Old Colt SP1 and Full Auto FCG???

[supersonic]

In the #3 position, the only thing that holds back the hammer in a proper Fully Automatic AR-15/M16 is the Auto Sear. The design of the selector is such that when it is turned into the 3rd position, it pushes down the back of the disconnector, disengaging it from the backside of the hammer when it is pushed back by the carrier. The reason it does not slamfire is because the carrier is not a full auto carrier: It is the Colt SP1 carrier, so it should not allow for full auto or slam fire type situations. Furthermore, what vexes me is why the carrier was not allowed to go forward after charging it when in the 3rd position. Maybe with the sear notch on the hammer, it is jamming up on the carrier when it is coming back forward towards battery??? Without the auto sear holding the hammer back, im thinking the problem lies in the semi carrier. Wonder what would happen with a full auto carrier??? I sure ain't finding out....

Now that I have had time to go back and read this, I have to say that I really want to hear your explanation of your words that I highlighted. What does the BCG type have to do at all with whether or not an AR without an AS will go into F/A or slam fire? Do you know where the auto sear engagement notch even is in relation to the bottom of the carrier when it is going forward into battery? And, since there is no auto sear to catch the hammer to begin with, the hammer will just follow the carrier home, not get caught up on the notch.

[DesertGunner]

It is not a defense that "it came that way from the factory." Remember that case in Wisconsin that Lou Dobbs was publicizing? Army Reservists lent an AR to a friend, it was an old Olympic Arms with FA FCG. It doubled at the range, cop witnessed and contacted ATF, owner convicted of illegal transfer of MG. I wouldn't go near that thing w/o a semi FCG and a pin punch.

Except that's not even close to what actually happened....

[supersonic]

I have an SP1 that came from the factory in nearly the exact configuration you describe. Mine had a FA BCG

Are you absolutely sure about that? The Colt SP-1 Model AR-15 had its own SP-1 Bolt Carrier which was absolutely semi-auto. In other words, it came with an SP-1 AR-15 carrier, not an M-16 carrier, which is what is considered a "Full Auto Bolt Carrier." Here are the differences:



The one on top is an AR-15 bolt carrier (semi-auto)
The one in the middle is a Colt SP-1 bolt carrier (semi-auto)
The one on the bottom is an M-16 bolt carrier (full-auto) ***Notice the firing pin shroud on this one***

[FLIGHT762]

Are you absolutely sure about that? The Colt SP-1 Model AR-15 had its own SP-1 Bolt Carrier which was absolutely semi-auto. In other words, it came with an SP-1 AR-15 carrier, not an M-16 carrier, which is what is considered a "Full Auto Bolt Carrier." Here are the differences:



The one on top is an AR-15 bolt carrier (semi-auto)
The one in the middle is a Colt SP-1 bolt carrier (semi-auto)
The one on the bottom is an M-16 bolt carrier (full-auto) ***Notice the firing pin shroud on this one***

This discussion perked my interest since I have owned several early SP1 AR-15's over the years. I looked at my earliest example which is a early gun, A SP1 with serial # SP095XX (yes, four digit under 10,000) This rifle was purchased by me in the early 70's from a Viet Nam Vet who bought it after returning home in the late 60's. It has the old style 3 prong flash hider. The BCG is similar to the two AR-15 examples above that have the bottom of the BC milled off, except the firing pin area is enclosed like the M-16, not milled out like the 2 AR-15 examples. The BC is such an early example that it has smooth sides to it and does not have the forward assist notches milled into it (pre M-16 A1).

The FCG is standard two position, SAFE and FIRE and does not rotate to the third position. None of my SP1's rotated to a third position. It is my opinion that the rifle mentioned by the O/P had a full auto selector installed. It did not come that way from the factory.

