I read with interest the post concerning the Danish 6.5x55 (intended for for Swedish 1896 rifles used by the Danish Army) that was condemned because the bullets left cupronickle deposits in rifle barrels.  This was supposed to increase pressures as more & more of the stuff was fired, as would be likely if military ammo was used as such.

In one of Phil Sharpe's monumental works, he wrote about shooting a 1903 Springfield at Camp Perry (early on, between the wars).  He detailed how his quite accurate National Match rifle suddenly became wildly inaccurate, which he blamed on cupronickle-jacketed bullets.  These were 150-grain bullets, issued before the 172-grain M1 match ammo was loaded.  Sharpe blamed the fouling on the high velocity (2700 fps?) ammo and said that at lower velocities, cupronickle fouling was not a problem.  IIRC, he made reference to issue Krag ammo not fouling.

I always thought that the pre-WW1 issue Krag bullets were cupronickle.  Is that correct? 

And was cupronickle fouling a problem with the Krag?

And would the bullets salvaged from the Danish ammunition be OK to use in a Norwegian Krag if you kept the velocity levels at about 1800 fps?

As far as I know, all early Krag issued ammo used a cupro-nickel bullet.  I have a box of FA from 1907 and WRA from the teens and both are cupro-nickel.  I don't remember reading anything about excessive fouling in Krags.  Of course, cleaning would have been vital since the primers used were highly corrosive, and maybe that played into reducing the Cupro-nickel fouling.

I seem to recall reading in Hatcher's notebook that the cupronickel was ok at Krag velocities, but not at 30-03 velocities.  Must've really got bad at 150gr velocities. Seem to recall, means I think that's where I read it.

I shot up a bunch of old cupro-nickel jacketed bullets in a Springfield one time long ago. I experienced severe jacket fouling. Following the old timer's protocol for removing it, I filled the bore with stronger ammonia (the Real McCoy) and let it sit for a while. When I un-stoppered the barrel and dumped it out I got a good whiff of the ammonia fumes and passed out. My wife dragged me away and I revived ok. Lesson learned: don't pull that trick in the bathroom, and wear a respirator. :D

Oh, it did a swell job of removing the cupro-nickel fouling. (I did start passing up on the cheap WWI surplus '06 ammo at the gun shows after that.)

Cupronickel jacketing became a problem when velocities exceeded 2100 fps or so. Read some of Townsend Whelen's old articles on this. This was a major problem for the 1903 up until right after WW1. Ordnance figured out that adding a small amount of tin to the jacket alloy solved the metal fouling issue. The Germans had apparently stumbled on the same solution - perhaps never had the problem - as they had tin mixed in their priming compound from the earliest adoption of the 8mm Mauser.