m16 function mystery HELP!

[hktome]

hoping the files can come through, I am stumped , :we have a SP-1 converted to a pinned in G.I. type auto sear, and it worked just fine with its bushmaster 11 1/2" hbar with and without a suppressor for several years, and then all of a sudden it starts failing in full auto working only in semi, so we cleaned the gas key, the barrel, and even swapped the gas block out to larue low pofile , and upgraded the upper to a CMT flattop, still no go, decided to put the upper on another lower -it worked!, its the lower right? no! the lower seemed fine with another upper a 7.5" dmps kitt kat we have changed the hammer spring, the sear and sear spring,the disconnector and spring...any ideas?the only difference in lowers we could observe as the troubled unit has the sear spring tensioning leg foward of the selector switch and the other-which worked has the springs leg behind the selector, both seemed equal in tension, I am stumped what the WECSOGers here??thanks in advance!! P.S. can a barrel "go bad"?

[TheOtherChris]

For the sake of discussion, I am going to assume this lower is properly registered/possessed per NFA regs.

Is the FCG a SAFE, SEMI, FULL or SAFE, SEMI, BURST (with the ratchet) or one of those funky 4 position ones?
When you say that it fails in FULL, are you saying that when the selector is set to FULL, the rifle functions semi; so that your selector effectively functions SAFE, SEMI, SEMI?

Have you tried just swapping carrier assemblies and not the entire upper?
Is the sear pin tight in the lower or is the hole worn?

If it functions correctly in SEMI, it is unlikely to be the gas system, but rather a mechanical issue.

Have you tried a function test?
With the 'problem' lower and upper assembled (NOT LOADED) set the selector to FULL, pull and hold trigger, then while holding trigger pull charging handle to retract carrier and SLOWLY ease the carrier forward (use forward assist if needed) until it contacts the safety sear and you hear the hammer fall again.

[mhg]

Do you have the correct carrier in the problem upper?

It's acting like it has a AR15 carrier.


Matt

[hktome]

the fire conrols are M16A1 type safe-semi -fullauto, and yes this gun is a post 86 dealer sample converted years ago by Bill Fleming the trigger and hammer pin holes have worn enough that the owner has replaced the pins with longer units that have e-clips on the ends to prevent walk-out and although possible, wear on the auto sear holes is not readily evident and yes it is for sure a 16 bolt carrier thank you for the input guys I will see about measuring the auto sear pin hole diameter

[1811GNR]

I can't help with the malfs but you might want to get a set of the KNS anti-rotation hammer,trigger pins. Keep things aligned and prevent future wear. They make one for the sear pin too.

[Court in Fl]

I have an AR that was converted back in 1983 and I had trouble with the hammer in full auto droping on a live round and not setting it off.

Worked great in semi.

The timing was off by about .010.

I worked on the GI auto sear so it would trip a little later in the cycle and it has run like a raped ape ever since.

Check your buffer also, make sure your not getting any bolt bounce.

If the hole for the sear has worn out of spec the hammer could be dropping to soon, or maybe not at all.

Is the machine gun jaming or is there a live round in the chamber and it's just not going off ?

Court in FL.

[chromestarhustler]

i might be wrong but i didnt think kansas allowed full auto, in fact i am almost postive since i live here and attempted to get on on several occasions. unless the owner is a class 3 dealer in that case the gun should probably be sent off to a specailist. if the holes were worn out why werent they bushed.

[TheOtherChris]

Originally posted by hktome
the fire conrols are M16A1 type safe-semi -fullauto, and yes this gun is a post 86 dealer sample converted years ago by Bill Fleming the trigger and hammer pin holes have worn enough that the owner has replaced the pins with longer units that have e-clips on the ends to prevent walk-out and although possible, wear on the auto sear holes is not readily evident and yes it is for sure a 16 bolt carrier thank you for the input guys I will see about measuring the auto sear pin hole diameter

Have you tried using the problem upper/lower with an M16 carrier from a different rifle?
Did you try the function test with the problem upper/lower?
That may at least allow you to see the problem.

As Court mentioned: Timing is everything.
If the safety sear is bent or worn, or the pin holes are worn, it might prevent release.

[hktome]

court in fl., the other chris, I really think you have idenified the problem, we had changed the sear out but did not really look at the sear pin hole condition, we will try to take a measurment of the hole and determine if its wobbled out , and I would not be surprised if it is, just for good measure, how does one check buffer bounce?, (we have also changed buffer and spring by the way) I knew this board would rise to the challenge and help out!!

[Court in Fl]

The way I changed the timing on mine was to put a little bend in the auto sear.
I had to heat it up till it was red to get it to bend (very hard metal).

On my gun the hammer will drop just as the carrier closes all the way.

You can also thin the sear where the carrier hits the back of it to make the hammer fall later.

You may want to see how much play you have in the trigger and hammer holes
as this could be a factor also.

You could turn a set of custom pins a few thousands bigger and grind the holes in the trigger, disconnector and hammer so the new pins are a good fit.

The diamond tipped Dremal bits work real good for this.
I have made sets of M16 fire control parts for use with the large Colt pins this way.

Good luck, Let us know if you get it working.

At least it's a dealer sample and not a $10,000.00 gun.

how does one check buffer bounce ?

Make sure your buffer has the moving weights in it.

Court in FL.