How to remove a Colt Sear Block
 

Introduction:

The Colt Sear Block is a extra piece of hardened steel that Colt added to their lower receivers to prevent the addition of a Drop In Auto Sear or Lightning Link to their receivers. In addition, the rather creative location of the pin used to hold this sear block in also prevented the drilling of the receiver for the addition of a traditional M-16 sear as well. Colt added these stupid blocks by their own choice and there is no legal requirement for these so they can be removed if the owner oof one of these Colts wanted to do so.

The sear block sometimes causes problems for people that wish to use some after market triggers and it obviously causes problems for people with registed DIAS and LLs. In addition, M-16 carriers including 9mm Bolt Carriers cut to M-16 profile will hit the top of a sear block. Normal AR-15 carriers including closed and open Colt "C" type carriers will work with the sear block without any need of modification.

The purpose of this thread is to show some methods that can be used to remove these sear blocks. Colt is the only manufacturer to use these sear blocks.

Following is a post from AR15.com that is being reposted with the author's permission:

Originally Posted By RamblinWreck:
http://ar15.com/forums/topic.html?b=...2&t=202184

I got tired of looking at the blocks in my 2 Colt prebans, and when I couldn't install RRA 2-stage triggers because of them, they had to go. I have done this twice now, and if you are very careful, you won't scratch your lower, at least not on the outside. The drill it/Marvel mystery oil/hydraulic method has been proven to be bunk by a few that have tried it, besides, whenever you push the blind pins out it creates an ugly raised lip on the aluminum at the edge of the hole. My method leaves the pin in and preserves the stock exterior look of the lower. PS these lowers only had one blind pin thru the side; I have seen some with two and even three blind pins thru the side of the lower - this won't work on those - you'll have to mill those out. Here's how I did it:

Strip the lower internals and find some duct tape. Using a Dremel with a new cut-off disc (buy the little jar full of them - you're going to need a lot of them), I first CAREFULLY make a thin cut thru the block close to the edge of the lower, and then a second one down thru the raised portion of the block - you need clearance here for the Dremel shaft to make the 1st cut as deep as you can. I used a bit of Kroil as a cutting agent and went slowly - I still broke a lot of wheels.

http://quarterbore.com/images/colt_sb_removal_01a.jpg

1st cut is started on right, 2nd cut thru the raised portion almost done.

http://quarterbore.com/images/colt_sb_removal_01b.jpg

Make a sideways cut to remove the piece of upper block.

http://quarterbore.com/images/colt_sb_removal_01c.jpg

Cut the thin slice as deep as you can, use some tape on the lower so the Dremel shaft doesn't mar the finish. You want to cut thru and well below the blind pin. I then cracked off the thin piece by bending it back and forth. Once this is done, grab the block with a big pair of channel lock pliers and wiggle it until the inside blind pin (a roll pin) breaks and the block can be wiggled forward and out. All done.

http://quarterbore.com/images/colt_sb_removal_01d.jpg

Another view.

http://quarterbore.com/images/colt_sb_removal_01e.jpg

Pin is still in, looks stock.

http://quarterbore.com/images/colt_sb_removal_01f.jpg

Good luck. HTH

How about the new colt sear blocks, where the block is actually part of the lower receiver mold? Just dremel it down to mil-spec?

Thanks

I am curious if you can post a picture... this would be more complicated and it is likely a challange best attempted with a Milling Machine. In as much, a good gunsmith or machinist might be best unless you are lucky enough to have your own mill in the garrage. There would be nothing to prohibit you from milling your receiver to SP-1 specs as long as you DO NOT DRILL the autosear hole... Drilling the hole for the autosear makes the receiver an M-16 (10-years in jail and $100,000 in fines for that little hole!)

Sure.... here's 3, it may take a while to load (its off my home server).

http://12.218.219.175/e/100_0932s.JPG

http://12.218.219.175/e/100_0934s.JPG

http://12.218.219.175/e/100_0935s.JPG


Rifle is a Colt Match Target Match HBAR, post-ban. MT6601 i believe. (unsure of exact model).

Well, if you are good I am sure you could dremmel it away... If you were local we could work on getting my Bridgeport Mill running and I am sure we could do a good job...

PA is too far of a drive for a simple sear-block removal... I could do it in under a half hour if i went slow with a dremel and used a caliper....


Thanks :)

Not to beat a dead horse!
 

I am trying to install an RRA NM trigger in one with this problem, are there any other issues you are aware of since this thread was put to bed. I have a machinist/gunsmith who will cut the block out for me, just want to be sure I am not barking up the wrong tree. Any help appreciated!
"Molon Labe"
Al

Removal is pretty simple, set the lower in a mill vise and use a 3/8 end mill to mill it out. Stay out of the Alum side wall. If you are dealing with the new style that has a block that is actually part of the lower find the true center of the lower bring your tool in and make a cut on each side to create the correct opening, be mindful of depth as well. In the past I have copied a
low shelf receiver to get the correct dementions. The material is soft and so a HSS end mill will work fine, how ever carbide makes the project a breeze. 20-30mins. :wink: