Colt AR6721 Ten-Step Transformation


Start with a stock Colt AR-15 A3 Tactical Carbine (AKA a Colt AR6721) . . .

Step 1. Replace the factory barrel assembly with a Noveske stainless-steel Recon barrel assembly including a set-screwed and taper-pinned low-profile gas block.

Step 2.  Replace the factory handguards with a Geissele 13” SMR MK8 M-LOK free-float handguard.

Step 3.  Replace the A2 flash-hider with a Smith Enterprise Vortex flash-hider.

Step 4.  Install Knight’s Armament front and rear back-up iron sights.

Step 5.  Replace the factory fire control group with a Geissele SSA-E fire control group.

Step 6.  Replace the A2 grip with a Magpul MIAD grip.

Step 7.  Replace the factory trigger-guard with a Magpul aluminum enhanced trigger-guard.

Step 8.  Replace the factory buttstock assembly with a Magpul UBR buttstock assembly.

The transformed carbine (without a weapon mounted light or optic mounted) weighs-in at 7 pounds, 12 ounces.



















Step 9.  Install a Schmidt & Bender Short Dot LE in a LaRue Tactical SPR-E mount.










Step 10.  Add a weapon mounted light, sling, bipod or fore-grip as needed.







Arisaka In-Line M-LOK mount.






Magpul cantilever M-LOK mount.






Magpul off-set M-LOK mount.




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While evaluating the accuracy of various hand-loads from the Recon barrel, shooting from a bench-rest at a distance of 100 yards and using the Short Dot LE set at 4X magnification, the Recon barrel produced the 10-shot group pictured below using Sierra 55 grain BlitzKings.  The group has an extreme spread of 0.77".
















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In before the safety guys have a fit about the first pic.





I like the UBR, but the rest isn't my flavor. This is one of the test mules, correct?

"In before the safety guys have a fit about the first pic."


LOL...you win the internet today with this.




Gorgeous Rifle. +1


 

Nice rifle!

I like it!

Nice rifle, but the scope is outta my price range, big time. How's it shoot??

While evaluating the accuracy of various hand-loads from the Recon barrel, shooting from a bench-rest at a distance of 100 yards and using the Short Dot LE set at 4X magnification, the Recon barrel produced the 10-shot group pictured below using Sierra 55 grain BlitzKings.  The group has an extreme spread of 0.77".
















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A beautiful rifle done right.

Very nice

I like what you've done with yours, with better accuracy than the factory barrel with FF rails that you posted before a long time ago.

I've also got a 6721 that I bought new in 2010 with small FCG pins, got a pretty good light and smooth factory trigger, the best Colt trigger I have ever had, and it still got the LE restricted markings on the right side magwell.

I'm just going to do mine the poor man's very slow transformation to a Dissipator type in three very slow phases.

Phase I - done now
Step 1: Installed KAC M4 RAS rail system
Step 2: Installed Troy (old anti cant mounting design) folding rear sight
Step 3: Replaced grip with Magpul MIAD grip
Step 4: Installed BCM bolt extractor upgrade kit (not using the O-ring)
Step 5: Replaced CH with BCM GF mod 4 medium latch
Step 6: Replaced mag catch with Norgon ambi
Step 7: Replaced selector with LMT ambi
Step 8: Replaced M4 stock with Vltor IMOD

With my Aimpoint on LaRue LT129 QD cantilever mount and Surefire M961C unloaded weight is a whopping 9.5 pounds.

Phase II Next
Step 1: Shave FSB and remove delta ring
Step 2: Replace rail system with an older Samson Mfg. 12" FF two piece rails (mounts on std barrel mount)
Step 3: Install folding or fixed front BUIS on rail system

It would be heavier than before because of the longer rails so I'll replace my light with a lighter model Surefire.

Phase III Final work
Step 1: Remove rails and barrel to contour under handguard similar to SOCOM profile tapered 0.800" to 0.850", turn fixed FSB area to 0.625" front end of rail, mount FSB 0.625" type with tapered pins
Step 2: Install reworked barrel assembly
Step 3: Install AAC Blackout FS
Step 4: Remove front BUIS from rail
Step 5: Re-install Samson rails

With my re-contouring the barrel I know I will group slightly larger than your 0.87" 100 yd 10 shot group that you did with your factory HBAR barrel, I'll be happy with a slight sub 1 MOA.

