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Other than the visible external metal/wood conditions, there are only two other mandatory checks to make before buying a tube-magazine Ruger .44 Auto Carbine.
The 1st is to look at the latch located at the rear of the loading gate on the bottom of the action - since that latch is usually depressed by the cartridge nose when loading the magazine, little or no (blued) finish wear indicates that it wasn't loaded/shot very much.
(AND, if unworn, will expand exponentially the chances of check #2 below having a positive result)
The 2nd , and more important (go/no-go), thing to check is the status of the interface which holds the forward end of the trigger guard housing to the bottom of the receiver.
The interface is the lug on the aluminum TG housing, which will eventually crack and/or break off, allowing the front of the TG housing (which contains the cartridge feed mechanism) to "float", causing jams that change an auto-loading rifle into a single-shot.
The status of the lug can be checked w/o dis-assembling the rifle via placing the butt on one's hip, with one hand holding the stock & the barrel securely, so any movement can be readily felt while the other had tries to move the front of the TG housing up/down.
To try to move the TG housing up/down, the hand that's not holding the barrrel/stock should have the thumb (or one finger) inserted up past the loading gate, into the rear of the magazine opening, with the other finger(s) are against the bottom/outside of the forward part of the housing.
The digit inside the magazine throat pulls "down" on the housing, and the outside digit(s) push "up", in alternate movements, sensing if there is movement of the front of the housing, relative to the receiver/stock.
ANY movement should be a deal-breaker, as the housing in an in-repairable item, also made of un-obtainium.
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