Introduction: HOW TO FILL OUT a CARBINE CLUB DATA SHEET FOR AN M1 CARBINE

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About: I'm a police officer in Michigan and enjoy home improvement projects, and working on machines...any machine, from wristwatches to guns to cars to cameras. I like any outdoor sports, especially scuba diving, a…

Anyone who's ever attempted to fill out a Carbine Club Data Sheet knows how intimidating the process can be, especially if it's your first time.  Since I was unable to find a "How To" guide when I first started doing these sheets, I figured I'd make one.  Hopefully, this will save someone the frustration and confusion that I felt when I did my first few.  I have attached a .jpg file on this page of a Data Sheet, but a much better copy can be had directly from the source:

http://www.carbineclub.com/DataSheetrev31-1-11.pdf

If you're not already a member, I would highly recommend joining the Carbine Club, it's a great source of information for anyone interested in the M1 Carbine and its variants.

If this is the first time doing this, plan on it taking about an hour.  You'll need a clean work area, a few small tools:

1.  a flat bladed screwdriver (for the recoil plate and barrel band)
2.  a punch (for the various pins).  If you don't have a punch, most of the pins will come out either by hand or lightly persuaded with something pointed, like the tip of a pen/pencil small nail, or paperclip.
3.  If you're planning on disassembling the bolt, a bolt disassembly tool is highly recommended, as it's a tricky, and often frustrating, operation.  I use a jeweler's screwdriver (flat), punch, and a strip of duct tape (to capture the ejector and plunger), but it's delicate surgery without the proper tool!

Since this is likely to be the first time your gun was detail stripped in a long time (almost 70 years for some guns), you might as well give it a good cleaning while it's apart.  I put the stripped parts in a bit of solvent while I'm taking them apart, and clean them with a toothbrush and oil them lightly before reassembly.  For solvent, I'll use anything from gun cleaning solvent to mineral spirits, to kerosene, brake cleaner, carburetor cleaner...use good judgement and don't be foolish, as solvents are highly flammable.  If you're nervous about flammable solvents, You can go the safe route and use a strong water based degreaser, like Simple Green or Mr. Clean Professional (purple), or even dish soap and hot water, just make sure to dry everything thoroughly when you're done.  Once it's cleaned up, everything should get a light coat of oil, grease, or some other preservative/lubricant.  I follow the advice I heard on the CMP forums, "If it slides, grease it, if it rotates, oil it."  For grease, I use Mobil 1 Synthetic (since I have a lot on hand and it's cheap and high quality), for oil I use Hoppe's, Break Free, or whatever I have at the moment...while I don't recommend it, even clean, lightweight motor oil, lightly applied, will protect everything from rust until you can find something better.

As mentioned before, the first time you fill out a data sheet, plan on at least an hour, so you're not rushing and can take your time.  Once you've done a few, you can probably crank them out in 15-30 minutes, less if you don't disassemble the bolt, and even less if you don't disassemble the trigger group.  You'll be unable to identify a few of the smaller parts (firing pin, extractor, trigger and/or sear), but you can get most of the sheet done with a simple field stripping.  

In my experience, bolt disassembly is probably the most difficult part, although it's probably easier with the proper tool.  Trigger housing disassembly is the next hardest, but fairly easy if you have a little practice and dexterity.  Everything else is pretty straightforward and not too challenging.

This is a good guide with photos on field stripping and reassembly of the M1 Carbine in .pdf form.

This is the online version of the same article.

Now that it's field stripped, let's break down the individual components.  

Here is a guide with photos on detail stripping the trigger group.

Here is a guide for detail stripping the bolt with the bolt tool.

Here is a guide for detail stripping the bolt without the bolt tool...not recommended unless you're fairly calm under pressure!

I usually fill out my sheets from the "outside in," saving the more "tricky" parts for last.  For this reason, the steps are ordered a bit differently than they are on the sheet, but I find that a simple field strip is most of what I need to do the barrel, receiver, stock (and barrel band), sights, and slide sections.  More detailed disassembly is required for some of the bolt and trigger housing sections, although you can fill out a great deal of the information without detail stripping these parts.

A thank you and photo credits to all who have helped contribute to this project, including thomasmorton21 and EARRNHARDT3 from the CMP forums.





