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9/22/2017 12:11:25 AM
Posted: 9/22/2005 8:10:19 PM EDT
Have a dumb question maybe.

I have a 6721LE. I replaced the BC with a LMT M-16 BC. I was reading and got confused when i saw That Colt shaves the bottom of there bolts to fit the sear blocked lowers. I have ran about 6-800rds through it since with no trouble. Is this something i need to worry about doing damage to internals or something else? I know the newer LE models have M-16 BCG's included, are they the same size as LMT's? or different in diameter to fit with the blocked lower?

Thanks?
Link Posted: 9/22/2005 8:16:44 PM EDT
[Last Edit: 9/22/2005 8:23:42 PM EDT by theshootersden]
Nothing to worry about... The sear block that interferes with the full auto bolt carriers is the one that has COLT stamped onto the top of it... Its a block of steel inserted into the sear relief area and its pinned to the lower to prevent easy removal... The 6721 has the "web" sear block and doesn't interfere with the bolt carrier, it does though prevent the use of some aftermarket triggers though...

Edited because of to many thoughs
Link Posted: 9/22/2005 8:18:40 PM EDT
You have a different form of sear block. You're good to go.

The ones that need a shaved bolt, AKA half circle, have a seperate piece pinned in the sear area making it impossible to put in a M16 trigger group or an auto sear. I beleive your lower simply has an unmilled area in the lower where a sear would normally rest. This is the new model sear "block" even though it is just an area they didn't finish milling on the machine.
Link Posted: 9/23/2005 2:33:21 AM EDT

Originally Posted By theshootersden:
Nothing to worry about... The sear block that interferes with the full auto bolt carriers is the one that has COLT stamped onto the top of it... Its a block of steel inserted into the sear relief area and its pinned to the lower to prevent easy removal... The 6721 has the "web" sear block and doesn't interfere with the bolt carrier, it does though prevent the use of some aftermarket triggers though...

Edited because of to many thoughs



Whose triggers won't work? JP trigger and hammer fire kit work just fine.
I know rra won't work, but that is due to pin size and not some web.
Link Posted: 9/23/2005 2:39:00 AM EDT
[Last Edit: 9/23/2005 2:39:32 AM EDT by Colt_SBR]
My SBR is a pre-ban Colt lower. It has the sear block that interferes with the full auto bolt carriers that has COLT stamped onto the top of it. I tried to install a M16 carrier and found out, it won't work.

I've been using a RRA enhanced carrier without problems. Guess I'll stick with the RRA carrier. Someday, I might have the sear block shaved down.

Link Posted: 9/23/2005 6:08:35 AM EDT
[Last Edit: 9/23/2005 6:24:04 AM EDT by theshootersden]

Originally Posted By Gregory_K:

Originally Posted By theshootersden:
Nothing to worry about... The sear block that interferes with the full auto bolt carriers is the one that has COLT stamped onto the top of it... Its a block of steel inserted into the sear relief area and its pinned to the lower to prevent easy removal... The 6721 has the "web" sear block and doesn't interfere with the bolt carrier, it does though prevent the use of some aftermarket triggers though...

Edited because of to many thoughs



Whose triggers won't work? JP trigger and hammer fire kit work just fine.
I know rra won't work, but that is due to pin size and not some web.



RRA will work with a COLT blocked receiver too, you need to get their large pin (.170") 2-stage trigger

As for the exact trigger I experienced trouble with, It was something a friend had purchased off of gunbroker that was for the large pin COLT's and I cant remember which brand it was... I had to dremel a small portion of the trigger to fit his COLT 6721... Later today I'll see if I can find out what brand it was...
Link Posted: 9/23/2005 6:34:52 AM EDT
I have a Colt lower with the "COLT" marked sear block; absolutely no functional problems with a standard, full-circle AR-15 carrier (CMT).
Link Posted: 9/23/2005 7:08:31 AM EDT
I have a pre ban Sporter with the "Colt" stamped block in it, and it will not close completely to allow the rear push pin to work when I put my Colt 6920 bolt carrier in it.

