The fouling problem doesn't surprise me. It gave trouble with all attempts to make 8mm. rifles work with a larger charge and faster twist than the common black powder rounds. The largest powder grains you can get would probably foul less. The British probably got the best results in this type of project with a solid pellet of compressed black powder in the .303 Lee-Metford. I believe it was pierced up the middle, and probably originated in the technology developed for the Congreve rockets. That had been tried and found insufficiently accurate in the .577 Snider, but higher pressure might have made some difference.
I have loaded, many years ago, for the single-shot Guedes. The 8x60R it used is virtually identical to the 8x56R, and I don't know whether the chamber neck was shortened to prevent interchangeability. My groove diameter was a fraction under .331in., giving unusually deep grooves which were quite unnecessary and must have worsened the fouling problem considerably. It was designed around the idea of patching the bullet with copper foil, which was dropped because of irregularity in its detachment from the bullet.
I was impressed by my 245gr. gas-check mould in .330 diameter, from NEI. But that was before NEI went through a bad patch on the death of its founder. The business is currently inactive and for sale, and we must hope for improvement, since I believe most of its mould cutters are those Walt made. I also used Speer 275gr. .338 semi-pointed softpoints, which my Rockchucker press easily sized down .338 jacketed bullets with a simple ring die. They came out a thousandth larger than lead, so it is true that a jacket springs back from sizing, and the core presumably doesn't. With their long unsized nose, it is unlikely that the core wound up anywhere near that theoretically possible .0005in. off-centre. Anyway, there is no need to do this, as a cast gas-check bullet works well at Guedes velocities.
It was at a bad time for black powder supplies in the UK, and what I could get gave velocities of only about 1200ft./sec. The bullets frequently tumbled, for a bullet keeps its rotational velocity much better than its linear motion. This means they were less well stabilised than a bullet which has slowed to 1200ft./sec. at long range. I never tried Pyrodex, but I began with 24gr. of Reloder 7, giving about 1525 ft./sec. with the NEI bullet, at which it penetrated two feet of end-grain larch timber. So we have a better big-game cartridge than it sounds, ample for anything that is unlikely to eat you up or squash you flat. Approximately factory ballistics of1710 ft/.sec. and good stability were obtained with 30gr. of Reloder 7, producing very reassuring pressure indications, but I would not go over 28gr. with my sized-down Speer 275gr. semi-spitzers. These gave greater though not alarming primer deformation, probably due to friction and dimensions rather than weight.
I have seen a velocity of 2000ft./sec. quoted for the late Portuguese Kropatschek, but I don't know what bullet weight. I am sure this could be done safely, and wouid make it a very effective round. What's wrong with a high velocity .33 Winchester, which is very similar?
I have been shown a picture of a cartridge found illicitly with a metal detector in the Boer trenches at Colenso, from 1899. The bullet, too corroded to measure accurately, appeared to be of thin nickel rolled on steel, and the case was the shorter 5mm. length. Such a bullet would surely have worked very badly in the Guedes, and I don't believe the Boers had any Kropatscheks.
I have some 8x60R Kropatschek blanks, with headstamps from the late 1880s to about 1904. They have case lengths of about 56 to 60mm., probably just as they came from the drawing process, and not the common practice of the time, of making blanks from used bulleted rounds. They were loaded with very finely grained smokeless or semi-smokeless, a cotton wool filler and a hollow wooden bullet.I hoped to reload them, and the main reason I didn't was that many of them had split necks, even without insertion of a tight-fitting bullet. Very possibly they had been rejected for orthodox loading for this reason. They were also balloon headed and surely corrosive, so they didn't seem worth trying.
It is very unlikely that smokeless powder played any part in the design of the 1886 Kropatschek. It is very similar to Kropatscheks of the 1870s, when it couldn't possibly. The French invented smokeless rifle powder in 1885, and for some years French soldiers were threatened with ten years in jail for opening a cartridge - which being an anarchic breed, all of them probably did. The British had the French "chemical powder" very much in mind in deciding that the new Lee-Metford had to be a .303, but were just guessing when they made the sight graduations for a slightly higher velocity than black powder would give. Austria-Hungary, who made the Kropatschek, and Portugal, most unlikely to be of any help in the war France knew they had to consider, were probably even further from getting their hands on any. The Austro-Hungarians themselves had to replace the 1886 and 1888 Mannlichers, with their tilting-block locked straight-pull bolts, with the helical bolt-head 1895. They would hardly have got themselves into that expensive mess if they had known about smokeless in 1886.