Step 1: REPORTER AND MANUFACTURER

This is pretty self explanatory, but you have to start somewhere.  At the top of the page, put your name down where it says "Reporter."  Now we'll start filling in boxes, in the upper right corner, with the "Manufacturer" box.

Enter the:

1. Manufacturer - This can be tricky to find, as the manufacturer's name is frequently covered by the adjustable rear sight.  One way is to tilt the receiver at different angles to try to see if anything shows itself.  For example, in the first photo, the beginning of the word "Winchester" cab be seen under the rear sight.  In the second photo, the "U" for Underwood is barely visible.  In the third photo, Inland is almost completely legible...some ARE easier than others.  If you absolutely can NOT make out the manufacturer, fear not, the serial number can tell you who manufactured the receiver.  Here is a list of serial number ranges by manufacturer:

2. Name on receiver - (which, as said above, can be a trick if you have an adjustable sight, most of the manufacturer stamps are covered by the sight).

3. Serial Number - which should be behind the rear sight.  Sometimes it's repeated in other places on the receiver.

4. Code or Marking Below Serial Number - This code is usually stamped below the serial number, on the beveled area.  The photos show an example of these subcontractor codes.  The fourth photo is a Winchester "T" code, indicating the receiver was made by Intertype (code "T") for Winchester.  The fifth photo shows an Underwood "B" code, indicating the receiver was made by Singer Sewing Machine for Underwood.  It is also possible to have other variations, such as line outs (where the manufacturer is lined out  and another manufacturer is stamped below, with either their full name or a code.  These are fairly rare, and command a heavy premium, hence my inability to show an example of my own!  A Google search can provide an image if my explanation isn't making sense.

Step 2: BARREL

Right below the "Manufacturer" box, on the right side of the sheet, is the barrel information.  Examine the barrel closely, there can be any number of marks.

1.  Barrel - fill out the name exactly as it appears on the barrel.  Where it says "Date" put the date, if there is one; some barrels have the month and year, some the year only, and some are undated.  The first three photos show an Inland barrel made in May of 1944.  The 4th photo shows an Underwood barrel made in January of 1945 as examples.

2. Marks - Now scan down the barrel, looking for marks to enter in the "Marks" section.  You may find a "P" or two (as shown in photo 5), a punch mark (as shown in photo 6), an ordnance "flaming bomb" symbol (as shown in photo 4), the circled "PW" can be seen in the last photo (credit to thomasmorton21 for the photo and a thanks as well!), or a "W" indicating it's a Winchester Barrel (see photo 7).  Don't be concerned if the manufacturer of the barrel isn't the same as the manufacturer of the receiver, some manufacturers used barrels made by other manufacturers, some barrels were changed during arsenal rebuilds, and some barrels were made by Buffalo or Marlin, who made barrels but not guns.  Look also, for import marks.  Some of the more common importers were Century, Blue Sky, or Arlington Ordnance.  If you see an import mark, put it in the "Other Marks" section (see photo 8 for example). 

3. Front Sight Keyway - can usually be seen behind the front sight.  It will either be a straight cut or an "I" cut.  It's hard to see, but you can usually tell if it's one or the other.  Photos 9 and 10 are examples of the straight cut, photos 11 and 12 are examples of the "I" cut.

4. Chamber Skirt - is visible looking at the back of the barrel through the receiver.  It will be more than half the diameter of the barrel or about 1/4 of the barrel.  Check the appropriate box.  The only photo I have is of the shorter skirt (photo 13), which starts at about the 9:00 position on the barrel and ends at about the 12:00 position.  The longer chanber skirt starts at about the 4:00 position and ends at about the 12:00 position.

5. Sight Key Retention will be either chiseled or notched, check the appropriate box.  Photo 14 shows a chiseled variant, photo 15 shows a notched variant.

6. Staking of Key - can be seen by looking at the rear of the front sight.  Photo 16 shows the sight with no staking (the "None" box), photo 17 shows the top "straight line" variation, photo 18 shows the middle "punch mark on each side, centered" variation.  The last option (no photo) will be similar to photo 18, but the punch marks will be lower, touching the barrel.

7. Mark-Gas Cyl. - can be seen by looking at the gas cylinder.  Inland barrels often marked this part.  Photo 19 shows an "I-I" marked Inland gas cylinder.

8.  Mark-Piston - sometimes this part was marked, usually on Inland barrels.  Photo 20 shows a marked piston, "RI" for Inland.

