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Discussion Starter · #1 · (Edited)
I really would like to go to a flattop upper receiver to be able to use a red dot sight etc... I currently have a early 1990's Colt Sporter Lightweight with the A2 fixed carry handle. It has the "pencil" barrel that has been cut and has a vortex flashider permently attached for a length of 16.1 inches. Its been outfitted with a Magpul CTR buttstock and a Magpul MOE carbine forestock, also a Surefire G2 light. Its very light and quick. The only nagging drawback is its not a flattop and I would like to put a Aimpoint on it. Here are a few of the optons that I've been looking at:

1. Leave as is and buy a Colt 6920. Drawback is the cost of the new rifle and buying more Magpul parts. And it does not have the pencil barrel that I prefer.

2. Purchasing a BCM upper with a lightweight barrel assembly and fitting it to my Colt lower.

3. Purchasing a Colt upper and use my barrel on it. Also I would need to pickup the tools to do this barrel install.

4. Send my rifle to Colt and have them install the M4 upper on my rifle.


The downside to most if not all the rifles out there for me is that they do not use the pencil barrel, and this is a must. Please give me your thoughts and advice.

Thanks, Jim
 

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Depends on what YOU want to do. The most expedient way to go would be to buy a flat top upper and install it your self. The major conern with commercial Colts is the lower rx pin size. Do you know what size the pins are? If they are not milspec size there are some conversion pins available.

In and of itself changing out a barrel is not that big a deal. Some of the tools can be improvised such as the barrel jaw clamps. What you'd need would be a roll pin punch for the front sight base/gas tube retaining roll pin and a barrel nut wrench after the gas tube is removed.


Here are a couple of websites that talk about the large pin/small pin Colt lowers.
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http://pullig.dyndns.org/retroblackrifle/LowerBldGde.html

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http://cheaperthandirt.com/blog/?page_id=96
 

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If you get a goose neck for the aimpoint, you don't have to do anything.
 

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I'm with you, I too like the "pencil" barrels on a carbine. Light and quick as you say.

You've obviously put some time and effort into getting your rifle set up the way you like, except for the fixed carry handle. Early 90's time frame I suspect you have the fat two-screw pivot pin that attaches the upper to the lower at the front. This does limit your options somewhat, but there are M4 flattop type stripped uppers out there with the big pin hole.

I have fooled around with using the little adapter widgets to adapt a small pivot pin milspec upper to a Colt big pin lower and I don't like them. They tend to rotate when you pop the gun open shotgun style for maintenance, and then bind up so you can't close the gun again without a screwdriver to fiddle with the adapter until it will close. Could be bad if you had to pop it open to clear a malfunction of some sort in a hurry. After I figured this out I now make a point of having matching upper/lower assemblies with the right size pin. Maybe I'm paranoid (OK, not maybe. GI1)

I would suggest getting the correct stripped upper with the proper pin hole setup and just swapping it out. That saves all of your custom work and the barrel you know and like. You need the barrel nut wrench and an upper receiver vise block set, Brownell's has good ones. Also a tube of the correct milspec grease for the barrel nut threads. Don't poo-poo this last item, if you use any old bearing grease or whatever on the barrel nut threads there can be a galvanic corrosion problem that will eat the aluminum threads off the upper and weld the barrel nut on permanently... Skygeek.com sells the proper milspec grease, it's used a lot on airplanes for bearing and whatnot. A tube will last the rest of your life.

Swapping out an AR upper is incredibly easy if you can walk and chew gum at the same time and use a torque wrench. Get a copy of the M16/M4 military armorer's manual (they are all over the web) and follow the instructions and torque specs and rock on with your flattop...

EDIT: Does your barrel and upper have M4 extended feed ramp cuts?
 

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What is your budget?

Colts have held their value fairly well. Sell the Colt and buy another carbine configured the way you want it. Remove the Magpul furniture and re-install the original.

