When looking at buying an original M1A1 you have to be careful. Please don't rush in, this happened to a friend off mine and without doing some home work it can be very costly.
Firstly and most importantly - ALL M1A1 Carbines are made by Inland Manufacturing Division of General Motors and are marked with 'INLAND'. There are no other manufactures who made the M1A1, no matter who tries to convince you otherwise.
There were two production runs of around 70,00 each. The first started late in 1942 until October 1943 and had all the typical identifiers of early wartime carbines. type 1 barrel bands (no bayonet socket), high wood and flip sights.
The second production run started in April 1944 and finished at the end of the year. This second run has typical later war carbine features like the adjustable sights, low wood and some even had the type 3 barrel bands at the very end of the production run.
INLAND made both M1 and M1A1, there is no way to tell what numbered gun went into what stock. Which means that just because an original deactivated INLAND marked carbine in a folding stock is an original M1A1. It just points you along the right track...
The first production run of the M1A1 Carbine seems to all have 6 digit serial numbers. However ones that have been noted to have been seen and recorded ranges from examples in the:-
100,000s barrels dated Dec 1942
200,000s " " March 1943
300,000s " " " "
400,000s " " June 1943
500,000s " " July 1943
800,000s " " October 1943
The second production run
5,100,000s barrels dated March 1944
5,200,000s " " " " and May 1944
So, things to check. If you get any NO's to these questions then ask yourself if this is genuine or not.
Is it made by INLAND?
Does the serial number fit with the numbers shown above?
If so then the only thing to now check is the M1A1 stock.
All M1A1 stocks are made of Walnut, anything else is wrong. Walnut has lovely grain patterns. If you can't tell one wood from another, get Googling "how to know if wood is walnut"
All the metal on the stock should be parkerized and not blued. Again, if you don't know the difference, get Googling!
The pistol grip will always be marked with proof mark, showing the gun has been test fired. This happens to all guns. It is found on the side of the pistol grip or very back centre stock.
At the bottom of the pistol grip will have OI stamp for Overton Inland who was only manufacturer of this stock. Also, is the crossed cannons emblem, sometimes these can both be a little hard to spot. So look closely, before dismissing.
Butt stock rear plate. These cast pieces all contain the same part number 'B257614' then followed by something that looks like one of the playing pieces from Trivial Pursuit that you put the bits of 'cheese' into. After that 'logo' there is the number of the cast which seems to range between 3 to 12.
The leather piece on the stock is very commonly missing, but if present it should be of a nice high quality leather and always very very dark brown in colour. The rivets that hold this in place and dull, never shiny and unmarked*. (* with exception to a few rebuilds where brake rivets were used and these can be marked 7/4.
If you've gotten this far with no problems and everything has checked out then there is one last thing to check. Carefully take the Carbine out the stock and inside the barrel channel it will be stamped IO. If its also there, then you either have a very impressively worked fake, or its an original.