Odd 03 Bbl.
Here awhile back I posted a thread about a friends 03 Barrel, it had a slot machined into the muzzel end that was perpendicular to the bore. John B. replied(if I remember correctly) plus a few others that it was probabley done after issue by someone for a specific purpose. Well there are 2 of them on Gunbroker that are identical to the one my friend has. I would love to have somebody look at them and comment(John espeicially) They are at the bottom of the page listed as "1903 Springfield barrel".
Every 1903 barrel has these. It's where the pin goes through to keep the front sight base sleeve from slipping off the barrel.