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There is only one standard for the dimensions, machining, quality, and life span of every part on an M1 Carbine. The standard adopted by U.S. Army Ordnance for the U.S. .30 caliber carbines M1, M1A1, M2, and T3. There is no other standard. Ordnance standards were established based on research and development, testing, field use of the carbines during WWII, and more. These standards insured the parts were interchangeable between all of the U.S. GI carbines, regardless of manufacturer. They also set the requirements each part would have to meet to pass inspection, not only by the manufacturer but also by U.S. Army Ordnance inspectors assigned to the manufacturing facilities of each of the primary contractors making carbines. If a manufacturer didn't get it right, it didn't go out the door on a finished carbine. If a manufacturer consistently and repeatedly didn't get it right they risked losing their contract.
Almost all of the post war commercial carbine manufacturers started out using as many of the surplus GI carbine parts as they could get. As the availability of each part dried up, each commercial manufacturer made, or subcontracted to be made, a commercially manufactured part that would fill the role of it's GI counterpart. While these commercially manufactured parts may have been dimensionally the same as a GI part, none of them were manufactured using the standards established by U.S. Army Ordnance. The new "standard" became whatever "worked" and was cost efficient. How well it worked and for how long was/is nowhere near the quality and lifespan of any of the parts manufactured for U.S. Ordnance. Commercial manufacturers could get by with parts that didn't meet the standards of U.S. Ordnance as their carbines were mostly made for the average citizen during peace time, not soldiers subjecting their carbines to conditions common during a war.
If a commercial carbine and it's parts were manufactured to GI dimensions, then they were "GI compatible", meaning they could be interchanged with all other parts manufactured to GI dimensions, including the surplus GI parts. Most, but not all, commercial carbine manufacturers attempted to stick to these dimensions and interchangeability. Some did it better than others.
Buying a Replacement Part
The first thing you need to determine is if the part you want to replace is "GI compatible". The table below lists the commercial carbine manufacturers and identifies which ones made carbines that have "GI compatible" parts.
If a carbine is indicated as less than 100% "GI compatible", read the web page for that particular manufacturer.
If a carbine and it's parts are GI compatible, the best replacement part is one that was manufactured for U.S. Army Ordnance (surplus GI parts-see bottom of page). There are plenty still available and still in very good condition with many years of service left in them. If the cost is above what you want to pay for a part, the commercially manufactured parts are an option. Realize the quality control standards are an unknown. Most GI compatible parts will work. The questions is, how well and for how long. Most parts will wear out quicker and need to be replaced sooner than their GI equivalent would.
The following parts should be inspected occasionally and replaced before the wear becomes excessive. Parts followed by an asterisk (*) are safety critical parts you should seriously consider replacing with GI surplus parts instead of their commercial equivalents if your carbine's parts are GI compatible. A few commercial companies may have manufactured and hardened them to the high standards necessary for safety. The problem is knowing which commercial manufacture did and how to identify their parts from those who didn't. The markings used by U.S. Ordnance contracted companies for quality control served a purpose. Commercial equivalents rarely have identifiable markings. Testing each part requires equipment and expertise that is cost prohibitive.
Where do I buy the parts I need?
I do not endorse retailers. There are plenty of other retailers, just do an internet search on what you want to buy and shop around. Gunbroker.com is an auction website with hundreds of sellers offering just about any part you would need. Like any other internet auction website, common sense and caution when dealing with people you don't know is advised. On the links page there are links to parts suppliers I have found to be honest and reliable.
A Special Note Regarding Surplus U.S. GI Parts
U.S. Ordnance redesigned a number of parts, several more than once. Most of these changes were to improve reliability and/or function, manufacture time, and/or cost. A few of these changes were important enough to merit replacing the earlier part with the later variant when the carbine could be inspected by U.S. Ordnance personnel. None of these changes were so critical as to merit a massive recall.
One of the unique things about the U.S. GI M1 Carbine is almost all of the parts are backwards and forwards compatible regardless of whatever change was made. The few exceptions aren't realistically an issue when buying replacement parts. The earlier parts tend to be less common and more expensive. The later parts generally tend to be more common and less expensive. A few of the later parts manufactured after WWII are still available in new unissued condition.
Later variants that improve function, reliability, and accuracy include the following:
Barrel Band with bayonet lug, as opposed to bands without the bayonet lug (accuracy) | ||
![]() 1st style Barrel Band | ![]() 2nd style Barrel Band | ![]() 3rd style Barrel Band with bayonet lug |
Slides with angled face above chamber (deflects spent casings away from chamber) | |
![]() Slide w/ flat face | ![]() Slide w/ angled face |
Magazine Catch with the letter M on it's face, or an M2 mag catch (works with both 15 and 30 round magazines-the M has nothing to do with the mfg) | |||
![]() 15 round mag catch | ![]() 15 & 30 round mag catch | ![]() M2 15 & 30 round mag catch | ![]() M2 mag catch arm |
Rotary Safety as opposed to push safety (eliminates pushing the wrong button) | |
![]() Push Safety | ![]() Rotary Safety |
Adjustable Rear Sight, adjusts for windage and elevation (accuracy) | |
![]() Flip Sight | ![]() Adjustable Rear Sight |
Note: GI Round bolts are no better or worse than GI flat bolts on a semi-automatic carbine
Some of these variations are shown on the page devoted to carbine Nomenclature. A basic introduction to the markings found on various surplus GI parts is included on the bottom of the Nomenclature page.
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