You probably have seen my post just a few days ago and obviously I am new at this also but I have been very busy at it the last few days and have learned a lot. First off the problem I was asking about seems to be rare and was just a case of my rotten luck for having chosen such a difficult metal to work with for my first attempt, I have been working on the barrel and other parts the last couple of days and it's going really well, much easier than I thought it would to do a professional looking job. My problem turned out to be the material I chose for making the receiver and it's highly unlikely that you would run into that. On these latest parts I too had those streaks you mention and with subsequent rust sessions they will go away, the first couple of applications were disappointing to me but it shouldn't have been, after the third or fourth application the disappointment turned into delight as the parts started looking really good! Just keep at it and you are going to be really pleased as the work progresses, I certainly was and I had no prior experience either.
BTW, I just gave up on the heat treated 4140 and sent it to a gunsmith for hot blue, even that it turns out is tricky with that particular metal and it will turn out a purplish color when hot blued unless it's done properly.