View Full Version : Colt MT6400 (6920) extractor upgrade kit info wanted?
I have a Colt MT6400 which is a post-ban compliant version of the 6920 M4/AR15A4 carbine. I built a MK12ish upper to use on my lower.
Looking at Brownells catalog and website I saw a extractor upgrade kit which has a stiffer spring, extractor buffer and rubber doughnut that slips over the coil spring to increase the extraction force to four times the factory rating. I'm using a Centurion Arms C4 BCG in my MK12ish build which came with the doughnut over the coil spring and extractor.
My Colt only has the coil spring and extractor buffer. I've never had any trouble at all with it extracting spent cases. It's boring reliable. That being said, is it worth getting the upgrade kits and installing them on all our AR's (they're all 5.56 so far)?
Thanks, NYH1.
Simply put: No. The Colt "Gold" colored spring with the black insert does the job admirably. No need for the o-ring or other extra, super, duper spring if you have had zero issues with extraction.
ETA: http://www.specializedarmament.com/products/Extractor_Spring_Assembly_Colt-190-292.html
Unneeded excessive extractor tension is not needed for most. For a combination that does not need that, there are better solutions available. Excess tension in this area can take work away from other functions for completing the cycle, among other issues that do not help things. Shaving brass, extractor claw and pin wear/stress, etc do not help. Use only as much extractor force as required with a minor safety factor, excess is not needed or recommended.
Ok, thanks guys.
What about my Centurion Arms C4 BCG that has the doughnut setup? Should I just leave it the way it came.
Thanks again, NYH1.
The O ring was only meant to be used until Colt found a solution to the extraction problems with the M4. They developed the 5 coil extractor spring with a rubber buffer. It solved the problem. The O ring is not to be used with the Colt 5 coil spring & rubber buffer. I think the spring is referred to as the "copper" spring
Many people do not grasp the importance of balancing extractor and ejector forces. For this reason, I suggest combos. Colt ejector and extractor springs pair niceley. Ken Elmore also has an extractor spring that I like a lot. Maybe more than colts. Right now, I'm running the Sprinco extractor and ejector. They are working very well. Rubber o rings are to be avoided imo
platoonDaddy
02-28-16, 04:43
BCM has an upgrade kit with O-ring, that takes muscle to install or mechanical tool.
BufordTJustice
02-28-16, 12:57
Many people do not grasp the importance of balancing extractor and ejector forces. For this reason, I suggest combos. Colt ejector and extractor springs pair niceley. Ken Elmore also has an extractor spring that I like a lot. Maybe more than colts. Right now, I'm running the Sprinco extractor and ejector. They are working very well. Rubber o rings are to be avoided imo
Agreed. I am all SprinCo now as well with their 5 coil extractor spring.
the automator
03-01-16, 15:38
BCM has an upgrade kit with O-ring, that takes muscle to install or mechanical tool.
I use that without the O Ring on a 10.5" along with an H3 buffer and it runs like a dream.
We use the Sprinco extractor spring in all of our BCG's. It works very well. I would also just recommend grabbing a few at once for any future needs or other AR's.
Wayne Dobbs
03-02-16, 09:40
The "O-Ring" was developed by NSWC-Crane for ONE problem gun: the Navy Mk 18 10.3" barreled system that had serious extractor failures due to shortened lock time from running a suppressor on same and increasing gas system pressures. Folks not being aware of the context of the development of this ring immediately decided they had to have it 'cause "the SEALs use it so it must be great". It is good for the Mk 18 and similarly situated type SBRs, it's likely a neutral on the 14.5-16" guns and it's a NO GO on the 20" rifle systems where its quadruple increase of extractor tension can and will lead to failures of the bolt to close and lock.
Thanks guys. So I guess I'll remove them from our Centurion Arms C4 BCG's. One is being used in a MK12ish build 18" barrel rifle length gas system. The other will be going in a 20" rifle build.
I wonder why Monty would puts them in their BCG if they're not needed. Maybe he figures most will use them in SBR, IDK.
Thanks again, NYH1.
Thanks guys. So I guess I'll remove them from our Centurion Arms C4 BCG's. One is being used in a MK12ish build 18" barrel rifle length gas system. The other will be going in a 20" rifle build.