9.  BBL. Color - describe the color of the barrel

10. Other Marks - List any markings on the barrel not mentioned in the above section.  I usually put any import marks (that are on the barrel) here, or sometimes I'll put "See Photo" when there are marks on the bottom of the barrel.  Inland was famous for hieroglyphics on the bottom or their barrels.  I don't think anyone's 100% sure what the marks are on Inland barrels, but they're thought to be various inspector's marks.  Photo 21 shows an example of Inland barrel "hieroglyphics."

Step 3: STOCK AND HANDGUARD

Moving to the lower left corner, you'll find the sections for the stock and handguard.

Stocks come in 3 basic styles, with a few variations in each style.  The M1 Stock, the M2 (or Potbelly) stock, and the M1A1 (or Paratrooper) stock.  The first photo shows, from top to bottom, the M1 stock, M2 (Potbelly) stock, and M1A1 (Paratrooper) stock.  The second photo shows the M1 stock on top and the M2 stock on the bottom.

The M1 Stock is what the vast majority of these guns left the factory with.  It's slimmer in the forearm area, between the barrel end and the magazine.  The earliest models had "high wood" but a later design change made the slide cutout larger and lower, and is referred to as "low wood."  The oiler slot was originally "I" shaped, but this design was simplified into an oval shaped cut later in production.

The M2 Stock was designed for the M2 (or fully automatic) model.  It is easily recognizable by the thicker (or Potbelly) forearm and the cut inside the stock for the select fire switch.  Some M1 stocks (without the Potbelly) were cut for the M2 parts.  You can determine if the stock is cut for the M2 parts by looking inside for a cut to clear the parts.  Photo 3 shows the M1 stock (with no cut) and Photo 4 shows the M2 stock (cut for the selector switch).

The M1A1 Stock is also easy to spot.  It has a folding stock and was designed for Airborne troops, to be compact and easy to carry.

The M1 and M2 stocks will usually have a manufacturer's mark in the sling well, sometimes in the slide well, and occasionally in other spots.  Most of the markings that aren't in the sling well or slide well are rebuild marks, left when the gun was rebuilt after service.  Many rebuilds were done by various military armories, but some were done by private contractors.  Photos 5-7 show various manufacturer's marks in the sling well, Photos 8 and 9 show examples of rebuild marks.

The Handguard has a few variations as well.  The sighting groove was deeper on earlier guns, and as production went on, a design change was made to make the groove shallower, to make the handguard less prone to breakage.  Photo 10 shows an early "deep groove" handguard on the left and a shallow groove handguard on the right.  The earliest models had 2 rivet holes to hold the handguard liner; later in production 4 rivets were used, as shown in photo 11.  There may or may not be markings on the bottom of the handguard which will tell you who the manufacturer is, as shown in Photo 12, with an Inland handguard on the top and a Rockola on the bottom.

So, to fill out the sheet:

STOCK

1. Stock - check the box for which type of stock you have.  M1, M2, M2 Potbelly, M1A1, or T3.  The T3 is very rare, and has a flat bottomed forend with screw holes for an infrared scope mount.  It is very unlikely you will have one of these.  See photo 1 for (top to bottom) the M1, M2, and M1A1 stocks.  Photo 2 shows the M1 stock over the M2 (Potbelly) stock.  Photo 3 shows the M1 stock with no selector lever cut, Photo 4 shows the selector lever cut in the M2 stock.

2.  Markings - List all markings on the stock.  Generally, the manufacturer's code is in the "In Sling Cut" box, the "Grip" often has a "P" that may or may not be in a circle.  Sometimes the manufacturer's code is marked in the slide well in addition to or instead of the sling well.  Other marks may be rebuild marks, rack numbers used by the unit the rifle was issued to, or markings made by other agencies that had the gun at one time...other foreign military units or police departments in the US or abroad.  Photos 5, 6, and 7 show sling cut manufacturer's marks, Photo 8 and 9 show rebuild marks.

3. Oiler Slot - is either the early "I" cut or the later (and more common) oval cut.

4. Wood at Slide -  High wood is an early feature, Low Wood is a later feature.  Many early "High Wood" stocks were cut down to "Low Wood" during arsenal rebuilds.  

