Fox,
I assume you mean that the action is stamped w/ a serial number but the bolt does not have the matching # electro pencil engraved on it?
If so it could be a simple as someone has polished the bolt body & removed the serial # or it could be a replaced or mismatched bolt. I would want to check the headspace & feeding function on that rifle before buying it.
As far as shooting the .220 Swift, I have owned 3 pre 64 model 70 Swifts over the years & they are "the bomb" for a varmint rifle as far as I'm concerned. All shot very well & one was exceptionally accurate.
Brass is available & they are easy to load for with the exception that the cases tend to stretch & require frequent trimming. I always had the best accuracy w/ 50 or 52 grain bullets but that was 35 years ago & bullets have improved a lot. The Swift in the Pre 64 M 70 rifles has a 1 in 14" twist so I would not try any bullets over 55 grains (I tried some Nosler 60 grain bullets back in the day & couldn't get them to shoot as well as the lighter bullets).
FWIW, I don't think barrel throat erosion or barrel cleaning frequency is any worse than a 22-250 Remington.