Do you still have the image of your 0.87" group with the factory barrel with FF rails, if so could you post it?

Would I encounter any possible problems with my plan?

ETA.  I just found this pic.  It might be the one you're referring to.  (I've owned 3 of the Colt 6721 barrels) . . .






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I'm moving my fixed front sight forward about 5 inches and the barrel diameter close to the muzzle is only about 0.720" so I have to make a next smaller size gas block journal there for my non working FSB (rifle gas location), my real gas block is just my old carbine gas length shaved FSB under the 12" rifle handguard.

This 6721 is my second carbine I also have an older same 6721 I bought new old stock in 2005 but it was actually made in 2002.

I sold the factory barrel new and I replaced it myself with Denny's Guns Operator midlength, medium contour, fixed proper F FSB, Rock Creek Barrels blank, contoured, chambered and assembled by Compass Lake Engineering at FL. I also installed a LaRue Tactical 9.0 FF rail system back in late 2005.

Thanks for posting that grouping pic, close enough but I found the old thread with the 0.87" grouping (archive link below).


http://www.ar15.com/archive/topic.html?b=3&f=118&t=470522

Step 11: Replace the upper and lower receiver with an Aero matched set
Step 12: Replace Colt BCG and charging handle with equivalent BCM parts
Step 13: Assemble all the replaced parts into another complete AR

 


Nice work, Molon.  For optimum accuracy, I suggest you try Sierra's 53 grain Matchkings instead of the Blitzkings.  My 5.56 rifle with its 1in8 Green Mountain barrel does best with these. - CW

]

Clean.  That S&B is a sweetie

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Nice group!  I've done a fair amount of accuracy/precision testing with AR-15s using a wide variety of bullets, including the 52 grain SMK, 53 grain SMK and 55 BlitzKing. From the majority of the more than 40 AR-15s barrels that I've owned, the 55 grain BlitzKing has been the most consistent in producing the smaller groups out of those three bullets.

Every Barrel Is A Law Unto Itself.






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Outstanding, Molon.  10 rounds from an AR-15 into .474" CTC at 100 yards takes the cake.  You should frame that target and hang it on the wall for all to admire.  If I can routinely put 10 rounds into an inch at 100 yards from my plain jane 5.56 rifle with its chrome-lined Green Mountain barrel, I've often wondered what I could do with a purpose built AR based on a heavy match barrel like your Krieger tube.  I'm feeling some BRD envy - CW

Barnes 85 grain Match Burner.  10-shot group at 100 yards from Krieger barreled AR-15.  

Extreme spread = 0.428"







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Got it.

Look at the Steiner 1-4 military on sale at euro optic for $699.00.  Best value for the money on 1-4 optic out there right now.

Did you take any shots with it before the modifications?  I'm curious how much improvement there was from stock...

The Steiner or Burris XTRii are a good investment as is the Vortex Razor.  I've become one of the buy once cry once crowd, over the last few years.  Those S&B's are very nice. Nice job on your Colt, OP.

Momma wants granite countertops.  She may kill me if I buy more glass  

Negative.

I think it's currently one of my favorite optics.

I call her Margaery.


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I miss the picture of the dog with the red solo cup wind meter, and the picture of the rests on the bench holding a rifle

 

Nice write up.


Do you prefer different size/shape targets for different magnification or reticle configurations?

Inquiring minds want to know, what is Molon's powder and charge weight when loading 55 grain Sierra Blitz Kings?

OAL"?

Post the usual warnings about work up etc.

Impressive. Thanks for sharing.

Too much BCM Kool Aid, Colt is, IMHO, better than BCM on the BCG and the charging handle is a WTF? etc.
As to the upper & lower, that's just to satisfy your fanaticises, nothing to do with accuracy.

I would name it, too.  I am in the market for some nice glass to go on my planned KAC 11.5 upper...

Damn you!

When shooting match-grade hand-loads with a high magnification scope, I prefer my target with the off-set aiming point.







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