FA FCG in SA lower

[kajen]

this is not a question on making any gun fullauto

what i need to know is i have a FA FCG w/o autosear and a lower milled for SA(as in no room for sear etc)
can i install the FA FCG in the SA lower and just run normally and what will happen if selector is set on FA? will the disconnector catch the hammer as usual and just work as semi or will it cause some malfunction?

[Eurodriver]

this is not a question on making any gun fullauto

what i need to know is i have a FA FCG w/o autosear and a lower milled for SA(as in no room for sear etc)
can i install the FA FCG in the SA lower and just run normally and what will happen if selector is set on FA? will the disconnector catch the hammer as usual and just work as semi or will it cause some malfunction?

They make three position AR15 selectors Safe/Fire/Safe if you want the ability to flip the switch to that happy position legally.

[kajen]

hey thanks for the answer

its not a legality thing since im not in the US so US Fa laws dont apply

but i want to assemble an ar today for some nightshooting with some friends tonight ..

but i only have semi lowers and fullauto FCG so the question is will it work as a normal semi fcg or will it malfunction if it ends up in the sprayandpray position

my thought is that w/o the autosear the disconnector will catch the hammer as it does in semipos. i might be wrong?

[QuietShootr]

hey thanks for the answer

its not a legality thing since im not in the US so US Fa laws dont apply

but i want to assemble an ar today for some nightshooting with some friends tonight ..

but i only have semi lowers and fullauto FCG so the question is will it work as a normal semi fcg or will it malfunction if it ends up in the sprayandpray position

my thought is that w/o the autosear the disconnector will catch the hammer as it does in semipos. i might be wrong?

No, the hammer will follow the bolt down, which may pop off an extra shot or two but more likely will just cause a malfunction. ETA: it will work fine in semi.

[GTifosi]

In semi, the disconnect catches the hammer.

In FA the disconnect tail is shoved down by the selector lever which takes it completely out of the picture.
At the same time the auto sear rotates into a position that allows it to catch the hook on the outer tail of the hammer where its held back til the carrier coming into battery releases it to fire the next round.
(or its caught by the trigger if its been released thus stopping the fire cycle until the next trigger pull)

If you've a FA FCG -sear you may inadverantly end up with a slam fire situation depending on a few variables.

Now if the tail of the disconnect were ground off to give it a shape like a SA disconnect, the would be nothing for the selector to engage and move and as such should only allow fire in a SA fashion.
(even if the auto sear was present and functional. with trigger held sear would catch hammer, BCG would release hammer when coming forward. From there the disconnect would catch hammer if the trigger was held down, or the trigger proper would if its released)

Basically you'd end up with 'safe' 'semi' 'semi' as selections.

You can see the tail that needs to go. Or just try to obtain an actual SA diconnect.
http://www.ar15.com/content/legal/ar15-m16parts/disconnector.gif

[kajen]

thanK you!! that cleared it up 100%

its just a temporary solution for tonight but i will file it down ..

thanks again

[Iraqgunz]

If you install a real fire control group (hammer, trigger, disconnector, selector lever, etc...) minus the auto sear your weapon will fire more than one round. In fact it will fire like a machine gun.

One thing that can affect this is the type of ammo and primers.

[GTifosi]

Removing the disconnector tail prevents that by allowing it to engage regardless of selector being in semi or auto postion.

I do contest the 'firing like a machinegun' part though.
Countless people have removed thier SA disconnector, which creates the same outcome as sear removal; a free flying hammer, in an effort to achive just that effect and found they were wasting thier time and effort.

Certainly primers have much to do with it, as do a few other things but in general the odds are pretty slim that a slamfire FA will be created.

Kids: don't try it at home.
Its illegal unless one has certain special licences and conditions and will net you some time with bubba the butt humper if you don't.

[QuietShootr]

If you install a real fire control group (hammer, trigger, disconnector, selector lever, etc...) minus the auto sear your weapon will fire more than one round. In fact it will fire like a machine gun.

One thing that can affect this is the type of ammo and primers.

That was what I was addressing with my post. As you know it's a hammer following situation as opposed to a properly timed sear release. IME (at a licensed manufacturer, of course) this will not reliably fire automatically, though it's good enough to get you in trouble with the law if that is applicable. Using soft pistol primers is ATF's favorite trick to get a hammer-following gun to fire more than one round for purposes of prosecution.

Anyway - It won't work well, was my point.

[Iraqgunz]

I did some testing on this subject and was able to successfully fire several 30 round magazines on full auto. The suppressor seemed to assist in facilitating it.

