Re: 600y gun
600 yards is not a real test to a quality built rifle. While you will NEVER go wrong with a quality custom receiver, I would not say it is needed in any way for this type of shooting or this range of shooting.
A Rem 700 accurized properly will make 600 yard shots a breeze as will many other factory receivers if machined properly.
Again, there is no fault in using a custom receiver, just do not think this is the only way to get consistant hits at 600 yards. That simply is not the trueth.
Personally, if I were building a rifle for myself to cover your exact needs, I would look at something in the 6mm to 6.5mm class of bore and as far as case capacity I would start at the 6 BR or 6-250 in the 6mm and probably start at the 260 Rem in the 6.5mm.
There is really no need to get a big case capacity with this range limit in mind. As such, on the top end I would limit the 6mm to a 243 AI case capacity or less and the 6.5mm to the 284 case capacity or less.
Both would have fast twists, both would shoot the VLD or ULD bullets and I would load them to the 2800 to 3000 fps range for best performance with this type of match bullets.
Rifle weight would be a personal choice, me I would like a 12 lb rifle or so. Still packable but plenty stable for 600 yard shots, which still is a good poke out there!!
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