How exactly is the warning worded? It may just be that (because JHPs are normally lighter than FMJs) they found that the suppressor wasn't as effective when used with JHPs.
Sorry fellas I just realized that I typed manual I meant website.
I came across it the other day when I was surfing around. Said simply: "JHP's are not recommended for HK suppressors." And for the life of me I can't seem to figure out why?