What in the world did I get myself into?

[garyc]

Sounds like the barrel is a replacement possibly done during WWII but could have been added later since you can still find WWII Remington replacement barrels with WWII dates for the 03a3 and these would fit an 03 receiver.

Some low numbered 03's were rebuilt during WWII as an expedient to get rifles in the hands of the troops for training and also for use by second line troops like guards and MP's. You can find them with barrels from different manufacturers Remington being one but also a few others that just made replacment barrels. At the beginning of the war there werent enough M1s to go around so they tried to send those to the front line units. Although the Marines used 03's during the Guadalcanal campaign.

The issue with shooting low numberd 03s is that they found that the heat treat methods used on the low numbered ones were inconsistent and that there were a few cases of the receivers blowing up due to bad heat treating. They changed the heat treat method starting with the "high numbered" rifles but once they issued the low numbered rifles they had no way to tell which ones were good or bad.
They did indeed use some low numbered rifles during WWII and those were probably re-heat treated and then had new barrels installed as part of the rebuild. The problem is that there is no way (short of metallurigcal testing which would likely cost more than the rifle is worth) of telling whether the receiver has been properly re-heat treated as part of a rebuild or if someone just replaced tha barrel on an old original receiver. Having said that there were actually very few recorded blown receivers but since there were some the CMP recommends you dont shoot the low numbered receivers as a safety precaution.

Gary C