Digging through some archived research info on my hard drive, I found the following written by Jack at Public Safety, who has been a major Colt LE supplier for decades. The detail goes well beyond what is normally found in resources like The Black Rifle. I thought I'd share it:
I was throwing out some old paperwork and found a bunch of notes I have kept over the years of Transferable Colt production AR15 and M16 guns I have seen.
Here is the info: Colt AR15 and M16 serial number ranges Observed. Doesn’t include Colt Tool Room or Gun Room marked guns. Not meant to be all knowing or exclusive.
Colt AR15 Serial Number under 010 – Some have No logo – Tool Room Guns with distinctive tool marks on receiver. There are at least 3 guns serial number #0004 attributed to Colt. Not to be confused with Armalite SN: 0004.
Colt AR15 Model 01 – SN: 000,1xx: Usually has green painted bakelite furniture.
Through
Colt AR15 Model 01 – SN: 015,2xx
Colt AR15 Model GX – SN: 014,5xx : Adjustable length Buttstock and 10” barrel
Colt AR15 Tool Room Shorty – SN: 014,864: Adjustable Buttstock, 10” barrel, cut down triangular handguards, very short muzzle suppressor.
Colt AR15 Model 08 – SN: 015,5xx: Survival Rifle (Estimated Less than 10 made)
Colt AR15 Model 07 – SN: 015,59x: Adjustable Buttstock, 10” barrel, cut down triangular handguards, short muzzle suppressor.* “GX” model range. One gun has no Colt markings and it is in Model 07 configuration with all the paperwork showing it was exported to a NATO country before 1965 and returned before 1968.
-Note: Also noted are additional so called “GX” shortys, or “Government Experimentals”. Guns are marked AR15 with a serial number, but also a GX drawing number. At least one gun is registered in the NFA twice under the serial number and again under the GX number. Very rare, only seen one in private hands and one in a Museum. These were tested in Vietnam and Laos by Special Forces and CIA officers. Some originally came with the Survival Rifle cone flash hider.
Colt AR15 Model 05B – SN: 015,6xx: Tool Room Carbine model. Very few made due to malfunctions. 14.5” cut down barrel with triangular handguards, 4 position selector, Chrome bolt.
Colt AR15 Model 06 – SN: 015,65x: Tool Room Heavy Barrel Squad Auto.
Colt AR15 Model M2 HBAR belt fed – SN: 018,9xx: Less than 20 made as belt feed action. At least one is still in the white.
Colt AR15 Model 02 – SN: 023,8xx: Usually US Property marked. 3 prong flash hider.
Colt AR15 Model 02 – SN: 038xxx: Prototype 16” barrel carbine. Cut down handguards with longer barrel for better functioning. US Property marked & usually with 4 position selector. May have 2, 3 or 4 shot burst ratchets.
Colt AR15 Model 02 – SN: 039,7xx: Standard US Property marked 02.
Colt AR15 Model 04 – SN: 040,0xx: Property Marked with no forward assist. Marked M16. Has XM16E1 style mag release fence. Only one I have seen was a reweld from GI scraps from the 1970’s. Very rare gun as a transferable.
Colt AR15 XM177E2 – SN: 111,xxx: US property marked and marked XM177E2. 11.5” barrel with chrome chamber, round CAR15 handguards, and collapsible stock. Barrel usually marked “C MP” under handguards or under barrel in front of front sight leg.
Very rare, as only one seen, and it had been refinished. Had SEAL Team platoon graffiti scratched on the right mag well.
Colt AR15 XM16E1 – SN: 145,9xx: US Property marked, and marked XM16E1. Trial model.
Colt AR15 Model 656 – SN: 2012xx: Tool room experimental SNIPER with handleless Upper receiver, heavy barrel, modified gas system and ART scope.
Colt AR15 Model 606B – SN: 20243x: Heavy assault Barrel, M14 bipod, triangular flash hider, may have green painted furniture. US Government purchased less than 200 guns.
Colt AR15 Model 610B – SN: 202,44x: Colt Tool Room Shorty. Solid collapsible stock, 10” barrel, 4 position selector. Chrome carrier with no forward assist.
Colt AR15 Model M16A1 – SN: 605,xxx: US Property marked standard rifle. Vietnam era gun and for export.
Colt AR15 Model 609 – SN: 900,07x: Marked US Property and “COMMANDO”. May or may not have modified selector assembly. 10” or 11.5” barrel with flash suppressor/moderator. Only two have been seen, serialized within 500 numbers of each other – there can’t be 500 of the Commando series, but we can only hope.
Colt AR15 Model GAU 5A: SN: 902,xxx: Marked US Property with 11.5” barrel and no forward assist. US Air Force contract. Still in use by US Air force security police. Never seen a transferable gun.
H&R M16A1 – SN: 2,004,14x: Harrington & Richardson licensed built: US Property marked. Forward assist.
H&R highest observed was 2,220,000.
GM M16A1 – SN: 3,000,xxx: GM Hydromatic Division built under license. US Property Marked. Forward Assist. Two have been observed as Form 5 Deactivated Guns mounted on wall plaques. Very rare as non-reweld.
Note: There are at least one of each maker: H&R and GM built XM177E2 rifles. Part of the original contract for the M16 required both companies to bid on manufacturing the XM177E2 shorty. Of the two I have observed, both appeared to be made from parts and not original. An original documented XM177E2 made by either company would be worth a premium if documented. Parts would have to be from Colt. GM did have Colt data sheets on the XM177E2 model specific parts.
Colt AR15 Model 651 – SN: 4,378,2xx: M16A1 style receiver with 14.5” carbine barrel and CAR15 stock.
