I have an old Colt Match Target HBAR with the block on it and I really need to replace the Bolt carrier…I cannot get an M16 Bolt carrier to fit there with the stupid block…see photos below…can this be filed down legally? If the block is made flush with the receiver, it would appear that the M16 bolt carrier or at least a shrouded carrier could be used. this is a nice rifle and I would hate to let it go, especially since nobody wants to buy it unless I give it away…help…
Why do you need to replace your carrier?
It is not that I must, but I am not happy with it being the unshrouded type, and while I do not shoot this rifle a lot or in life threatening situations, I just think I would like the heavier bolt carrier with the shroud to protect the bolt. My 6920 has an M16 bolt carrier and I would like this one to have one too.
Take a look at my carrier below.
My recommendation is that you NOT molest a factory original Colt from the Colt gray period of anodizing. Those rifles have a uniqueness that is worth preserving. If you want to switch the rifle up, just buy yourself a new rifle configuration.
I speak from personal experience here. I ground down and moly coated the steel sear block in my blue label Colt 6551 and while I truly did a great job, I wish I had just left the lower factory.
These green label, blue label, white label, etc… Colts will truly be collectibles one day; it is up to us to preserve them for future generations.
Please no one take this to mean that I don’t run my guns hard. I shoot the snot out of mine. It is just that I believe the early Colt AR15s and the transitional 1990s Sporters, etc have a special place in collecting and should be preserved.
OP, I have a Colt carrier that has a shrouded firing pin but has the half circle rear.
SAW used to sell them as “semi auto LE cocking angle”, but they no longer carry them.
you won’t get any added mass, but you’ll get the shrouded firing pin
IM me if you’re interested, i’d rather part out my MT6400C than see you trash your Colt lower
https://www.m4carbine.net/showthread.php?t=40453&highlight=block
Just get a AR15 enhanced carrier as mentioned in the linked threads,and use the original bolt…don’t shave the sear block or any of the other stuff.Put the obscene unshrouded half circle Colt carrier away in your safe or parts box,that way the rifle can be put back into original state in the future if your worried about collector value.No harm,no foul.
HTH
Yes it is legal to remove or machine the block. It was never a requirement of ATF’s and there is a letter from them stating it is ok to remove.
Below is the ATF letter and a link to it.
DEPARTMENT OF THE TREASURY
BUREAU OF ALCOHOL, TOBACCO AND FIREARMS
WASHINGTON, DC 20226
NOV 5 1997 F:SD:FTB:RLB
3311
Dear :
This is in response to your letter of October 23, 1997, to the
Bureau of Alcohol, Tobacco and Firearms. In your letter, you ask if
removing the steel receiver block from the lower receiver unit of
a Colt, Sporter rifle would be a violation of Federal law.
The steel receiver block to which you refer, is intended to serve
as an anti-tampering device and prevents the installation of
various AR-15 drop-in auto sears, lightning links, and M16
machinegun fire control components. The steel receiver block is
installed in the sporter lower receiver unit by Colt Firearms and
is an attempt, on Colt’s part, to prevent the illegal conversion of
their semiautomatic sporter lower receivers units into machineguns
style receivers. The presence of the steel receiver block is not
required by Federal law.
Based on our research, it is our opinion that the removal of the
steel receiver block, in and of itself, from the lower receiver
unit of a Colt, Sporter rifle would not result in a violation of
Federal law. In addition, the possession, sale, or transfer of a
Colt, Sporter lower receiver unit with the steel receiver block
removed would not constitute a violation at Federal law.
We trust that the foregoing has been responsive to your inquiry. If
we may be of any further assistance, please contact us.
Sincerely yours,
Edward M. Owen , Jr.
Chief, Firearms Technology Branch
ADCO professionally removes the sear blocks. Another option would be to buy a semi carrier. LMT and DD would be the ones that I would recommend.
Since I live in a ban state, I have a number of pre ban Colt lowers with sear blocks and I am seriously considering grinding them off so I can use FA carriers. Since I got rid of the Colt uppers already, the “colletor’s” value is not much.
Also, my preban Colt 9mm, had the top part of sear block ground down at the factory so it could use 9mm carrier.
I have 2 pre ban large pin colt lowers if you want one to replace it with
I still say the simplest,and most fool proof solution is to get a AR15 enhanced carrier and run it like it is.Upgrade will take all of 5 minutes to do.
Main goal is to gain the reliability of the shrouded firing pin,and the .5oz. or so weight difference between the AR15 and M16 carrier is not going to make a lick of difference in how that target Hbar runs.
I sure would not go through the trouble of trying to remove the block or pay to have it done for such little in return.
YMMV
ETA
xcibes,
I have to say that is a perty gun…very nice.
Xavier, as others have stated, the easiest thing to do is run an enhanced AR15 carrier…but since it’s not a collectable preban, if you really want it gone, then I’d give ADCO a call and see what they’ll do for you.
Thanks guys! I think I will go for the enhanced bolt carrier…The main goal was to get the shrouded bolt and I think that will do. As to collector value…while it is a nice rifle, I do not have the box or original packing material, plus it has been rebarrelled…it now has a GI barrel instead of the HBAR…so it’s nowhere near original condition anyway.
I re-read your original post and now realize this is a Match Target (and thus post-94), not a Sporter Target (which would be a pre-94). I retract my recommendations regarding collectibility…hack away.
The shroud does nothing to protect the bolt. 
It just makes the carrier cock the hammer instead of the firing pin.
ADCO is your friend.
I have a Sporter lower with the same block and it runs just fine with an AR-15 BCG.
I had a wtf moment last week when I saw one of these BCG’s (and knew something about the platform) for the first time last week. On this particular colt the front takedown pin was a factory bolt. I am curious if yours is that way too.
Not sure I follow you…the front takedown pin is just a pin not the screw/bolt-type one on the SP-1
As to the shroud not protecting the bolt…well, on a recent article by none other than our very own rob_s on how to make your M4 run, it said unshrouded bolt carriers were no good because by the bolt cocking the hammer, it may get bent…better saf than sorry I say though the chances of this are rather small.
It is NOT the bolt but the firing pin that cocks the hammer on an unshrouded carrier.
I was unaware that what I looked at was an SP-1. I was told it was a 20 inch HBAR. Was there a point to bolting the front of the receiver? I was offered the rifle for $1200 and I may have to pass. That seems like an awful high starting point.