There's nothing wrong with buying another upper configured the way you want it. Check the Palmetto State Armory website to see if they offer what you want. They have good uppers and good prices
 

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...a tube of the correct milspec grease for the barrel nut threads. Don't poo-poo this last item, if you use any old bearing grease or whatever on the barrel nut threads there can be a galvanic corrosion problem that will eat the aluminum threads off the upper and weld the barrel nut on permanently... Skygeek.com sells the proper milspec grease, it's used a lot on airplanes for bearing and whatnot. A tube will last the rest of your life...
Good point about the grease. The stuff you need to avoid is the copper anti-seize. Nickle based anti-seize will not cause corrosion. Standard non-moly grease will also work fine
 

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My understanding is that any grease that has ingredients that conduct electricity is bad, especially graphite. Graphite is very common in automotive bearing greases.

The correct grease is GREASE, MOLYBDENUM DISULFIDE: LB (81349) MIL-G-21164
per the TM.

AeroShell 33MS EP grease is rated MIL-G-21164D:

http://www.skygeek.com/aeroshell-33ms.html
 
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Discussion Starter · #9 ·
I'm with you, I too like the "pencil" barrels on a carbine. Light and quick as you say.

You've obviously put some time and effort into getting your rifle set up the way you like, except for the fixed carry handle. Early 90's time frame I suspect you have the fat two-screw pivot pin that attaches the upper to the lower at the front. This does limit your options somewhat, but there are M4 flattop type stripped uppers out there with the big pin hole.

I have fooled around with using the little adapter widgets to adapt a small pivot pin milspec upper to a Colt big pin lower and I don't like them. They tend to rotate when you pop the gun open shotgun style for maintenance, and then bind up so you can't close the gun again without a screwdriver to fiddle with the adapter until it will close. Could be bad if you had to pop it open to clear a malfunction of some sort in a hurry. After I figured this out I now make a point of having matching upper/lower assemblies with the right size pin. Maybe I'm paranoid (OK, not maybe. GI1)

I would suggest getting the correct stripped upper with the proper pin hole setup and just swapping it out. That saves all of your custom work and the barrel you know and like. You need the barrel nut wrench and an upper receiver vise block set, Brownell's has good ones. Also a tube of the correct milspec grease for the barrel nut threads. Don't poo-poo this last item, if you use any old bearing grease or whatever on the barrel nut threads there can be a galvanic corrosion problem that will eat the aluminum threads off the upper and weld the barrel nut on permanently... Skygeek.com sells the proper milspec grease, it's used a lot on airplanes for bearing and whatnot. A tube will last the rest of your life.

Swapping out an AR upper is incredibly easy if you can walk and chew gum at the same time and use a torque wrench. Get a copy of the M16/M4 military armorer's manual (they are all over the web) and follow the instructions and torque specs and rock on with your flattop...

EDIT: Does your barrel and upper have M4 extended feed ramp cuts?
Thanks for all the good input here.

To answer your question about the feedramps; Yes my 1992 rifle does have the M4 feedramps in the barrel extension and in the upper. And yes I have put alot of thought getting it set up the way it is. Just a lean, mean fighting machine. No extras other what I have mentioned. A member on another forum suggested I get a whole other rifle setup like I want with a pencil barrel, etc. Trouble is I have not seen any that would be of at least Colt quality. I'm open to this. Any suggestions?
 

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I, too, have an early '90's big pin H-bar. Wanting something a little lighter and more manuverable (like my Socom16...) I investigated the conversion pins for a new upper, but, like 2336 said, they leave a bit to be desired. I wound up getting a LRB lower and buying a completed RRA midlength upper built exactly the way I wanted. Did I pay a bit more than just buying a new rifle...? Probably, but there were a few things I wanted specifically for my build and, in the long run, I probably saved money over buying a rifle and modifying it.

I initially was going to sell my H-Bar to fund the new rifle, my wife talked me out of that... and I'm glad she did. So now I have 2 AR's... the big A2, and my shorty.

As far as Colt, they build a good rifle... but they are not All That and a bag of chips. There are plenty of good manufacturers of complete rifles, completed uppers and replacement parts. The beauty of the AR system is it's complete adaptability to what you want.

If you wanted to go the less expensive route, I would find a used A4 Colt big pin upper and swap your parts, and there is even the possibility you could find a complete take-off upper.
 