HANDGUARD

1. Groove - is ether deep or shallow, check the appropriate box.  Early handguards were deep cut.  Photo 10 shows a deep groove handguard on the left, a shallow groove handguard on the right.

2. Rivets - either 2 or 4 rivets.  2 rivets was an earlier feature, 4 was a later feature.  Photo 11 shows a 2 rivet handguard on top and a 4 rivet handguard on the bottom.

3. Handguard Mark - Some handguards have manufacturer's codes on the flat spot, where it mates with the stock...not all do.  Photo 12 shows a Rockola handguard marked "RMC"

4. Liner Mark - Some liners have marks, none of mine do, so I can't provide any photos, sorry.

Step 4: BUTTPLATE AND RECOIL PLATE

This is one step I find the hardest, as Buttplate identification can be very difficult, especially on a gun with a lot of wear.  One excellent reference is found here, with better photos than I'm able to provide.

In a nutshell, if the Buttplate is checkered on a diagnal, it's an early Inland or Underwood.  Inland used 11 diamonds per inch, Underwood used 13 diamonds per inch.

Count the number of Diamonds in the Top and Bottom row.  If the buttplate is beat up, you can see from the underside much better.

*6 in the top row (outer 2 faint) 4 in the bottom row (outer 2 partial) = Late Inland or Saginaw SG
*6 in the top row (outer 2 faint) 4 in the bottom row can also be early Winchester.  Winchester Buttplates have the area around the screw hole stamped into the diamonds, which "melted" them into the dish.
*6 in the top row, 4 in the bottom row can be National Postal Meter as well, look for 4 "missing" diamonds on the top, bottom, left, and right of the screw hole
*6 in the top row, 4 in the bottom row can be I.B.M.  Look for the 4 "missing" diamonds to the left and below the screw.
*6 in the top row, 4 in the bottom row can be Saginaw SG as well, look for a missing diamond in the 5 O'Clock position by the screw.
*5 in the top row, 2 in the bottom row is Late Rockola; look for the missing diamonds at 6 and 7 O'Clock by the screw.
*4 in the top row, 2 in the bottom row can be Late Winchester, as above, look for the melted diamonds around the screw hole.
*4 in the top row, 4 in the bottom row can be Quality Hardware, look for the appearance of a border around the checkering.
*4 in the top row, 4 in the bottom row can be National Postal Meter, look for the row of 5 missing diamonds on each side of the screw hole.
Early Rockola buttplates have missing diamonds at 3 O'Clock near the screw hole.

Now to fill out the form:

Buttplate - as noted above, check the box for square or diagnal pattern.  Photo 1 shows a square cut (Winchester, I believe) Buttplate.  Photo 2 shows a diagonal (Inland or Underwood) buttplate (photo courtesy of thomasmorton21 of the CMP forums).

Marking - there may be a marking around the perimiter of the buttplate.  M1A1 (Paratrooper) carbines have a part number here as well.  B257614 is for an original buttplate, 6257614 F is for a postwar replacement buttplate.  Photo 3 shows the first variety of M1A1 buttplate.  Photo 4 shows an IP marked buttplate (thanks to thomasmorton21 from the CMP forum for the photo).

M1A1 Rivets - Brass or Steel, Tubular (hollow) or Solid.  Some rivets have marks or numbers on them.  Photo 5 shows Unmarked M1A1 brass rivets, Photo 6 shows a closer detail of an unmarked brass rivet.  Photo 7 shows the tubular (hollow) rivet of an M1A1. 

Recoil Plate - Early has a "slope" to it, later is more straight.  This is shown clearly in the drawing.  Photo 8 shows an example of the later recoil plate.

Marking and Location - Some recoil plates are marked with a manufacturer's code.  Photo 9 shows a "W" marked Winchester recoil plate, with the marking on the top.  Photo 10 shows a "PR-B" marked IBM recoil plate, with the marking on the side.

Recoil Plate Screw threaded area and head mark.  Photo 11 shows the first variation of recoil plate screw, with threads on approximately the first 1/3 of the screw.

Step 5: BARREL BAND AND SIGHTS

Taking these two sections, on the left side of the page, just above the Stock and Handguard information:

BARREL BAND

1. Barrel Band - Type 3 is by far the most common, and is easy to spot by the bayonet lug.  Types 1 and 2 are much less common.  I don't have anything with a Type 1 Barrel Band, but Photo 1 shows a Type 2 and Photo 3 shows a Type 3 Barrel Band.

