AR15 upper question

Sirex · Dec 28, 2017

So, earlier this year, I bought a new Colt 6721 Hbar rifle. I am looking at an older upper. The description says, " 1996 Post Ban without bayonet lug and flash hider, .250"Small pin Colt receiver". Is the current 6721 rifle a small hole or large hole receiver pin rifle? I am new to ARs. I did Google and I am still not sure if this will fit my new 6721. Thanks for any insight.

3paul10 · Dec 28, 2017

It will be compatible with your lower.

Sirex · Dec 28, 2017

Thanks

Rack&Roll · Dec 28, 2017

What is that etching scratched on the dust door?

clandestine · Dec 28, 2017

The front pivot pin looks badly worn on the side which may mean it is loose in another lower. It may just be the picture.

If that upper is 7.62x39 understand that other 7.62x39 bolts and extractors will likely not work as Colt used a deeper Headspace spec than modern 7.62x39 bolt do now. Colt did this to increase extractor strength.

clandestine · Dec 28, 2017

Rack&Roll said:
What is that etching scratched on the dust door?

Caliber.

3paul10 · Dec 28, 2017

I totally missed the caliber etched in the dust cover! Am I confused, this is a 7.62x39 upper to be used on a 5.56 lower??

Sirex · Dec 28, 2017

clandestine said:
The front pivot pin looks badly worn on the side which may mean it is loose in another lower. It may just be the picture.

If that upper is 7.62x39 understand that other 7.62x39 bolts and extractors will likely not work as Colt used a deeper Headspace spec than modern 7.62x39 bolt do now. Colt did this to increase extractor strength.

It is a Colt 7.62x39 Sporter upper. So even being a Colt upper, may not work with the newer 6721?

clandestine · Dec 28, 2017

Sirex said:
It is a Colt 7.62x39 Sporter upper. So even being a Colt upper, may not work with the newer 6721?

It will work as long as the lower has a .250 front pivot pin.

I'm just letting you know that Colt 7.62x39 Colts use a different bolt and extractor than the ones made by everyone else now.

Rack&Roll · Dec 28, 2017

Rack&Roll said:
What is that etching scratched on the dust door?

clandestine said:
Caliber.

Yeah, that marking was confusing for me because the thread is about a Colt HBAR and that engraving clearly says 7.62.

Edit: OK now I see that Sirex knew he had a Commie upper.

clandestine · Dec 28, 2017

Can you show me the extractor, bottom of the carrier and the bolt removed from the carrier?

Sirex · Dec 28, 2017

Ok, so just the bolt and extractor is different, but as ling as the pins and holes match, should operate on a newer Colt lower?
Rack&Roll, my Colt 6721 is a Hbar, in 5.56. I am looking at a 7.62x39 Colt upper. Sorry for any confusion. Just wanting to make sure older Colt will work on newer Colt. Debating on getting this, as I don't have the cash but the credit card has cooled a bit.

clandestine · Dec 28, 2017

Sirex said:
Ok, so just the bolt and extractor is different, but as ling as the pins and holes match, should operate on a newer Colt lower?
Rack&Roll, my Colt 6721 is a Hbar, in 5.56. I am looking at a 7.62x39 Colt upper. Sorry for any confusion. Just wanting to make sure older Colt will work on newer Colt. Debating on getting this, as I don't have the cash but the credit card has cooled a bit.

Yes, it will work with your 6721 lower. Even if it had a .312 pivot you could get a conversion pin for it or have a bushing installed.

I ask about the bolt pics baceuse lots of unscrupulous people swap parts and it would suck for you to buy something that isn't Colt or is half Colt and has issues.

clandestine · Dec 28, 2017

The side wall of the pivot lug on that upper does seem like it's worn badly like someone crushed the Colt style (screw together) pivot pin and induced damage.

Rack&Roll · Dec 28, 2017

I think now the conversation turns to: why not get a platform set up specifically for 7.62x39?

These mix-masters create problems don’t they?

That is why I bought a dedicated 9mm AR vs. a conversion.

clandestine · Dec 28, 2017

Rack&Roll said:
I think now the conversation turns to: why not get a platform set up specifically for 7.62x39?

These mix-masters create problems don’t they?

That is why I bought a dedicated 9mm AR vs. a conversion.

7.62x39 AR is often more accurate, has softer recoil, suppresses better, better ergos, and is much more easy to mount optics.

The downside is reliable mags are not a simple endeavor. You have to buy several mags/brands and test them immediately so you can return the bad ones. There are also some oddities like the difference in Colt and other 7.62x39 bolt/barrel types and 7.62x39 has different firing pin protrusion specs.

Sirex · Dec 29, 2017

These are the only 2 pics the seller has if the bolt. The upper receiver and barrel look like the whole Colt Sporter I am watching, so the exterior at least looks Colt.

Sirex · Dec 29, 2017

Rack&Roll said:
I think now the conversation turns to: why not get a platform set up specifically for 7.62x39?

These mix-masters create problems don’t they?

That is why I bought a dedicated 9mm AR vs. a conversion.

Well, I have a few 7.62x39 rifles. I wanted the Colt 7.62x39 Sporter upper because I like the flexibility of the AR to shoot various calibers, and I have a lot more 7.62x39 ammo than 5.56. The 7.62x39 AR rifles also seem to me to be more accurate. I really like the 5.56 Colt, but just adding some diversity to its diet.

Sirex · Dec 29, 2017

Best I can do blowing the pics up on my phone. I did ask the seller for better, close up pics.

clandestine · Dec 29, 2017

The bolt is Colt as is the barrel. It's legit.

Now, that unshrouded carrier. The tail is not important, but the area that has the firing pin exposed on the belly can be a reliability issue. That mod was done by Colt and other manufacturers to try and prevent people from removing parts to make the gun a slam fire auto. What it does is allow the firing pin to be damaged under operation and it adds more friction on the cocking/clcling process.

If it we're my gun, I would replace the carrier only with a fully shrouded M16 carrier, install a new firing pin, and install a Colt gold extractor spring.

Also that gun was designed (gas ported) to run on a rifle buffer, which means a standard carbine buffer will be too light. You will need an H3 buffer or heavier of you put that upper on a carbine stocked lower. The gun can have extraction issues if you don't consider this factor.

It also would not hurt to have the gun Headspace checked as many of those guns had the shit shot out of them with steel cased ammo. The barrel/throat could be reached and the gas port elongated. The barrel may look perfect to the eye, but gauges and a borescope will detect the unseen.

Just trying to offer my advice. It's a neat upper and one of the most rugged x39 uppers made for the AR.

AR15 upper question

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