mongooz
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Although supplies have gotten better, you pretty much load whatever powder you can get your hands on these days. I'm stocked up pretty well with titegroup right now, and autocomp. I like titegroup as it takes very little powder and measures very consistently.
i used to get all my stuff from Lock, Stock and Barrel and Brownell's. and a local shop that's been very well stocked for a long time.
the former (deceased now) owner, built several rifles with me. i engineered them and he built them to spec. he used to put me in front of a LOT of customers because my designs were things that he was very interested in. the last one was a 6mm x 284. it was an absolute nailer.
anyway....they always had lots of supplies on the shelves. however, i haven't been in the game for a decade or so.