I don't know anything about full auto on and AR and what it looks like, but on a Colt as seen below, am I seeing correctly that there is an extra pin hole above the safety?  Wouldn't that make it a "machine gun" by all definition?

Looks too big to be an auto sear. Most likely a sear block.

Not always. From what i understand that could be a colt with a factory sear block installed. Someone with more knowledge of Colt lowers with sear blocks may be able to confirm it.

It's a Colt sear block.  

~Augee

This.

ok, So it is not auto.  So the point of the pinned in sear is to prevent drop in auto?  Forgive me I have never looked into this.

Yes, and hi heroin bob.

"Well, it's a crazy fucked up world and we're all just floating along waiting for someone who can walk on water, man."
Classic movie

I did enjoy the movie, reminded me of all of my old friends.  Many of them dead now.  

So back on topic, so a sear block is like the rivets in the old saigas that came in with the 3rd hole except the sear block hole is bigger than the pin for a auto sear?

Really wished it was auto and I could of got it at sub 5k.  You know what they say about too good to be true.

Well... if someone was determined enough I'm sure they could come up with a way to make that gun full-auto.  Just remember, after the first felony the rest are free.

Hey, I thought I recognized that picture. I took it a few years ago for a similar discussion (I think that one was more related to Colt's non-standard mods, though).

Here's another picture showing the sear block pin from the left side.  As noted, the pin hole was placed there intentionally. It is larger than the auto-sear pin hole, and is also drilled off-center from where the auto-sear pin hole is located.

Any notion why Colt was so utterly anal about preventing full-auto conversions when it was not required by law?  They surely went to a hell of a lot of trouble back then.
Moon

They thought they were being "forward thinking" by seeing the writing on the wall and re-acting to it.  Regardless, Colt was wrong and, for a long time from the 80s onward, it really cost them.



In the 60s and 70s, Colt ARs were advertised with a 5 ( or 10 ) round factory mag instead of a normal 20.  Don't know if they were originally delivered that way, though. Another dumb move.





Modern Ponies are properly set up.  Small FCG pins, proper front push pin, etc.  They also redid the auto sear block so that you can used fully shrouded carriers...which they now deliver,also.





 

Nope, your sear block is to prevent F/A, the hole is a different size.  Nothing illegal about it.
Also, slightly off center for a full auto sear.

The changes did not occur all at once.  

Originally when Colt released the SP1 configuration - larger pivot pin, no sear relief on the upper, and cut back carrier they had to get the modifications approved by the ATF as "not readily convertible" to the civilian definition of a machine gun.  Remember that this was pre-1986, when it was legal to buy new production automatic weapons as NFA items.  

The idea was you couldn't simply drop in a new military upper and an M16 FCG and illegally create a machine gun.  One way or another, it's what was required to get ATF approval to sell the AR15 commercially.  

However, again, since this was pre-'86, you could also legally convert semi-automatic firearms to fire automatic with a Form 1, and both the Lighting Link and Drop-In Auto Sear were developed in response to the SP1 modifications.  

Colt, for better or worse, seeing the writing on the wall regarding restrictions to come, and under a lot of fire for being pretty much the only well known commercial manufacturer of a "easily convertible rapid fire baby killing engine of destruction" introduced new features to prevent the easy conversion of semi-automatic rifles into automatic rifles using the LL and DIAS - that is to say, by installing a blind pinned sear block where a DIAS would go, fully cutting back the carrier, preventing the use of a LL, and changing the size of the FCG pins so that you couldn't just install an M16 FCG in the receiver.  

Understand that Colt was under a lot of scrutiny at this point, they were no less visible as they are today - no one was really playing close attention to what SGW or Quality Parts or Eagle Arms was doing - they had about the same prominence in the public consciousness as Mega or LMT has today, that is to say, those in the gun-owning community may be aware of them, but the average person on the street has never heard of them, and doesn't care what they do, but they almost certainly have heard of Colt, and know that they make guns.  

Once they went to the larger FCG pins and sear block, they also dropped the large pivot pin dimension and non-standard uppers, though there was a transitional period - most likely while they used up the components and forgings they already had on hand.  

Ultimately, though, it ended up making no difference, and the AWB came anyways, and in the meantime, no one seemed to care that none of Colt's competitors were doing any of these things, and they slowly started dropping all of these features, starting with the sear block, which they simply replaced by what today is colloquially termed a "sear web," that is to say, simply an incomplete machining of the DIAS pocket in the lower receiver, cheaper and easier than sourcing and blind pinning steel sear blocks.

This was followed in approximately 2005, when they switched to standard weight bolt carriers, and 2009 by standard FCG pin dimensions.  Today's Colts have no unusual parts save for the sear-web, and are fully interchangeable with select-fire variants except for the auto-sear components which would require machining on any currently produced "AR15" lower, high or low shelf, which refers not to a standard auto-sear, but to compatibility with a DIAS.

~Augee