.S. Krag rifles were found to have their projectiles leave the bore deviating to the left. This peculiar "drift" to the left, probably caused by action/barrel harmonics, reached its maximum at around 800 yards. (To correct this deviation to the left, the model 1898 and 1902 rifle sights have their notch off-set to the right).
At about 1100 yards, rotational bullet drift brought the projectile back to the 'center-line' and the bullet continued its rotational drift to the right.
U.S. Krag carbines and the 26" barreled Board of Ordnance & Fortifications rifles did not show the extreme deviation to the left or the same degree of rotational bullet drift to the right, that was exhibited by the 30" barrel of the Krag rifle.

I wonder if the off-set notch, that 'Zac' noticed on a model 1901 sight, represents an early variation of this model? I believe most have a centered notch like in the attached photo.

[Zac952]

Maybe it's my eyes playing tricks on me but it appears as if that notch is offset as well, I looked at the 1901 rifle sight on my current rifle and it is also offset, I used the tail on a set of calipers to verify the difference, but ill have to give you a read out later this weekend as my analog calipers are no where to be found and my battery died in my electronic set.
Edit, found a battery, the left side of the sight measures at .269, well the right measures at .229.

[butlersrangers]

Well 'Zac', I'll have to do some careful measuring of my model 1901 rifle-sights, when I get home.
Maybe I've missed something that is in plain sight!

If the model 1901 rifle notch is a bit off-set to the right, this might help compensate for the Krag projectile leaving the rifle bore deviating to the left.

The shift of the eyepiece to the left as it is advanced up the sight leaf would compensate for the rotational bullet drift to the right.

[FredC]

I just checked the 1901 sight that Br sent to me and it measures .246 on the right side and .268 on the left on the primary (100 to 400 notch). When you look for it, it is definitely there.
This is a little deceiving as there is that construction joint on the right with the pin holding it together.
Peep hole to the outside of the base is .299 on the right and .336 on the left
Top notch on the slider is.244 on the right and .266 on the left.
Top notch on the ladder is .281 on the right and .238 on the left.
Measurements were done with a relatively new Starrett electronic caliper.
Better measurements will be done later with a comparator or tool makers microscope. A preliminary glance on the comparator shows both notches and the peep hole are on (three) different center lines, who knew! Better numbers and photos to come.

I checked the carbine sight that I have on hand, not sure of the model but it resembles the rifle sight and it is definitely centered within a very reasonable tolerance.

[butlersrangers]

Thanks 'FredC' for the data on your 1901 rifle sight.
I've long scratched my head on why the 1901 rifle sight addressed bullet 'rotational drift' to the right, but seemed to ignore "harmonics" throwing bullets to the left, when leaving the 30" rifle barrel muzzle.

Now, I'm guessing that I long missed that the 1901 rifle-sight notch and aperture were off-set to the right to compensate for the projectile heading left.

Those Ordnance Enginurds were smart!