I wonder why Monty would puts them in their BCG if they're not needed. Maybe he figures most will use them in SBR, IDK.
Thanks again, NYH1.
The Colt "Gold", Ken Elmoor "Green", and Sprinco 5-coil are all 3 EXCELLENT choices, and none of which require the O-ring for ANY combination.
Navuy SEAL Syndrome is what I tell people in my classes as well.
The "O-Ring" was developed by NSWC-Crane for ONE problem gun: the Navy Mk 18 10.3" barreled system that had serious extractor failures due to shortened lock time from running a suppressor on same and increasing gas system pressures. Folks not being aware of the context of the development of this ring immediately decided they had to have it 'cause "the SEALs use it so it must be great". It is good for the Mk 18 and similarly situated type SBRs, it's likely a neutral on the 14.5-16" guns and it's a NO GO on the 20" rifle systems where its quadruple increase of extractor tension can and will lead to failures of the bolt to close and lock.
The "O-Ring" was developed by NSWC-Crane for ONE problem gun: the Navy Mk 18 10.3" barreled system that had serious extractor failures due to shortened lock time from running a suppressor on same and increasing gas system pressures. Folks not being aware of the context of the development of this ring immediately decided they had to have it 'cause "the SEALs use it so it must be great". It is good for the Mk 18 and similarly situated type SBRs, it's likely a neutral on the 14.5-16" guns and it's a NO GO on the 20" rifle systems where its quadruple increase of extractor tension can and will lead to failures of the bolt to close and lock.
Why is this? Are rifle springs that much weaker than carbine springs? My experience with Vltor's rifle spring in my A5 leads me to think they might be.
Thanks again guys, I really appreciate it.
NYH1.
In layman's terms is because the 20" rifle and gas system is the most optimal for dwell time, extraction, etc..
Why is this? Are rifle springs that much weaker than carbine springs? My experience with Vltor's rifle spring in my A5 leads me to think they might be.
Agreed. I am all SprinCo now as well with their 5 coil extractor spring.
Have you run the 5 coil Sprinco's on any rifle length gas system? I just ordered a few 5 coil and 4 coil springs but saw that Sprinco suggested not using the 5 coil springs on rifle length gas. Just curious if anyone has had any experience first hand. I'll try it personally when I get mine, I'm curious if anyone else had tried it.
BufordTJustice
03-05-16, 08:18
Have you run the 5 coil Sprinco's on any rifle length gas system? I just ordered a few 5 coil and 4 coil springs but saw that Sprinco suggested not using the 5 coil springs on rifle length gas. Just curious if anyone has had any experience first hand. I'll try it personally when I get mine, I'm curious if anyone else had tried it.
I do run them on my 18" faxon gunner with rifle gas. No issues. Same with my Rainier Arms Mountain Series 18" with rifle gas. Never a problem.
I do run them on my 18" faxon gunner with rifle gas. No issues. Same with my Rainier Arms Mountain Series 18" with rifle gas. Never a problem.
Thanks for the info. I have a 18" and 20" heavy fluted Faxon barrels I was going to be using them with. So it sounds like I should be good to go.
BufordTJustice
03-05-16, 14:00
Thanks for the info. I have a 18" and 20" heavy fluted Faxon barrels I was going to be using them with. So it sounds like I should be good to go.
You're all set, brother.
sinlessorrow
03-06-16, 12:18
The "O-Ring" was developed by NSWC-Crane for ONE problem gun: the Navy Mk 18 10.3" barreled system that had serious extractor failures due to shortened lock time from running a suppressor on same and increasing gas system pressures. Folks not being aware of the context of the development of this ring immediately decided they had to have it 'cause "the SEALs use it so it must be great". It is good for the Mk 18 and similarly situated type SBRs, it's likely a neutral on the 14.5-16" guns and it's a NO GO on the 20" rifle systems where its quadruple increase of extractor tension can and will lead to failures of the bolt to close and lock.
That was also back when the M4 used the old M16 extractor springs.
The 5 coil copper colored(called gold) extractor spring didn't finish Army testing and see adoption until 2007, this is why the O-ring even existed.
It's no longer needed with the current extractor spring.
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