[goodlookin1]

Now that I have had time to go back and read this, I have to say that I really want to hear your explanation of your words that I highlighted. What does the BCG type have to do at all with whether or not an AR without an AS will go into F/A or slam fire? Do you know where the auto sear engagement notch even is in relation to the bottom of the carrier when it is going forward into battery? And, since there is no auto sear to catch the hammer to begin with, the hammer will just follow the carrier home, not get caught up on the notch.

I totally get what you're saying. And I agree. I was really just thinking out loud. I couldnt think of what else it could possibly be: I mean, what else could possibly get in the way of the carrier returning to batter other than the hammer? I guess the only other possibility is that, somehow, the hammer wasnt itself the problem but rather something in the way the FCG was acting, in that it kept the hammer from following the carrier when returning to batter.....ergo holding up the BCG.

As for the non-slam fire, the whole reason that a semi carrier has that notch cut out underneath the firing pin is so that the hammer WILL hit it. If you think about the direction the hammer would be hitting the firing pin at the half way point of the carrier return, it is hitting the firing pin upwards, probably at a 45 degree angle....not perpendicularly which is needed to dent the primer. However, when you have that extra metal there to keep the hammer from hitting the firing pin until the carrier and bolt is fully into battery, that extra metal is acting like a piece of leverage, enabling the hammer to potentially strike the primer in the perpendicular position needed to ignite the primer. Again, just thinking out loud on this one....im not what I would call an AR-15 guru, but I know my way around the block

[goodlookin1]

PICTURES!!!

[goodlookin1]

[FLIGHT762]

I forgot to mention, my early rifle has a hammer that is rounded, similar to the m-16 except the auto sear hook on the rear has been removed.

Photos of your later rifle came with a hammer that had no hook and had a notch cut out in the front of it.

Your rifle photos has an M-16 hammer installed.

My early rifle has no chromed chamber or bore. Your rifle should have a chromed chamber. Much later rifles had chromed chambers and bores.

[desertdweller]

Very nice! A real keeper.

The picture of the inside definitely has the extra aluminum to block the auto sear.

[AJAX22]

My spidy sense is going off like an alarm....

That is not the original carrier... which means that things have been replaced internally....

something is not right.

[freonr22]

gorgeous! Ballzy too

[Ron-Solo]

The hammer, selector and disconector appear to be F/A parts. You can see the extra tail on the disconnector where it goes under the selector switch.

Someone has changed some parts.

Easily fixed, but dangerous ground the way it is.

[redcliff]

I was quite familiar with SP1's back in the day (early70's) and never ran across one that came stock with full auto fcg's. Perhaps they're out there but I've never seen one.

[goodlookin1]

Guys....

I want to make clear, VERY CLEAR, that this IS NOT my rifle. This rifle is located out of state and not owned by me or any family.

My spidy sense is going off like an alarm....

That is not the original carrier... which means that things have been replaced internally....

something is not right.

Hmm....well I suppose it could have been changed them out initially, but it definitely wasnt by the current owner: He's had it for a LOONNGG time sitting in a safe. Out of curiosity, what makes you think the carrier is not original? Looks like the SP1 to me. If it is different, it **could** also mean that the original carrier broke or something happened to it and had to be replaced; doesnt necessarily mean that this rifle didnt come this way.........but it would be suspect.

Do you happen to know what year this was made by the serial #?


The owner is gonna flip out when I tell him that this thing is a felony waiting to happen. He'll probably want to be rid of the thing! He doesnt know the first thing about changing out a FCG.

[AJAX22]

The carrier is from a later model, (note the cuts in the side for a forward assist)

It's a proper SP1 type carrier ground from an m16 bolt, but it's not correct for that upper.

The thing is, if it's early enough to have the m16 FCG then it shouldnt have a later model bolt carrier.

And since there is almost NO wear on the FCG, it's hard to explain away by 'it wore out'

I'm not saying it didn't happen (some of the early slick side carriers were chrome and some people didn't like the glint while they were out hunting etc. So it could have been swapped out for cosmetic reasons...

But it does set off my 'not quite right' detector.

You definitely can determine year by serial number, I'll look it up when I'm in front of a computer.