2. Sling Window Width - For type 1 bands only, measure the sling window width and check the appropriate box.

3. Band Retainer - Will have one of two types of tips, and may or may not have a line from the tip to the pin.  Photos 3 and 4 show the two types of tips, both with lines.  Photo 5 shows retainer with no line.

SIGHTS

1. Front - Indicate whether the sight is Milled, Stamped, or a Casting.  Check the box for the correct sight pin staking, and indicate any marks in the space provided at the bottom of the section.  A cast sight can be determined by the casting line running around the outside of the sight. 

2. Rear - Indicate if it's a Leaf (AKA "flip sight"), Milled Adjustable, or Stamped Adjustable.  The flip sight is easy to spot, the milled is thicker, with sharper corners at the bottom, and the stamped sight is thinner than the milled, with more rounded corners at the bends.  As before, check the box for the correct sight pin staking, and indicate any marks in the space provided at the bottom of the section.  Photo 6 shows a Stamped Rear Sight, Photo 7 shows a Milled Rear Sight, Photo 8 Shows them side by side (milled on the left, stamped on the right), and Photo 9 shows them above one another (milled on top, stamped on the bottom).

3.Front Sight Shapes - This section, to the right, has examples of 6 different types of front sight.  Check the box which matches your sight.  I don't have an example of each type, but photo 10 shows a type 1 or Ridge sight, Photo 11 shows a type 2 or Grooves by Ridge sight, Photo 12 shows a type 3 or Valley sight, Photo 13 shows a type 4 or Thumbnail sight, and photo 14 shows a type 6 or No Slope sight.



Step 6: RECEIVER

This is a fairly simple step, but with a lot of sub-steps.  It's not hard at all, just take each step at a time.  On the right side of the Data Sheet, below the Barrel information is the section dealing with the Receiver.

1. U.S. Carbine Cal ____ 30 M ____, just fill in the spaces exactly as it appears on your receiver.  Handstamped receivers are uncommon, but can be determined by looking closely at the fonts, spacing, and whether they line up.  Notice that some receivers have a period both after the "Cal" and before the "30" while some only have one period.  Most guns in private hands will be M1, although a few M2 Carbines exist in private hands.  They are fairly rare and very expensive, relatively speaking.  Toward the end of production, many guns were hand stamped with either a 1 or a 2 to indicate which model it was.  Photo 1 shows 3 receivers side by side, note the difference in font, spacing, and other details.  Photo 2 shows a Winchester receiver with "Cal. .30 M1" (2 periods), while photo 3 shows a receiver marked "Cal.30M1" with one period.  The last photo shows a hand stamped serial number (thanks to EARRNHARDT3 from the CMP forums).

2. Mark if serial number is also stamped in front of sight.  The second to last photo shows an example of this (credit, again, to EARRNHARDT3 from the CMP forums).

3. Trigger Housing Lug will be one of 4 types, as indicated in the drawings.  I only have a photo of a type 4 lug, shown in photo 4.

4. Hole for Tube Lug yes or no.

5.  Operating Spring Housing will be integral (on most M1 Carbines) or detachable (on some early Winchesters and all Quality Hardware guns).Operating Spring Housing will be integral (on most M1 Carbines) or detachable (on some early Winchesters and all Quality Hardware guns).  While I can't show a photo of a spring tube housing (since I don't have one...yet...), they're fairly easy to spot, with a removable stamped tube on the side of the receiver rather than a milled integral housing.  Photo 5 shows an integral housing.

6. Rear Tang will be wide or narrow.  I only have a photo of the narrow tang, but wide tangs will run the width of the receiver, as shown in the drawing.  Photo 6 is a narrow rear tang.

7. Rear Hole There will be a hole, with or without a bushing, or no hole.  Photo 7 shows a hole (without the bushing) and a no hole receiver.

8. Mill Cut will be square or round.  Photo 8 shows a round mill cut on top, and a square mill cut on the bottom.

9. Notches Either Front, Rear, or Both.  Photo 8 shows both cuts on the top receiver, a front cut only on the bottom receiver.

10. Handguard Lip will be long or short.  The short lip is more or less symmetrical, the long lip is longer on the left side of the receiver.  Photos 9 and 10 show the long lip on the left and the short lip on the right.

