Not sure about “rare” as anyone could have one built but here goes: Back in the late 1980’s I was checking the racks at Great Northern Guns in Anchorage, AK. Found a left hand 450 Ackley built on a Rem 700 action by Brown Precision and was wearing a BP stock. It was light and most likely weighed in around 6.5 pounds. Rifle looked unfired. Memory tells me I paid just under $600 for it. Bought some die’s and formed some brass and headed to the range. First shot about knocked my teeth out and bruised my shoulder and jaw. Didn’t have to worry about a second shot as rifle wouldn’t feed anything. It was apparent whoever built it at BP never did a function test. Mailed it back to BP and they fixed it and I had them add a brake. It helped, but not enough. Sold it soon after and glad I did.
My biggest fear is when I die my wife will sell my guns for what I told her they cost.
