The U.S. Carbine Caliber .30
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With the short time span in which the U.S. Carbines were developed and started production, inevitably their use in the field would reveal the need for changes or modifications to the existing design. Additionally, the Ordnance Department and/or one of the prime contractors and/or subcontractors found ways to improve performance, decrease weight, decrease production time, conserve metals, or decrease production costs. To the credit of the original design, none of these changes were mandatory replacements, or mandatory upgrades for the prime contractors when assembling carbines during the war. Not until after the war did the Ordnance Department indicate a number of mandated modifications and parts for the carbines, for the post war overhauls. For a list of these post war modifications and parts refer to the page on Post WWII Ordnance Operations.
Due to the standards set by the Ordnance Dept. all part variations were forward and backward compatible with the U.S. Carbines regardless of who manufactured them or when.
Generally when a new variation of a part was approved by the Ordnance Dept., it was manufactured and became available for the assembly process within a matter of weeks or a couple months. When contractors received these new variations they were added in with the existing variations with both variations being used until the inventory of the previous variation was used up. As such, the later variation wasn't a "replacement" part in the sense of replacing parts as it was an improvement to the prior design.
Just because a newer version of a part was approved by the Ordnance Dept. does not mean every manufacturer assembling carbines used them. One example was the stamped and brazed trigger housing, none of which have been found with the markings of Inland or their subcontractors.
While all changes to parts required approval of the Ordnance Department, it is not unusual to find minor variations specific to a manufacture or subcontractor due to a difference in machines, machining, and/or procedures used by a particular manufacturer. One example would be the small notch on the rear of the triggers manufactured by Saginaw Steering Gear in Grand Rapids, MI.
There were five basic variations of the slides manufactured for the U.S. Carbines, with a sixth likely due to a difference in manufacturing based on who manufactured them as opposed to an Ordnance Dept. approved change.
During production of this variation the decision was made to increase the distance the slide traveled rearward before unlocking the bolt, to improve ejection and reduce flash at the breech. Approximately .040" was removed from the inside of the rear of the slide, where it abuts the gas piston. The opening of the cam cut for the right bolt lug was moved .040" farther forward (see pic below).
To aid in the recognition of the earlier type V from the later type V the Ordnance drawing number/stock number 7160091 was added to the outside bottom of the later design.
The type I slide was cut flat inside the cam that engages the right bolt lug (top).
Type II and later slides have a V shaped cut (bottom).
On November 18, 1943 Ordnance adopted several changes to the type V slide to increase the distance
the slide traveled rearward before unlocking the bolt, to improve ejection and reduce flash at the
breech. Approximately .040" was removed from the inside of the rear of the slide, where it abuts the
gas piston (above).
Positioning the slide .040" farther forward necessitated a .040" increase in the cam cut for the right bolt lug (below).
The changes in the type V slide corresponded to changes in the bolt design adopted by Ordnance the same date. (refer to page on Bolts)
To facilitate identification of the modified type V slides the Ordnance
drawing/part number 7160091 was added to the bottom of the slide.
The type VI M2 slide has Ordnance drawing/part number 7161843 on the bottom of the slide.
The SA on this slide identified the manufacturer as Springfield Armory.
Two types of slide stops and their associated spring were used. The slide stop & spring (left) was eventually superseded by the slide stop & spring (right).
Slide recoil springs were the same throughout production, with 120 coils .258" in diameter with an overall length of approximately 10 1/4".
Specifications for the Recoil Spring Guide indicated it should be
4.90" in length. While three basic variations have been observed,
the differences were the decision by some manufacturers to sharpen
one end or the other which altered the length slightly.
Some spring guides were sharpened on one end or the other by soldiers
to facilitate better use of the spring guide as a tool for carbine
disassembly and reassembly.
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