Markings - Any markings you find on the receiver.  Photo 11 shows an "I" on the bottom of an Inland receiver, Photo 12 shows the "22" on the bottom of an NPM receiver.

Length - The length between the rear of the mill cut and the rear of the receiver.  Photos 13 and 14 show different lengths of this area.

Left Rear Detail.  Sorry, I again don't have photos of every variation, but you can see the difference in the 9/16" and 1/4" variations. without the ear.  The ear should be easy to spot, based on Photo 15, which shows the 9/16" on top and the 1/4" on the bottom.

Step 7: BOLT AND SLIDE

I usually do both the bolt and the slide at the same time, since they come out more or less together.

BOLT

Bolt dissassemly can be a pain in the rear, make sure you have a lot of time, a clean work area, and don't lose any small parts!  There are easier ways to do this with the proper tools, but if you don't have the specific tools, it's still possible.  I found this video on You Tube, which is long but well worth reviewing. 

Flat or Round, Blue or Park. - External examination will tell you if the bolt is flat or round, blued or parkerized.  Photos 1 and 2 show a flat, parkerized bolt on top, and a round, blued bolt on the bottom.

Marks - Write down any marks on the bolt, usually on the left or right lug, but occasionally you'll find them on other places.  Photo 3 shows a bolt with "EM-Q" on the right lug, Photo 4 shows a bolt with "IO" on the left lug. 

Right Lug Shape - either rounded or pointed.  In Photo 3, you can see the difference, with the rounded lug on top and the pointed lug on the bottom.

Gas Port in Bottom - Yes or No.  Sorry, but I have no bolts with Gas Ports in the bottom, so I can't post a photo.

Extractor - check the box for which type you have, and if there are any markings on it.  Photo 5 shows a "WI" marked Extractor.  Photo 6 shows a modified extractor, Photo 7 shows a flat extractor.

Plunger - check the box for which type you have.  Photo 8 shows the plunger with the machined flat.

Ejector Tip - check the box for which type you have.  Photo 9 shows 2 types of ejector, and you can usually tell which type you have without disassembling the bolt.

Firing Pin - check the box for which type, whether it's blue or white (unfinished), and any markings you see.  Photo 10 shows a type 2 firing pin, and Photo 11 shows a typical manufacturer's code ("W" for Winchester in this case).

SLIDE

Type - when the slide portion is completed, add up the boxes checked, and you'll get a number.

Cam Shape - either early or late.  Photo 12 shows the early type on the top, the later type on the bottom.  Photo 13 shows them side by side, with the later type on the left and the early type on the right.  Notice the early type is "flat" and the later type is angled forward.

Op Spring Guide Tip - will be pointed or blunt.  Photo 14 shows them side by side.

Arm Joint - can be one of 4 types, check the appropriate box for your type.  In photo 15, you can see the type 1 on top (with the bevel below the arm), type 2 in the middle (with the step below the arm and 3/16" area), and the type 3 on the bottom (with the step below the arm and the 9/16" area).  I don't have an M2 slide to show, but it's similar to the type 3, only with a taper where the arm connects to the slide.

Slide Box Rear - will be one of 3 types, check the appropriate box.  Show in Photo 16 and 17 are a flat slide box on the left, a full round on the right.  A part round is easy to spot from the drawing.  Photo 18 shows a detail of the flat slide box, Photo 19 shows a detail of the round slide box.

Internal Cam Cut will be flat on top or will have a "V" shape, check the appropriate box.  Photo 20 shows the "V" shaped cut.  While I don't have any with the flat cut to photograph, it's pretty easy to picture using the drawing on the Data Sheet.

Bottom view of slide - get out your micrometer, you need to measure if it's 3/32" or 2/32"

Marks - Look carefully for marks in the areas indicated.

Slide Stop -  will be one of two types, if you look carefully and move it back and forth you can tell which type you have.

Step 8: TRIGGER HOUSING

Along with the bolt dissassemly, this is the most likely step to frustrate you, as there are a lot of small parts and a couple small springs.  Keep your work area clear, take your time, and don't be afraid to do a little research before you do anything.  Once you've done it a few times, this is actually pretty easy.  You'll need a small punch for a few of the steps.

