Colt M4 Carbine  BORE CHARACTERISTICS  Hard Chrome Lined, 6 Lands & Groves, 1 Twist in 7 in. (178 mm), Right Hand  
http://colt.com/mil/M4_2.asp

Colt MT6400C

http://colt.com/CMCI/MTM4.asp

Other than obvious internal and/or external differences, is the civilian Colt MT6400C fundementally the same rifle as the military Colt M4 Carbine ?
The civilian section of Colt's website does not have as specific descriptions as the military section.
Is the Colt MT6400C bore hard chromed lined? (ETC)

I have a Colt 6400c and the barrel and chamber are chrome lined, also has the feed ramp cuts. The second question I had when I purchased mine was the barrel length, the 6400 has the 16" barrel not including the compensator.

I purchased a new FSB with bayo lug from raptor22 (thanks) and an A2 flash suppressor with crush washer from Specialized Armament Warehouse waiting for the AWB sunset. I will probably get the old style collapsible Colt stock from SAW as well if they have any left.

Besides the AWB restrictions and the lack of full-auto the 6400C is exactly the same weapon that's issued.

I have the stock pinned in a different position that I am satisified with, so after the ban ends I'll have the FH added, but thats about it.  A Colt brand collapsible stock will be added as money allows.

If the military is using 55grain then why the 1/7 twist?

Quoted: If the military is using 55grain then why the 1/7 twist?

Because the military doesn't use 55grain primarily Even if they did, 55gr ammo shoots just fine in a 1/7ROT barrel.

There are some units with older 1/12ROT barreled rifles who are still issued 55gr M193, but M855 is the standard now.

Edited to add: Here are some pics of my own 6400C to give you a better idea of what it's about:

The Colt 6400c has an M4 marked upper and lower:




Heavy duty "H" buffer and heavy duty extractor spring for reliability:




Barrel has proper 1/7ROT, chamber and barrel are chrome lined:


Upper is RAS numbered:


Side sling mount:


Standard pushpin lower and no protruding searblock:


Proper M4 handguards with dual heatshields:


Proper M4 entended feedramps:


Lifetime service agreement:

Quoted: If the military is using 55grain then why the 1/7 twist?

So they can shoot the heavier loads, still the 55gr ammo isn't used that often in M4's.  I shoot 55gr all the time in my M4 but I think the military standard is the green tip 62gr.  

They should be using 55gr though cause it has better terminal balistics out of 14" barrels at the ranges they shoot.  62gr makes nice little ice-pick holes.

Quoted: Proper M4 handguards with dual heatshields:

I remember someone here bashing Colt's hand guards because they didn't allow proper barrel cooling.  I told them that’s exactly what they're for!!!  My hands don’t feel a damn bit of heat cause those double shields are WORKING!  They were bashing them to prop up their product though (I wont mention who).

Thanx for the info.
One more question, please.

Is the MT6731 the same as the  MT6400C except for the stock, barrel and brake?
Thanx in advance.