Just a brief history of the M1 Carbine.
38 months of production (June 1942 to August 1945). 9 major manufacturers and over 1600 subcontractors produced 6,117,827 carbines during this period. At full production some of these major manufactures produced 1400 complete M1 Carbines per DAY!
M1 Carbine Production
Inland Manufacturing Division, G.M.C......2,632,097 43.0%
Winchester Repeating Arms Co..............……818,059 13.5%
Underwood-Elliot-Fisher Co................……..545,616 8.9%
Saginaw Steering Gear Div., G.M.C........…...293,592 4.8%
National Postal Meter Co..................………..413,017 6.7%
Quality Hardware & Machine Co.............…..359,666 5.9%
International Business Machines Corp..…..…346,500 5.7%
Standard Products Co......................………….247,160 4.0%
Rock-Ola Co...............................……………..228,500 3.7%
Saginaw Grand Rapids S'G'..………………………..223,620 3.6%
Irwin-Pedersen Arms Co..…………………….3,542 .05%
I-P had assembled only 3,542 guns at the time, none of which were accepted by the government.
Total: 6,121,369 Carbines Note: Auto Ordnance was subcontracted by I.B.M. to make few M1 Carbine receivers for IBM, few early NPM receivers are marked "Rochester", for the Rochester Defense Corp. A very few late receivers (239) are marked "CCC", for Commercial Controls Corp.
Some Quality Hardware carbines were assembled using receivers made by Union Switch & Signal Co, hence the "UN-QUALITY" marked carbines.
The list goes on.
Both Irwin Pederson and Saginaw S'G' were made at the same plant.
Few Irwin Pederson receivers tested acceptable were used, identified Saginaw S'G' and the remainder scrapped when Saginaw division of GM took over IP in Grand Rapids.
The best book for history of the m1 Carbine is War Baby by Larry Ruth.
All USGI M1 Carbines are equal to each other. All parts interchange between all USGI manufactures.
IAI is hit or miss with reliablity. A decent shooter USGI will run about $450.00 in which you can replace the barrel on to have a equally accurate rifle as a new IAI but it will be USGI.