Bsa,
I have used a bunch of different decoppering powders in the past few years, my experience is they don't leave as much powder fouling as many other powders, especially with close-to-maximum loads. But that's pretty common, except with older-style spherical powders.
In fact they've work so well than during some of my recent "load test" articles I deliberately alternated handloads with decoppering powders with "standard" powders--and checked the bore with my Gradient Lens bore-scope after each range session. Never found more than a faint trace of copper--partly because decoppering powders will indeed remove copper left after firing standard powders.
One of these tests involved around 150 rounds in a Mauser M18 7mm Remington Magnum. I never cleaned it throughout the tests, and it was still grouping great, with very little coppering. In fact, I have generally come to the conclusion that using decoppering powders will will "break in" new barrels (like the one in the M18) without the tiresome process of frequent cleaning. This is because they leave so little fouling that the bullets are pretty much running through a clean bore, allowing bullets to smooth the bore.
Of course, the other factor is that so many of today's factory barrels are very smooth, even in inexpensive rifles.
