Yes, I agree with broom; nothing I recognize, so a chamber cast would be useful, but only if wanting to retain the barrel. If viewing the rifle as a 'donor' action, to be rebarreled, make sure everything else is in order and buy appropriately for a rebarrel cost.
I would think the initials are from the gunsmith (s).
The 250ND is .250" Neck Dia which means depending on cases you may or may not have to turn or clean up the necks since a loaded neck dia would be .248".
The sellar of that rifle should be furnishing you with all the information on that chamber along with loaded,fired cases. If your not set up for neck turning that could be an added cost plus the bushing type dies.
Here is a gunsmith site and look at his chamber reamers http://www.bryantcustom.com/services/availabl.htm you see his has 3 reamers with different neck dia from .246",248" and .250" for the 223 that are listed as match/tight neck reamers then he list standard reamers that don't require neck tunrning.
I turn neck for some of my tight neck rifles etc so for me it be no big deal to me. Only thing I'd be alittle concern about is the initials that close to the receiver barrel may of been set back and rechambered which is pretty common that type chamber.
this is just me but you should be buying a rifle like that from the owner and he have the history on that rifle. If not be a gamble on accuracy and you want someone to bore scope that rifle, me I'd pass unless I could buy it for the action/stock as a rebarrel project.
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