Re: White deposits in barrel ?
It's a .270 and I've benn shooting factory 130 gr. Hornady SST's.
I swabbed it with a couple of patches wet with Hoppe's this weekend and stood it muzzle down over a piece of white plastic. This morning, there was some bluish leakage from the barrel, so I'm now guessing it was probably, like you said, some corroding copper fouling from where I'd swabbed it at the range.
Once I receive my cleaning stuff I'll give it a good scrubbing to get the rest of the copper out.