Interesting. Not sure fouling was a huge problem with Enfields using US/CS ammunition either. I have not read elsewhere that it was. Earl Hess notes in "Kennesaw Mountain" (p 132) that Sam Watkins claims he fired 120 rounds (I believe his company was issued the P53 Enfield) and the problem he noted was not fouling but rather the barrel getting too hot to hold. I think Watkins also mentions this in memoirs, "Company Aytch." Or perhaps Sam Watkins company was issued English Enfield ammuntion, but this is not mentioned and I don't believe we should automatically infer that was the case.
Are there any period sources that mention the P53 Enfield fouling rapidly with US/CS cartridges? The author of this otherwise fine article mentions it as though it was defacto. I'm not sure that was the case...