Deviation and Drift

Ammunition, reloading, shooting, etc
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butlersrangers
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Deviation and Drift

Post by butlersrangers » Mon Nov 16, 2020 3:23 am

In the past, I have posted information on sight experiments conducted by the Ordnance Department, from around 1900.
It was discovered that bullets departed the (30 inch) Krag rifle bore angled or deviating to the left of the line of sight.

This reached a maximum deviation of about 8.5 inches at 600 yards.
Beyond that distance, 'rotational' bullet drift (which had been going on all along) started to bring the projectile back toward the line of sight.
At around 1,100 yards, the bullet crossed the line of sight and continued to drift right till the end of its flight.

This peculiar 'horizontal' pattern of bullet movement was attributed to the Krag rifle's barrel/receiver vibrations. It was thought to be exacerbated by asymmetry and the single lug 'lock-up'.

Ironically, Krag carbines and the (26 inch barrel) BoOF rifles did not show the same extremes of behavior.

Today, I was looking for information in a reprint of "Rules for Management of the U. S. Magazine Rifle - model of 1903", originally published in 1909.

Lo and Behold! The 'symmetrical dual locking-lug' 1903 Springfield, also threw curve balls ... but not as severe ... about 1/2 inch to the left at 300 yards and back to the line of sight at 500 yards.

Attached are the tables from an 1898 Krag manual (1917 printing) and 1903 Springfield rifle manual (1909 printing) showing the data.
Attachments
deviation and drift - Krag.jpg
deviation and drift - Krag.jpg (226.73 KiB) Viewed 168 times
deviation and drift 1903 Springfield..jpg
deviation and drift 1903 Springfield..jpg (196.44 KiB) Viewed 170 times

Hamish
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Re: Deviation and Drift

Post by Hamish » Sun Nov 22, 2020 5:12 am

I have always suspected that the extractor may be involved.

FredC
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Re: Deviation and Drift

Post by FredC » Mon Nov 23, 2020 3:28 pm

Most other rifles have an "unbalanced" extractor. Very few point to that as causing a deviation.
With high speed cameras today it would be possible to view a number of Krags being fired and learn what was happening, My first guess is some combination of length of the barrel past the last band and the weight of the bayonet lug was the cause. I was asked by a local target shooter to make an adjustable weight for his shooting. He wanted it secured to the barrel and with the weight portion on threads so he could look for a sweet spot as far as repeatability.
For SA to find the need for the windage adjustment the rifles would have mostly had the same deviation. Kind of hard to fathom that many rifles would have identical characteristics and the carbines did not. We have since learned that SA achieved a very high degree of interchange ability by making components to very exact tolerances. Well this is my best guess today. I will change it if a better theory comes along.

I have seen some examples of barrel whip posted on youtube. Maybe some else has time to find a couple and post links.

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butlersrangers
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Re: Deviation and Drift

Post by butlersrangers » Mon Nov 23, 2020 9:28 pm

I wish I could speak and read Norwegian.

I wonder if the Norwegians experienced the same phenomena of the extreme left deviation in their model 1894 Krag rifles?

There is a lot of similarity between the U.S. and Norwegian long rifles.

Some significant differences between rifles:

6.5 X 55 mm rimless Norwegian cartridge vs. .30 U.S.A. rimmed (.30-40).

Norwegian rifle - Bolt fitted, so that the rear of 'guide'-rib was in contact with receiver wall.

Norwegian rifle - A vertical screw anchored the barrel to the stock, just in front of the receiver.
(I wonder if Springfield Armory ever tried this)?

Knute1
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Re: Deviation and Drift

Post by Knute1 » Mon Nov 23, 2020 11:42 pm

Here is an 1894 Army and Navy Journal article about the Krag Jorgensen rifle for Denmark. It has a statement about excessive drift to the left. Page 893.

https://www.google.com/books/edition/Th ... frontcover

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butlersrangers
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Re: Deviation and Drift

Post by butlersrangers » Tue Nov 24, 2020 2:55 am

Thanks, Knute.

The article does mention the Danish Krag, but, only in the context of Denmark being a country that adopted a Krag model.

The rifles, with the performance issues cited, were U.S. Krags.
Although bullet 'drift' to the left was mentioned, the main complaint was that the sights were not properly calibrated for range and failed to hold their adjustments. (The sight involved was the 1892 U.S. model).

