Who made the sears and roebuck slug model 446.511761 12 gauge?

It is a Mossberg 500. However, parts only interchange with a model 500 from the same serial sequence, i.e. if you have a G, H, or J serial number, it will only interchange with an older G, H, or J serial number.

Source: National Mossberg Collector's Association at www.havlinsales.com