Welcome.
SN is a lot easier to read with X not - and the more numbers the easier. Picture helps a lot.
That said, there were some after market 1903 receivers that were made as cast and are dangerous.
You will see SNs changed to accommodate it inside a known range and struck with Remington.
I am not in depth familiar with the details nor if someone has faked a SC though my recall it was REMS. I have seen a couple of pictures that were faked and it stands out.
Otherwise the receivers are over 5,000,000 and are not stamped with SC or REM.
Sans pictures and good detailed ones my guess is you have a real SC.