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Krag Accuracy and Bullet Drift "back in the day"

Posted: Thu Oct 15, 2020 7:25 am
by butlersrangers
A couple of pages from the 1917 Ordnance Manual, indicating anticipated accuracy and strange pattern of 'bullet drift' experienced with the (Krag) U.S. Magazine Rifle.

With improved Propellants and Bullet construction, it seems likely that the 1.2 inch "radius of circle of shots" @100 yards, (2.4 inch groups), is being improved upon by many of today's Shooters.

Re: Krag Accuracy and Bullet Drift "back in the day"

Posted: Sun Oct 18, 2020 6:48 pm
by Old Soldier
So if the radius of the shot group is 1.2", is that not what we would call a 2.4" group? That matches my experience 2.5-3" groups at 100 yards.

How does the rifle drifting LEFT match your experience? Anyone have an explanation as to how a rifle with right hand twist could drift left?

Re: Krag Accuracy and Bullet Drift "back in the day"

Posted: Sun Oct 18, 2020 9:26 pm
by butlersrangers
Old Soldier - The phenomena of the bullet movement to the left was discovered by extensive trial firing experiments by the Ordnance Department in the late 1890's and early 1900's. It was duly reported in the Appendix of period Annual Reports.

It was a concern, especially since, they were trying to calibrate range increments and drift compensation on new sight models.

IIRC - The eventual conclusion was that bullets exited the Krag bore 'inclined' to the left, probably due to vibrations of the barreled/action, influenced by the asymmetrical lock-up of a single locking-lug.

This bullet deviation increased with range and 'maxed out' at about 700 yards. Eventually, the rotational 'Bullet Drift', (which had been continuously going on), caused the bullet to 'comeback' and cross the line of sight at around 1,100 yards. After 1,100 yards the bullet continued the right drift. (This is all shown in the manual's tables).

The 22 inch carbine barrel and 26 inch Board of Ordnance & Fortifications rifle barrel did not show the same extreme behavior as the 30 inch rifle barrel. (Their sights had no drift compensation).

A mystery to me is the 'built-in drift compensation' used on the model 1901 rifle rear-sight, given the known ("Banana Curve") horizontal bullet movement to the left, back to the center, and thence to the right.

It would seem logical, if the 1901 rifle sight-leaf had moved the slide more in a curved pattern, to the right to 700 yards and then slowly back to the left.
The steady angled incline to the left, that was actually used on the 1901 rifle-leaf, appears to just exacerbate the sighting error with the initial bullet movement to the left.

FWIW - I have never shot targets at over 200 yards with a Krag, so none of these factors have been noticeably experienced.

Re: Krag Accuracy and Bullet Drift "back in the day"

Posted: Mon Oct 19, 2020 4:42 am
by Old Soldier
Thank you. I did not doubt their findings, as they really had their ducks in order, but I would have never come up with the answer.