The U.S. Caliber .30 Carbines - Parts

The U.S. Carbine Caliber .30

Trigger Housing Group






Trigger Housing

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    Trigger Spring
    Trigger Pin
    Sear Spring


The design of the trigger initially approved for use with the M1 Carbine was altered slightly when it was found the sear occasionally remained in the rear position when the trigger was released. This required disassembly of the carbine to release the sear so the carbine would function. Carbine production using the early trigger (Type I) had already started at Inland, Winchester, Underwood, Rock-Ola and Quality Hardware when the problem was discovered and the design was changed. The angle of the front of the pedestal supporting the rear of the sear was increased producing the trigger used throughout the majority of production (Type II). U.S. Ordnance made the change retroactive by ordering all earlier triggers modified to the later design, though some survived as the carbines they were on were already in service.

Type IType II

Recognizing the difference in the two designs is very difficult. Other authors have suggested measuring the distance from the face of the pedestal to the center of the trigger pin hole. I've found the easiest method is to repeatedly compare the pedestal on the left (above) to the one on the right. Repeated visual comparison of the two trains the brain to spot the difference when it's encountered elsewhere. Note also the difference in the machining of the slot behind the pedestal that engages the trigger spring. If you locate a trigger with the earlier design it should be set aside as collectible and replaced if you intend to fire the carbine.

The Type II Trigger used throughout the majority of production

Top View

Front View

Tooling Variation

Triggers produced at Irwin-Pedersen and Saginaw Gear at the Grand Rapids (S'G') facility may have one or two
characteristics specific to the triggers manufactured on some of the tooling at this facility.

Assembly Tip

Assembling the trigger, sear and sear spring into the trigger housing can be a challenge when exerting rearward pressure
on the sear and sear spring while attempting to align the holes and insert the trigger pin that secures them. There are
several different methods of simplifying this task including the one shown below.

Shorten a spare trigger pin to the width of the hole in the trigger. Assemble the trigger, sear
and sear spring together as a unit with the shortened pin. Place the assembled unit inside the trigger housing and
align the hole in the trigger housing with the shortened pin. Push out the shortened pin with the full size trigger pin.

Trigger Spring

The Trigger Spring manufactured throughout the majority of production is shown below as the Type II. The Type III Trigger Spring was a variation
manufactured by National Postal Meter. The Type I Trigger spring was absent the loop and reportedly used by Inland and Winchester during
very early production.

Type IType IIType III

Assembly Tool

During WWII an L shaped tool was developed to assist in compressing the ends of the trigger spring to insert it into the trigger housing.
The spring is pushed into the open end of the tool then inserted into the hole in the rear of the trigger housing. The tool below is
larger than the original and manufactured post WWII.

The front of the spring engages the slot behind the trigger pedestal
providing downward tension on the rear of the trigger.

Trigger Pin

.6" long and .125" in diameter, Trigger Pins were blued


 Type I 

This sear was used from the beginning of production. The single most recognizable characteristic
is the absence of a hole through the rear half of the sear above the sear spring.

By the second half of 1943 the design was slightly changed in an effort to improve trigger pull. The changes are
almost imperceptible and most type I sears have had the changes made.

The nose of the sear (left) was ground to give it a small radius at the point it engages the rear of the hammer (right).

The lower edge of the rear of the sear (left) was ground at a slight angle (right).

This design change was mandated for all existing sears. Those already shipped as part of a carbine were to be altered
by Ordnance field personnel whenever the opportunity presented itself. Those altered were to be identified as such
by placement of a grind mark on top of the rear of the sear.

The majority of Type I sears have been modified to include these changes and more often than not do not include the grind mark.
Post WWII Ordnance refurbishment operations mandated this change on the earlier sears without requiring the grind mark. By 1953
the absence of the grind mark was no longer reliable in determining if the alteration had been done.
(Ordnance Manual "TM 9-1276, Cal. .30 Carbines M1, M1A1, M2, M3", February 1953).

These changes were incorporated into the manufacture of new sears producing the "Type II" sear.

 Type II 

The single most recognizable characteristic is the hole through the rear half of the sear
above the sear spring.

 Type III 

Sears designed for use with the Model M2 Carbine included an elevated platform on the front half of the sear on which the Disconnector rested. Changing the Selector Switch
to automatic fire caused the Disconnector to push the sear downward below the hammer as the trigger was held to the rear enabling automatic fire.

The M2 sear, while mandatory for automatic fire, was also used on semi-auto only carbines as an alternative to the earlier sears.

Machining Variation

Sears manufactured by Springfield Armory were absent the typical SA marking.
They can be identified by a slight elevated ridge toward the front of the sear.
M2 Sear manufactured
Rock Island Arsenal
M2 Sear manufactured
Springfield Armory

Sear Springs


The Sear Spring used at the beginning of production had a diameter of .145" with 16 coils .7" in overall length. To improve trigger pull it was reduced to
15 coils .655" in overall length with the coils at either end tapered smaller. Most early sears were replaced with the later sears at some point.

Should you have questions, assistance is available on our Discussion Forum.

The Discussion Forum also serves as a reference desk for the more advanced material that could easily overwhelm a website and is often subject to opinions that may vary
due to a lack of original documentation. A number of researchers and authors are present on the forums, helping others and seeking information for various research projects.

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