Colt SP1 issues

AR/M4 Vintage ARs
1

Let me start from the beginning.

I was hired in 1989. I recall in the very early 90s shooting a full auto 20" AR platform rifle. It had the A1 type stock and triangle hand guards. I remember that day….clearly and dumping 20 round mags.

I eventually became the dept armorer (but SWAT stuff was not my responsibility). About 5 years ago, I observed a SWAT Officer assigned an A1 receiver AR as his rifle. I did a once over on the rifle and saw it was a Colt SP1 but it was not correct in that it had a heavy 16" 1/9 barrel and the hand guards were cheap A2 style. The officer wanted me to help him put optics on this rifle. The rifle concerned me as I knew there had been changes made so I got with the SWAT commander and they removed it from the line and I took possession of it. I stuck it in a corner with intentions of checking this firearm.

This rifle is full auto but missing parts (the hammer and trigger are semi auto). I recall reviewing our full auto paper work and seeing a Colt SP1 as full auto. I had asked Admin about the gun missing full auto parts and it turns out they were possibly removed by a shady officer some years back who was the armorer and suspected of stealing the parts from this gun. I told them that if this gun was originally a 20", he also took the barrel, hand guards and stock.

The stock is shiny hard plastic adjustable with two sling slots. The receiver extension was originally two position but it was drilled for multi positions.

Serial Number dates past 1982. SP16XXXX

Fast Forward to today

I dug the rifle out of my cabinet and I am glad I took it off line. The gas tube must be an original and or damaged as the build up for gas debris is heavy around the FSB and where the tube meets the gas key (meaning it was leaking gas). The A2 front sight based has cast markings and I am unable to remove the gas tube. Assuming built up debris has seized the tube in the front sight base. There is no raised area on the gas tube where it meets the gas key (as if trimmed). The barrel nut was also not very tight. I plan to pull the ATF paperwork to see what this gun was originally and now for my questions.

I doubt the PD will allow me to spin any money on this gun to try and return it to original, but I would like to get it close with least amount of cost.

Is there a resource for Mil Spec type surplus parts to get the SP1 close to original and safe too shoot? (Not necessarily Colt parts but decent mil spec stuff)

Hell, I don’t know if any of the parts left on the gun are original Colt. The bolt carrier is full auto.

I heard this officer when he left employment with us, he got hired by another dept and later got fired for internal wrongdoing. Good for him! He was long gone before we discovered and suspected he took the full auto stuff from this SP1.

There is no one left at the dept to give me the history of this gun. It may have been evidence that was awarded to our dept by the courts. I am not able to verify this was the same rifle I shot in the early 90s.

thanks in advance

2

Can you get some really good pictures of the SP1? That would help in determining exactly what you have and what you will need.

Here is a picture of my 1981 SP1 Carbine.

The barrel is stamped C MP CHROME BORE and is a 1/12 twist. If the stock looks like the one on mine, then it is a Colt vinyl acetate coated aluminum stock that was original to the SP1 Carbines along with the 2-position receiver extension. The handguards are of the 6-hole variety. How much does the one you have differ from this one besides the full-auto conversion?

3

I have the rifle completely apart right now except for the receiver extension. I will snap pics tomorrow.

Now you got me thinking…this might not be the same rifle I shot in the 90s.

The barrel I know is not Colt. Very heavy under the handguards.

4

What upper receiver does it have? A1, A2, or A3? If it has an A2 upper receiver, it could have a Colt AR6525 AR-15A2 Government Carbine upper. That had a 1/9 barrel. Not sure of the profile under the handguards. If it has an A3 upper, it could have a Colt AR6721 AR-15A3 Tactical Carbine which has a 1/9 HBAR barrel.

5

It’s an A1 upper.

6

Okay. I look forward to seeing the pictures. If you can get pics of the barrel markings, gas tube, and FSB and markings that will help too.

7

Cool…Will do.

8

I am not the best picture taker….and can take more if needed. has some paint on the lettering. I will remove. Forgot to take a picture of the other side. No forward assist.

heavy build up on gas tube

unless early gas tubes were different….this has no raised area where it meets the gas key

small parts, A2 flash hider, round hand guard cap, no full auto trigger components, no full auto selector. and enough peel washers to start a parts store

heavy barrel, not a Colt (at least I don’t think so) had many steps .980", .950" all they way to .750". regular looking barrel nut assembly.