I guess there'e some variance in the Colt carriers, or perhaps the sear blocks. Does anyone know if it's a problem (Legally) to mill out the web in a 6920 to accept a drop in sear?
Link Posted: 9/23/2005 7:16:17 AM EDT
[Last Edit: 9/23/2005 7:19:26 AM EDT by Gregory_K]
you can remove the block, but do not mill enough out to accpet a auto sear.

your 6920 carrier dosen't work because it is an m16 carrier.

did not know rra made a 170 pin size nm.

With the JP you have to fit the triggger to the saftey, they sell it on pourpose extra large. that and most of the time you have to time the disco. All this is true for any lower.
Link Posted: 9/23/2005 7:25:50 AM EDT
I'd just like to add that I hate that sear block in my pre-'94 Colt Gov't. Carbine. Not that I plan on doing anything illegal, it's just that block is obtrusive and annoying. It makes it hard to clean all the gunk out of the lower when I am cleaning every detail. Not to mention it's just plain ugly the way it sticks out of the receiver like some sort of tumor.
Link Posted: 9/23/2005 7:35:52 AM EDT
I've seen where people have the "Colt" sear block removed and the pins stay in. I've also seen where they removed the sear block and left holes where the sear block pins were.

If I have mine removed, I'll have it milled down to match the upper edge of the lower.
Link Posted: 9/23/2005 7:52:49 AM EDT

Originally Posted By Colt_SBR:
I've seen where people have the "Colt" sear block removed and the pins stay in. I've also seen where they removed the sear block and left holes where the sear block pins were.

If I have mine removed, I'll have it milled down to match the upper edge of the lower.



you can do this yourself on a bench grinder. just don't overheat the work, having a water ponge handy helps. a little blueing creme after and your done. i have done three this way, and it works perfect with m16 carriers.
Link Posted: 9/23/2005 8:28:51 AM EDT
Those are nasty little critters:



Last year Colt's used those was about 1997. I cut mine out of my older 6551. If you have one with only one pin then I recommend cutting it out, ain't that hard:

ar15.com/forums/topic.html?b=3&f=12&t=202184


Link Posted: 9/24/2005 4:39:52 PM EDT

Originally Posted By Ekie:
Those are nasty little critters:


Wow, I never knew they were that "deep"! Good keychain fob for those in the know.
Link Posted: 9/24/2005 4:50:51 PM EDT
[Last Edit: 9/24/2005 4:51:08 PM EDT by Ekie]

Originally Posted By Kisara:

Originally Posted By Ekie:
Those are nasty little critters:


Wow, I never knew they were that "deep"! Good keychain fob for those in the know.



Never thought of that, think I tossed mine, those things are creepy like a tumor, don't like having them around.
Link Posted: 9/24/2005 5:15:24 PM EDT
If anyone has removed one and wants to get rid of it, I'll take it. I need and nice key fob for my Harley.


I don't think I have the guts to do mine.

Link Posted: 9/24/2005 5:30:31 PM EDT
Link Posted: 9/24/2005 5:33:33 PM EDT
6yeah i relized that after the post.
Link Posted: 9/24/2005 5:48:50 PM EDT

Originally Posted By Tweak:

Originally Posted By Gregory_K:
but do not mill enough out to accpet a auto sear.



be hard to fit an autosear when there is that big hole where the pin for autosear used to be.



I never understood why they would try to block an auto sear and drill the auto sear hole in the process.
Link Posted: 9/24/2005 6:13:53 PM EDT
Link Posted: 9/24/2005 6:36:41 PM EDT
[Last Edit: 9/24/2005 6:37:35 PM EDT by npd233]
Check out the photos in this thread

www.ar15.com/forums/topic.html?b=3&f=12&t=251315
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