*WARNING ON “LOW-NUMBER” SPRINGFIELDS
M1903 rifles made before February 1918 utilized receivers and bolts which were single heat-treated by a method that rendered some of them brittle and liable to fracture when fired, exposing the shooter to a risk of serious injury. It proved impossible to determine, without destructive testing, which receivers and bolts were so affected and therefore potentially dangerous.
To solve this problem, the Ordnance Department commenced double heat treatment of receivers and bolts. This was commenced at Springfield Armory at approximately serial number 800,000, and at Rock Island Arsenal at exactly serial number 285,507. All Springfields made after this change are commonly called “high number” rifles. Those Springfields made before this change are commonly called “low-number” rifles.
In view of the safety risk the Ordnance Department withdrew from active service all “low-number” Springfields. During WWII, however, the urgent need for rifles resulted in the rebuilding and reissuing of many “low-number” as well as “high-number” Springfields. The bolts from such rifles were often mixed during rebuilding, and did not necessarily remain with the original receiver.
CMP DOES NOT RECOMMEND FIRING ANY SPRINGFIELD RIFLE WITH A ”LOW NUMBER” RECEIVER. Such rifles should be regarded as collector’s items, not “shooters”.
http://www.thecmp.org/Sales/rifles.htm