Colt AR15 – SN: 4,574, 6xx: Sold as Possible Tool Room gun. Special finned 10” barrel. Marked “COMMANDO.” Vertical pistol grip added to round front handguard, purportedly from MAC SOG test gun. Another stripped XM177E2 marked gun from 110,xxx serial number range found in Colt tool room before move to West Hartford with hang tag from Vietnam, noting severe damage to upper and front sight due to firefight with NVA regular troops. Noted that handguard was modified for control: i.e. front grip. Probably an export gun since not US Property marked and earlier parts added.
Colt AR15 Model 639 – SN: 4,790,xxx: Export model of XM177E2. 11.5” barrel with chrome chamber, sliding buttstock, 4” stovepipe suppressor with spacer, and forward assist. Receiver marked “AR15 and Model 639”. No property marks. Guns rarely have factory applied serial numbers on suppressors. Premium applies if it does. Most have “IRS” number etched or scratched on suppressor body. Should not have a bayonet lug.
Colt M16A1 – SN: 4,705,72x: US Property Marked full size rifle. Some were tested as the M16A1E1 predecessor to the M16A2.
Colt M16 Model 640 – SN: 5,016,xxx: Export model of XM177E1. 11.5” barrel with chrome chamber, sliding buttstock, 4” stovepipe suppressor with spacer and no forward assist. Can sometimes be found with correct, Colt proofed upper receiver with forward assist, vice no forward assist. Finish is usually dark black. Serial number can be as high as 5,096,xxx and be accurate. At least three production runs done of this model. Most are in the 5,016,xxx range. Should not have a bayonet lug. Most will have their factory correct barrel and flash hider – all are factory marked barrels – Caveat Emptor as there have been at least 25 sets of XM model gun uppers sold since 1994.
Original Colt boxes for the XM and 639/640 guns were as follows: 41' L x 9.5' D x 3 1/8' H. Only markings are on the This rifle is covered by the Following US Patents, (new line) 2,903,809 2,951,424 3,027,672 3,045,555 3.090,150'
The inside of the box has a green spun plastic packing that reminds one of the Easter egg basket pack of your youth. Boxes are rare after all these years. I I had 25 in my old shop, but lost them in the fire.
Colt AR15 Model 613 – SN: 5,080,5xx: Standard rifle configuration. Closed birdcage flash suppressor.
Colt M16A2 – SN: 6,00,xxx: US Property marked. Very few original Property marked M16A2’s out there. I have only seen 1 in person and heard of 4 others.
Colt M16A2 – SN: 8,000,xxx: Export and police market version. Highest pre86 gun I have observed was numbered in the 8,002,xxx range – there may be some in a higher range. There are some Post 86 guns numbered below that so original paperwork or BATF FOIA would apply. Two types of finish. Earlier guns have medium grey Sandstro finish on lowers and later guns are all Black MILSPEC.
Colt M16 – SN: 9,050,xxx: Standard rifle configuration, forward assist with closed birdcage flash hider. Correct from Colt to a CA railroad police agency.
Colt M16 Model 629 – SN: 9,075,3xx: US Property marked with 11.5” barrel, sliding stock and 4” suppressor. Possibly a parts gun.
Colt M16A1 – SN: 9,105,77x : Atchisson open bolt HBAR conversion on standard Colt M16A1 rifle with M14 bipod. Predates the Colt designed open bolt HBAR. Marketed by W.A.K. in Ohio.
Colt M16A1 Model 653 – SN: 9,288,1xx: 14.5” barrel with forward assist upper and sliding stock.
Colt M16A1 Model 653 – SN: 9,577,17x: Personal 14.5” barrel with no forward assist upper and sliding stock.
Carbine serial numbers range as high as 9,955,xxx. Liberally distributed throughout export M16A1 serial range. Several 651/2 solid stock and carbine upper guns were made and sold to Colt dealers during the early 1970’s. Very rare configuration, but nice handling gun. Many original concept 651's were numbered in the low 400,000 range, but are very rare.
Colt M16A1 Model 606A – SN: 9,560,6xx: Referred to as HBAR assault rifle. M60 bipod with standard triangular handguards.
Colt M16A2 Model 635 SMG –SN: HT000001 through HT005xxx. Colt 9mm SMG. Transferable guns range from 50 to as many as 125. My personal SMG was serialed in the high 5xxx range and it was transferable. My post sample 635 was serialed in the mid 2xxx range and it was a post sample. Who can figure. BATF FOIA on the Form 2 from Colt would apply.
There are 6 prototype 9mm SMG’s. All have grip safeties like a 1911A1 Colt pistol. Three of these guns are in a private collection.
Special series:
M231 firing port guns. Surprising that there are quite a few transferable guns. Fun to shoot with tracer, as designed - but will set things on fire from the fire thrown from the ejection port. All I have seen were US Property marked with an 'X' prefix. I do not remember the production serial number range.
Cross Section Training guns:
AR15 marked guns: Usually “X” prefix.
Other experimental guns have a “X” prefix vice the GX prefix Colt usually employed.
Some M16A2 cut a ways in rifle and carbine configuration were made before 1986. Should have a “X” prefix, but not necessarily. There are few of these up for sale in PA and ID. Would be nice to know.

What can you folks tell me about these guns? I just purchased a really nice one with a 4' barrel from the original owner who got it new in 1977. From what I've read the Troopers are built on an extremely strong frame and can take about anything in terms of ammunition. I've also read that they are sometimes considered the poor man's Python. Anybody here have any experience with them? I will post pictures when I get mine, but it may be a while until I get through the transfer, etc. I gave $400 for it and it appears to be barely fired. Fair price?