http://www.odcmp.com/Sales/m1903.htm
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.
Generally speaking, “low number” bolts can be distinguished from “high-number” bolts by the angle at which the bolt handle is bent down. All “low number” bolts have the bolt handle bent straight down, perpendicular to the axis of the bolt body. High number bolts have “swept-back” (or slightly rearward curved) bolt handles.
A few straight-bent bolts are of the double heat-treat type, but these are not easily identified, and until positively proved otherwise ANY straight-bent bolt should be assumed to be “low number”. All original swept-back bolts are definitely “high number”. In addition, any bolt marked “N.S.” (for nickel steel) can be safely regarded as “high number” if obtained directly from CMP (beware of re-marked fakes).
CMP DOES NOT RECOMMEND FIRING ANY SPRINGFIELD RIFLE WITH A ”LOW NUMBER” RECEIVER. Such rifles should be regarded as collector’s items, not “shooters”.
CMP ALSO DOES NOT RECOMMEND FIRING ANY SPRINGFIELD RIFLE, REGARDLESS OF SERIAL NUMBER, WITH A SINGLE HEAT-TREATed “LOW NUMBER” BOLT. SUCH BOLTS, WHILE HISTORICALLY CORRECT FOR DISPLAY WITH A RIFLE OF WWI OR EARLIER VINTAGE, MAY BE DANGEROUS TO USE FOR SHOOTING.
THE UNITED STATES ARMY GENERALLY DID NOT SERIALIZE BOLTS. DO NOT RELY ON ANY SERIAL NUMBER APPEARING ON A BOLT TO DETERMINE WHETHER SUCH BOLT IS “HIGH NUMBER” OR “LOW NUMBER”.