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Discussion Starter · #11 ·
I, too, have an early '90's big pin H-bar. Wanting something a little lighter and more manuverable (like my Socom16...) I investigated the conversion pins for a new upper, but, like 2336 said, they leave a bit to be desired. I wound up getting a LRB lower and buying a completed RRA midlength upper built exactly the way I wanted. Did I pay a bit more than just buying a new rifle...? Probably, but there were a few things I wanted specifically for my build and, in the long run, I probably saved money over buying a rifle and modifying it.

I initially was going to sell my H-Bar to fund the new rifle, my wife talked me out of that... and I'm glad she did. So now I have 2 AR's... the big A2, and my shorty.

As far as Colt, they build a good rifle... but they are not All That and a bag of chips. There are plenty of good manufacturers of complete rifles, completed uppers and replacement parts. The beauty of the AR system is it's complete adaptability to what you want.

If you wanted to go the less expensive route, I would find a used A4 Colt big pin upper and swap your parts, and there is even the possibility you could find a complete take-off upper.
Thanks for the great advice. Mainly because of the front pin issue I may leave my A2 LW as is, maybe add a set of XS tritiums to make myself feel good.

This very well may turn out to be a great excuse for another rifle. I just spent the last hour specing out the parts for a BCM rifle done just like my A2 LW but with a flattop instead. Counting its cost plus the Aimpoint this is getting to be more then I wanted to spend however I'll still have my old lightweight, which is very very nice, plus a brand new BCM. Sounds like a plan, huh.
 

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I tried to go the whole "swap out uppers whenever I wanted to change config" route. Somehow I ended up just buying more lowers to mate with the uppers so instead of 1 rifle, I have 4. Not that this is a bad thing mind you... :)

I would definitely lean towards a complete rifle for the above reason.

Oh, and if you buy parts, expect to pay alot more than a complete rifle. It's a joy to build it yourself but you usually end up on the high end of the $$ range.
 

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I don't see a big problem - buy a "dogleg" or drop mount and put a red dot or reflex, etc, coaxial with your iron sights. I too love the pencil barrel and the quick handling, and light weight.

I have used the Trijicon Reflex on a Colt Government Carbine with the 12 minute amber triangle set up like this and it is awesome! At close range you cover the center of mass with the triangle and shoot. At long range you use the point of the triangle as you aiming point. And the irons are right there, should you ever need them.

The correct, large hole flat top uppers are available, should you just want to go straight flat top.

Oh, and by the way, Colt ARs ARE all that and a bag of chips. Colt is the Standard for production ARs. They developed the gun from Stoner's somewhat flawed prototype and have produced over 8 Million of them. Their plant has Government Inspectors and the raw material for even vendor supplied parts has to be lab tested before it can be released for production. They have specs and hold to them. Everyone else can build to whatever spec - or no spec - they want. The end user will never know - until it breaks or wears out prematurely. The little shops are NOT comparable to a large, dedicated manufacturing facility with constant military oversight. But the clone makers buy advertising in the gun rags and so they get good press. They are generally cheaper for a reason. CC
 

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My understanding is that any grease that has ingredients that conduct electricity is bad, especially graphite. Graphite is very common in automotive bearing greases.

The correct grease is GREASE, MOLYBDENUM DISULFIDE: LB (81349) MIL-G-21164 per the TM.

AeroShell 33MS EP grease is rated MIL-G-21164D:

http://www.skygeek.com/aeroshell-33ms.html
Yup, use Moly-B.
 

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I don't do large hole lowers but I have swapped several Colt light weight barrels onto flatops. At the time you could find Colt uppers at reasonable prices, no longer the case. Daniel Defense makes a large hole flatop upper, I would find one of these and find someone local who could swap out my barrel.
 

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Greetings,

I did essentially the same thing some years ago. Wanted a flat top for a scope on my Colt HBAR and all the other "M4" kind of stuff. I used a (now out of business, but good products at very good prices) Anvil Arms A4 upper. It came out just fine, but it also ended up bothering me after a while that I somehow "disgraced" my Colt.