TRIGGER HOUSING - will be either an M1 or M2, either milled or stamped/brazed.  The milled trigger housings are easy to spot, as you can see the different "sandwiches" of metal when examined from the top.  In photos 1 and 2, the right most trigger housing is stamped and brazed; notice the layers of metal in front of the rear lug, and the brazing bead in the middle of the lug.

Bevels on Milled Housing - examine the top rear area, behind the trigger, to see if it's bevelled.  Examine the front of the trigger housing, in front of the magazine well, and see if it's bevelled.  Photos 1 and 2 show the bevelled lug on the left most trigger housing, and the non-bevelled lug on the later milled housing.  I don't have a photo of the housing front wiht a bevel, but it's easy to determine from the drawing on the data sheet.  Photo 3 shows a non-bevelled milled housing.

Marking - Most trigger housings have a manufacturer's mark.  Inland trigger housings are stamped with the Inland Logo, either vertical or horizontal, on the right side behind the trigger.  Photo 4 shows 3 variations on Inland Logo stamping, photos 5, 6, and 7 show them in more detail.  Photo 8 shows the much simpler "W" used by Winchester.  Most manufacturers stamped their mark in this location.  Underwood housings are often marked with a "-U-" in the back of the magazine well, as shows in Photo 9.  NPM marked many of their housings with an "N" and a number on the left side, behind the trigger housing.

Hole in left side behind mag catch - yes or no.  See photos 10 and 11 for examples of the two types.

Top View Mag Well Rear Wall - check the appropriate box for your type.  While I only have 2 variations of the same type (wide, as shown in Photo 12), the narrow type will have the back wall stop at the sides of the magazine well.  An M2 Trigger housing will have one side (the left side) stopping even with the magazine well and the other side extending to the edge of the housing.  The last photo shows a good example of the "narrow" type of rear wall (thanks, again, to thomasmorton21 from the CMP forums).

Color - color or finish of your housing

Mag Catch - check which type you have, and any marks on it.  Plain or serrated are early types, ones marked with "M" are later.  The M2 carbine had a "finger" that extended into the magazine well (to hold the 30 round magazine more securely).  Look on the side of the mag catch facing the magazine well and you can sometimes make out a manufacturer's mark.  I believe that mag catches with letters or symbols over the "M" were from arsenal rebuilds.  Photo 13 shows a typical "M" marked magazine catch.  Photo 14 shows one with a symbol over the "M" indicating it was a replacement.  Photos 15 and 16 show manufacturer's marks, Inland and Winchester respectively.

Safety - early models had push button safeties, most of these guns were arsenal upgraded to flip safeties.  Indicate which type you have and any marks on it.  Photos 17 and 18 show a plain push safety and a flip safety (different angle) showing the manufacturer's mark.

Hammer - Early hammers were "dog leg" style, and there were many variations.  Indicate any manufacturer marks and what finish you have.  You'll have to rely on the diagram, as I don't have many variations on hammers.  Mine, shown in Photo 19 and 20, are all the same type.

Sear - is either an M1 or M2, with or without a hole.  An M2 Sear has a "step" on it. Photo 21 shows, from left to right: M2 sear with hole, M1 sear without hole, M1 sear with hole.

Sear Spring - is either straight or tapered.  Photo 22 shows a tapered spring.

Trigger Marking - the manufacturer's marking on the trigger, check both sides and all around.  Photo 23 shows that manufacturer's codes were put on both sides of the trigger.

Housing Retaining Pin - will be grooved or smooth.

Hammer Spring Recess - yes or no

Hammer Spring Coils - Count the coils, you'll have 22 or 26 1/2

Hammer Plunger - will be blued or unfinished (in the white)  The last photo shows an unfinished plunger over a blued plunger.

Step 9: THAT'S IT, YOU'RE DONE!

Since the gun is all apart, I usually try to snap photos of each individual part, and upload them to a hosting service (I use Snapfish since it allows large, highly detailed photos, but Photobucket is good as well). 

Once the gun is reassembled, I usually snap photos of it all put together, and print them on the back of the Data Sheet.  I also make a list of the major components and list them, with a check mark if they're correct for the gun, sort of a quick reference guide.  My list looks like this:

Receiver:
Stock/Handguard:
Barrel:
Bolt:
Slide:
Barrel Band:
Trigger Housing:
-Hammer:
-Sear:
-Trigger:
-Safety:
-Mag Catch:
Sights:
-Front:
-Rear:
Buttplate:
Recoil Plate: