I remember an article on the early ones in the american rifleman about 2 or 3 months ago. I can't remember the number they said may be in the range , but I do think it was somewhere in the LOW 300 xxx range.
I went ahead and looked it up , seems like the number depends on the manufacturer. Following is a copy of the article mentioned on the net , not the rifleman. And the link to the whole article , a very good read with lots of history and information in it
article.www.snipercountry.com/Articles/SpringfieldM1903
Prior to 1918, there had been scattered reports of burst '03 receivers. A lengthy investigation into the incidents revealed that the forging of '03 receivers at both Springfield and Rock Island was being accomplished more as an art than a science. Those forging the billets of steel into receivers relied upon "eyeballing" the color of the billet prior to finishing. It turned out that under certain lighting conditions (cloudy days, etc.) there were definite differences depending on one's "eyeball", resulting in an occasional "brittle" receiver. Most were perfect, but a few of those that slipped by were suspect... unfortunately there was no metallurgical way of detecting the faulty receivers without destroying them and no way of correcting the brittle metal even if the receivers could have been identified. The metallurgical process was changed and the new receivers were said to be "double heat treated". The new process was begun at receiver serial number 800,001 at Springfield Armory (Feb.1918) and serial number 285,507 (May 1918) at Rock Island Arsenal. All receivers of these numbers or higher are known as "high numbered Springfields" and are considered to be above suspicion. Numbers below those listed are best fired with factory loads or better yet used as collector's items. General Julian Hatcher, then a young ordnance officer suggested drilling a hole in the left side of the receiver as a gas relief port to cut the incidence of burst receivers. While this was generally ignored by the Army, the Marine Corps took the suggestion to heart and many of the Marine Corps low numbered '03s of the era will be found with the so called "Hatcher Hole" in the left side of the receiver. After W.W.I, the Marines solved the "low number gun problem" by rebarreling them when sent back for refit, drilling the Hatcher Hole and reissuing them with instructions that they were not to be used for firing rifle grenades. The high numbered guns are extremely strong and never experienced any problems.