FSB

Bolt marked MP

stock and hand guards. I was wrong on the stock, its dull plastic

bolt carrier, staked gas key but I could not find any markings

9

that’s a bushmaster barrel.

10

Legally if this gun is a F/A and owned by the PD then you can buy a full auto trigger set easy to work with that auto sear I see the gun has. Gas tube looks like it has had a good use in 3rd gear. Replace front sight base and tube. USCore replicas has old m16 stocks for sale. The gun just needs a gas tube and front sight with the m16 trigger group. Midway usa has colt m16 trigger groups for $45-50 and a regular trigger group is the same price. Also its a MG in the books so it needs to be a MG!
Your looking at about $50-300 depending on what you want to do. Barrel and stock will cost the most in your build. But you got a barrel and only need trigger group, gas tube, front sight, and stock.

11

^^^Concur.

12

If you are looking for older M-16 parts, Sarco has them.

13

Most likely, the missing raised area on the gas tube was caused by improper alignment when the Bushmaster Carbine Barrel was installed. Gas Tube alignment is something I sweat bullets over on an installation.

14

I agree. It came apart odd but will not come out of the FSB. THe barrel nut was hardly tight. I am glad I pulled this gun off line.

thanks for the info on Sarco….I will look into it.

even if this was originally a 20" rifle, I would like to make it a carbine 16" but I need to pull the paper and verify.

if they will approve the expense….it may be easier just to return it to what it once was.

15

Interesting news.

I found the ATF paperwork on this rifle and oddly enough it shows a barrel length of 12.5 inches and was converted to full auto. Approved 1988. There is no history on where this rifle originated, however the 12.5" barrel and full auto trigger components are long gone.

Also in the folder was paperwork and a single Polaroid of a 20" Colt M16 Model 614 with triangle handguards and A1 stock. That was the gun I shot in the early 90s. It was sold (to a class III dealer) along with several Ruger AC556s in 1998.

Upon inspecting the internals of the lower receiver, it shows machine work to convert to full auto.

I am sure I can just buy the proper trigger group with no administrative issues on my part (as the costs would not be that much) but the barrel would be a different story.

If this were your gun, what surplus barrel would you look at? Keeping in mind that the lower the cost the more chances I would get approval. I would also need to update the ATF paperwork.

additional pics tonight unless the tropical storm keeps me from that!

16

If its a SBR look at a 11.5"-12.5" barrel because it is a SBR and a MG and can legally be one. YMH has some good short barrels that might get you going. Also replace the front sight post because the gas tube looks like its welded to it (most likely from being shot a lot) and that’s because the gas tube looks too worn out to be safe from the only pics you took. Also its not a SP1 its a Model 653-654 from the looks of it.

17

The lower is definitely from a SP1 Sporter Carbine. It even has the original style castle nut. Several of the early SP1 receivers (pre-1986) got converted to full-auto. Is the upper receiver a slickside? It looks like it has a M16 BCG. Is that what I am seeing? The stock is not original to the weapon. It is a later fiberlite version. Originally, it would have had the aluminum vinyl acetate coated stock. It is truly a bastardized SP1. Since you plan on making it a functional full-auto weapon again, I would also suggest going with a 11.5" or 12.5" barrel. Here is a lightweight 11.5" from BCM (http://www.bravocompanyusa.com/BCM-Standard-11-5-Carbine-Barrel-light-weight-p/bcm-brl-s-11lw%20std.htm). You would need a .625" FSB for it. They also have other 11.5" and 12.5" barrels that are .750" at the gas block. What you have can be made into a really nice retro full-auto SBR.

18

Yes, the upper is slick. I forgot to snap that image. Yes…M16 BCG with no markings.

Reference using a modern barrel and FSB……will there be an issue with front sight height with the A1 fixed rear?

I am assuming I would have to find a barrel with a FSB that is not “F” marked??

19

Not a real issue. I have a XM177E2 that I built using an A1 upper and an A2 FSB (non- F marked) with an A1 FSP in it. I have no issues with accuracy with it. The important thing is to have the A1 FSP. I have a 723 build with a Colt C H upper (A1) and a F marked FSB with an A2 FSP. No issues there either.

20

Renegade, do you have a link for an image on your XM177E2?