It would be interesting to find information on the performance of Danish and Norwegian Krags related to deviation and bullet drift.
It would be revealing to compare the 'ballistic behavior' of U.S., Danish, and Norwegian Krag rifles at long range, if similar tests were done by Denmark and Norway in the past.

In addition to using a different rimmed cartridge and style of Loading-Gate, there were other significant aspects of the Danish rifle.
The Danish bolt (like the Norwegian model) was fitted to have the guide-rib in contact with the receiver.

Unlike the U.S. and Norwegian models, the Danish Krag has a 'Barrel-Jacket'. This device likely has an influence on barrel harmonics.
The barrel-jacket screws into a collar surrounding the chamber area. At the muzzle, the barrel is free to slide through a supporting bushing.
The Danish barrel is basically free of contact with the stock and barrel-bands.

madsenshooter
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Re: Deviation and Drift

Post by madsenshooter » Tue Nov 24, 2020 10:51 am

butlersrangers wrote:
Mon Nov 23, 2020 9:28 pm
I wish I could speak and read Norwegian.

I wonder if the Norwegians experienced the same phenomena of the extreme left deviation in their model 1894 Krag rifles?

There is a lot of similarity between the U.S. and Norwegian long rifles.

Some significant differences between rifles:

6.5 X 55 mm rimless Norwegian cartridge vs. .30 U.S.A. rimmed (.30-40).

Norwegian rifle - Bolt fitted, so that the rear of 'guide'-rib was in contact with receiver wall.

Norwegian rifle - A vertical screw anchored the barrel to the stock, just in front of the receiver.
(I wonder if Springfield Armory ever tried this)?
Norwegian Krags have a left hand twist to go with their left hand barrel threads.

FredC
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Re: Deviation and Drift

Post by FredC » Tue Nov 24, 2020 5:07 pm

Steel is elastic and there are so many forces unleashed when you pull the trigger. Rotational force as the bullet engages the rifling, stretch from the pressure, swelling as the bullet goes down the barrel and from the rapidly changing pressure. Think of the barrel as a piano string changing the weight or length changes the frequency if vibrates at. Each barrel length variation, ammo weight, velocity, chamber pressure, stock attachment through the barrel bands, thickness of the barrel, weight of the forward end of the stock, weight of the barrel bands and bayonet lug , and direction of the rifling twist is going to affect the whip. I doubt if I named all the variables that could affect it. There was something that generally repeatable in the rifle and carbines. US rifles the bullet exited during a sideways portion of the whip and the carbines during a rather neutral part of the whip. Still my guess today, pending more info.
Anyone found a good video showing muzzle whip?

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butlersrangers
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Re: Deviation and Drift

Post by butlersrangers » Tue Nov 24, 2020 6:54 pm

'Madsenshooter' brought up a very good point about Norwegian barrels having a Left-Hand Twist.
(If I ever knew this, I had forgotten it: not the L.H. barrel threads, but, the L.H. rifling-twist)!

In theory at least, 'rotational bullet drift' with a Norwegian Krag barrel should be to the left.
If Norwegian Krags exhibit a 'bullet deviation' to the left, as shown by U.S. Krag rifles, the deviation would be in the same direction and simply add to the bullet rotational-drift.
We would not see the odd 'curve ball' effect that was detected in U.S. rifles.

If Norwegian Krag bullets 'Deviated' to the right, upon leaving the rifle bore, then the 'left rotational-drift' might create a 'curve phenomena', similar but opposite, the U.S. Krag experience.

FredC
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Re: Deviation and Drift

Post by FredC » Tue Nov 24, 2020 7:54 pm

You have it now. Deviation and drift are different animals. If they are in the same direction, it would be exaggerated, opposite directions sort of self canceling depending on range. If the deviation were up or down, just compensate with the sight elevation.
Do not know if this guy is on to something or all wet:
https://www.youtube.com/watch?v=FdwN5qlWMVA
It is still hard to believe that most US Krags spit the bullet slightly opposite of the drift if it was only harmonics. With all the variables mentioned earlier.
The experimental Krags with 26 inch barrels may have done something different than the 30 inchers and carbines.

https://www.youtube.com/watch?v=fbuaH6D2Qgc
Most of the visible whip is after the bullet leaves the muzzle. Near the end of this video the messages show how little a barrel has to move to make a minute of an angle deviation.

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