All “low number” bolts have the bolt handle bent straight down, perpendicular to the axis of the bolt body. Generally speaking, “low number” bolts can be distinguished from “high-number” bolts by the angle at which the bolt handle is bent down. The bolts from such rifles were often mixed during rebuilding, and did not necessarily remain with the original receiver.

During WWII, however, the urgent need for rifles resulted in the rebuilding and reissuing of many “low-number” as well as “high-number” Springfields. In view of the safety risk the Ordnance Department withdrew from active service all “low-number” Springfields. Those Springfields made before this change are commonly called “low-number” rifles. All Springfields made after this change are commonly called “high number” rifles. This was commenced at Springfield Armory at approximately serial number 800,000 and at Rock Island Arsenal at exactly serial number 285,507. To solve this problem, the Ordnance Department commenced double heat treatment of receivers and bolts.

It proved impossible to determine, without destructive testing, which receivers and bolts were so affected and therefore potentially dangerous. 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.

1903a1 springfield serial numbers