I believe some of the ammo was PMC Bronze Line and some handloads.


That was what I was addressing with my post. As you know it's a hammer following situation as opposed to a properly timed sear release. IME (at a licensed manufacturer, of course) this will not reliably fire automatically, though it's good enough to get you in trouble with the law if that is applicable. Using soft pistol primers is ATF's favorite trick to get a hammer-following gun to fire more than one round for purposes of prosecution.

Anyway - It won't work well, was my point.

[Iraqgunz]

I did in fact conduct testing on this matter and have video showing a 30 round mag dump in under 4 seconds.


Removing the disconnector tail prevents that by allowing it to engage regardless of selector being in semi or auto postion.

I do contest the 'firing like a machinegun' part though.
Countless people have removed thier SA disconnector, which creates the same outcome as sear removal; a free flying hammer, in an effort to achive just that effect and found they were wasting thier time and effort.

Certainly primers have much to do with it, as do a few other things but in general the odds are pretty slim that a slamfire FA will be created.

Kids: don't try it at home.
Its illegal unless one has certain special licences and conditions and will net you some time with bubba the butt humper if you don't.

[GTifosi]

I didn't say impossible, I said pretty slim odds.

Nor do I contest that you accomplished it. (in fact I'd go so far as to say I'd be more surprised if you hadn't)
I contest that its nowhere near as easy as it sounds.

Most folks don't have access to a supressor and home rolled cartridges which can skew results. (PMC Bronze notwithstanding)

Tweaking springs and carrier weight can help too though that is not something most folks have a lot of laying around to optimize with.

Again, definitely not impossible, but odds of failure are significantly higher than odds of success.

If it were really that easy there'd be a great many more people out there who got *busted for removing thier disconnect, grinding the hammer engagement hook, or even just tying it back with a bread tie to make a bullet hose.

*Because you know there's a pile of dumbasses who have to try it at least once.
On a public range.
In front of people.
With a camera and youtube vid to show off with
;)

[QuietShootr]

I did some testing on this subject and was able to successfully fire several 30 round magazines on full auto. The suppressor seemed to assist in facilitating it.

I believe some of the ammo was PMC Bronze Line and some handloads.

I bet that probably did help. Wonder if the increased carrier speed allowed the hammer to lag behind it enough to make it work? Or does the increased speed only happen on the rearward stroke?

[warpigM-4]

you could always Mod the parts:D to semi cut the hammer tab and the disconnector would it not run semi only then with No hang ups:confused:.
a Bubba Home gunsmith/dealer did this in the 80's and early 90's that I knew .
he could get FA parts cheaper with surplus purchases he did .He would file the hammers and Disconnectors .

although I believe he did use semi selector switches ,I do Know the ATF came down on him for some other things he was doing with unregistered RDIAS (he was making them) .But lucky for you the ATF does not factor in on this .

[GTifosi]

I bet that probably did help. Wonder if the increased carrier speed allowed the hammer to lag behind it enough to make it work? Or does the increased speed only happen on the rearward stroke?

Faster movement rearward should give more buffer spring compression as it tries to slow, stop, and reverse direction of the BCG.

More compression/stored energy pushing the BCG forward should mean more velocity too.

At least as I grasp it anyway.

[QuietShootr]

Faster movement rearward should give more buffer spring compression as it tries to slow, stop, and reverse direction of the BCG.

More compression/stored energy pushing the BCG forward should mean more velocity too.

At least as I grasp it anyway.

I could see that, or I could see that since the length of the stroke is the same, the compression velocity doesn't matter. Is there a physicist in the house?

[Clem]

Since someone asked regarding the Potential Energy stored in a spring.
This website explains it pretty clearly. It'd be harder to type the formulas.

http://theory.uwinnipeg.ca/physics/work/node5.html

To answer your question. If the spring compresses the same distance, then no. Potential Energy stored in the spring is the same no matter how fast it was compressed.
But if the bcg is travelling faster, it'll most likely compress the spring more than if the bcg were travelling slower.
Although, if the spring is already compressed to the max, then the original statement holds true.
Hope I wasn't too confusing in my explanation.

[GTifosi]

Potential rebound of the buffer if it bottoms in the receiver extension and how hard as a result of carrier speed may play into too.

Way overthinking it by now, ain't we...

[ClearedHot]

Without an auto sear in place if you tried to shoot with the selector on Auto, wouldn't the weapon fire the entire magazine even if you took your finger off the trigger?

[GTifosi]

No.
The released trigger would catch and stop the hammer.