So, the A4 upper became a starting point for another AR and the Colt went back together with most of the original parts. At some point, I'll likely put it entirely back to factory with the A2 stock and all. That will leave more parts for yet another build down the road. Can't recall your specifics, but be sure your barrel extension feed ramps will match up to a new upper if you go that way. Mine did not have the M4 cuts so I got an upper that did not.

Guess the moral of my story (at least what I learned) would be to leave a Colt as is and build up another rifle to your spec. You'd also be in a better financial position to sell the Colt in factory trim if things went that way. I've always kept all the original parts removed from any of my "frakengun" projects.

Regards, Jim
 

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Discussion Starter · #17 ·
Thanks to everyone for their input. This is what I ended up doing;

I decided to keep the rifle mentioned in my opening post the way it is. My heart just was not into changing it. Its very sweet the way it is. I have ordered a set of XS tritum front and rear sights for it.

Here is where I went with my option number 1, adding a second rifle. This way I could keep my A2 the way it is and add a flattop. I got very lucky and was able to find a Colt 6720 that was made in a limited run for Clyde Armory. I plan to outfit this one like my other rifle, keeping it very simple and lightweight. Only being able to add a red dot sight because its a flattop.

The red dot sight that I plan on mounting is the Aimpoint M4S. My sons rifle has the Eotech XPS3-0 which I really like, but I decided to try the M4S. Any thoughts on this would be welcome.

Thanks, Jim
 

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Thanks to everyone for their input. This is what I ended up doing;

I decided to keep the rifle mentioned in my opening post the way it is. My heart just was not into changing it. Its very sweet the way it is. I have ordered a set of XS tritum front and rear sights for it.

Here is where I went with my option number 1, adding a second rifle. This way I could keep my A2 the way it is and add a flattop. I got very lucky and was able to find a Colt 6720 that was made in a limited run for Clyde Armory. I plan to outfit this one like my other rifle, keeping it very simple and lightweight. Only being able to add a red dot sight because its a flattop.

The red dot sight that I plan on mounting is the Aimpoint M4S. My sons rifle has the Eotech XPS3-0 which I really like, but I decided to try the M4S. Any thoughts on this would be welcome.

Thanks, Jim
You chose well.

Aimpoint > EOTech, especially in the latest generation models such as the M4 series and the Micros.

Only things I would add would be a dedicated weapon light at 10 o'clock (on a Larue, DD, GearSector, Vltor, or other quality mount) and a vertical foregrip (such as a TangoDown stubbie). Lastly, a two point sling and plenty of PMAG's.

Again, couple of great choices...keep us informed!
 

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Discussion Starter · #19 ·
You chose well.

Aimpoint > EOTech, especially in the latest generation models such as the M4 series and the Micros.

Only things I would add would be a dedicated weapon light at 10 o'clock (on a Larue, DD, GearSector, Vltor, or other quality mount) and a vertical foregrip (such as a TangoDown stubbie). Lastly, a two point sling and plenty of PMAG's.

Again, couple of great choices...keep us informed!
Thanks for your encouraging words, it seems we think very much alike. I 've been in this gun thing for a very long time and have been fortunate to have had guidance and companionship from some of the best in the country. I could tell some stories.

As for the equipment: My existing rifle has a Surefire G2 mounted in a Vltor mount, mounted at 10 o'clock to the side of the front sight post. I plan on doing the same thing to the new 6720.

Both rifles are/will be fitted with Blue Force Vickers two point slings. 20 and 30 round PMAGS is pretty much all I use any more. On the forend I prefer a un adorned MOE handguard.

Thanks for your thoughts.
 

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Thanks for your encouraging words, it seems we think very much alike.
Wow - we sure do! My weaponlight? Surefire G2L in a Vltor Scout Offset mount (old style with the thumbscrews). I'm looking hard at the GearSector...heard a few good things about it. Also, thinking about just buying another X300 and calling it a day.

My next build's going to be a 14.5", 1/7 twist pencil barrel, probably a middie this time with a PA'd BattleComp. And instead of a rail system - MOE handguards!

Looking forward to pics when you're complete :twothumbsup:
 
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