ok.  got this M16 that used to work all the time with no problems.  recently, during a shoot, the thing starts failing to extract occasionally.  leaving an empty shell in the chamber.  first, i changed the gas rings and cam pin and extractor and extractor spring.  then i changed the entire bolt after it kept doing it.  then i changed the buffer spring.  upon inspecting the brass, it is evident that the extractor claw is ripping a bit of brass off the base of the ammo, as if it is not totally engaging the lip of the case.  i put another upper on the gun and it runs fine.  back to the original upper and the same thing happens.  basically, i've changed out everything except the barrel.  could the barrel be the problem?  it's about the only thing not swapped out for new parts so far....

TIA for any suggestions !!!!

Sounds like you may have a dirty chamber.
The casings are getting stuck and the extractor is pulling off of it.

Soak the barrel chamber in CLP, then spin a CLP soaked 30 Cal cotton cleaning mop (mounted on a few sections of rods, spin in a drill) in the chamber in an in/out motion.  This will get the crud/fouling out of the end of chamber (last cut before the throat) that you may be missing during cleaning.

Once you have the chamber fully clean, check the finish on the chamber walls.  If the barrel/upper was shot in a sandy environment,  sand/dirt may have gotten in the chamber on the ammo cases and scuffed up the chamber walls.  If this is the cause, then you will need to polish out the chamber. Same method as cleaning, but using bore brite or another fine grit polishing compound on the mop.  The one thing to remember during polishing is that you are trying to just get the chamber walls to shine, not trying to enlarge the chamber in any way.  This means that you do not shove the mop into the barrel (rifling), just the chamber before the throat of the rifling.

good suggestion guys.  actually, i did a thorough cleaning of the chamber, including a polishing prior to testing it out today.  same problem persists.  this one really has me stumped.  i'm going to swap barrels out and see if that helps.  

TIA  ~~ !!

I was having similar trouble on a brand new 16" upper I got from BMI.  A heavy duty extractor spring with the black insert I got from SAW locally fixed my troubles.

Could your gas port have opened up due to high rates of fire?  Too much gas could result in torn rims.  Or possibly the headspace has increased to the point that the extractor can not get a good grip on the cartridge case any more.  Then again, if you put a new bolt in, you would think that would solve the headspace issue if that is the problem.  Do you have an approximate guess on the number of rounds through this barrel?

What ammo are you shooting? If it is reloads the pressure curve maybe to high due to type of powder (voiding gas timing)

Pull the bolt and place a fired case in the bolt face engaging the extractor, look and see if you are getting a full engagement of the extractor in the groove of the case, then pull.

PS.
Use a dentail pick and make sure the extractor is cleaned out be hind the claw.

Frist guess;
1) weak spring
2) worn extractor
3) both

I'd say the gun only has about 3000-4000 rounds thru the barrel.  too much gas?  i dont really know what you mean by that Jason_h, but when i replaced the bolt, it still had the same problem.  When i replaced the entire upper with an M4, it ran fine, that is why i suspect the chamber and/or a barrel problem. i'm going to replace the barrel and gas tube today, and hopefully can get out next week sometime to test it again.  

ammo - was shooing South African 5.56, which runs 100% in my M4.  The rifle in question and the one having the problem is a full size 20 inch gun.  also tried running it with IMI SS109 ammo and had the same problem.  

on the surface and first guess, was the extractor and/or extractor spring right?  well, when i replaced both it still did had the same problem.  then when i replaced the entire bolt, it still had the same problem, that is why i suspect the barrel and/or chamber area. i think i do have a wolf (?) heavy duty extractor spring somewhere in my tool kit.  that might be the ticket also....

oh well----eventually we'll figure it out.  

last week at my dept, we had a new glock 45 that jammed quite frequently.  we had 6 guys, all glock armorers looking at it and taking it apart and replacing parts.  to make a long story short, we eventually ended up replaceing every single part less the slide, frame, and barrel --- but it works now !

go figure !

Thanks for the inputs.  i'll keep you posted...

Ok guys,
Just short of using voodoo and sacrificing a goat, your current attack plan is not going to work to fix the rifle.

The facts are that the rifle ran for 3-4K rounds, and then started to have problems.  The case is sticking in the chamber, with enough force to allow the extractor to bend the rim of the case before it lets loose.
Point blank, the rifle is showing signs of ammo overpressure, This is either being caused by the end of chamber not being clean and crimping the case end on ignition, or the chamber is rough (polished wrong) and the cases are being friction retained to the point that they can not be pulled from the rifle under barrel pressure (will manually eject after the barrel pressure has bleed off).

Here is the attack plan:

1.Pull the barrel off the rifle.  This will allow you to work on the barrel, and get to all the parts that need attention.

2.Using acetone, clean the chamber to make sure that there is no sealant clogged in the chamber at the last cut. Use a pick if you have to, but make sure that the end of chamber cut is clean.

3.Using a Q-tip and acetone, clean the inside of  barrel extension lugs.  Again, there may be bullet sealant and a piece of debris stuck in the lugs that is slowing unlock of the bolt and making the rifle have signs of overpressure loads.

4.Using a light, check the surface of the chamber (still dry due to the acetone).  Make sure that it is smooth as a baby’s ass and gleaming with no tooling marks/grooves present.  Also, check to make sure that the chrome plating is not chipping or flaking off.  A bad polishing job will burn threw the chrome plating and/or groove the chamber surface. Another thing is if the chamber was polished with the barrel still in the upper, it may have oblonged the chamber with the plating burned away on one of the sides.



[B]As for this:[/B]



Hate to be rude, but you had six monkeys fucking a football.  There is no reason that every part on a pistol needs to be replaced to solve a single problem.

As a smith, step one is to know what the problem is, then the next step is to fix the single problem, not change out every part until you stumble across a fix.  These are not smiths, but part changers. I can just image the bill if anyone of these guys were smiting in the private sector.  

I guess it just boils down the differences of being a Smith, and being Armor.  Looks like if anyone every calls me an armor, I should just take that as a insult, and sucker punch them dead in their face!!!!!


P.S. Just to let you guys know, I have to go to the dentist in a few hours for a root channel.  This might explain why I am a currently a little temperamental on this post.

good points dano.  and yeah, i had a root canal last year so i know how it feels....

"The case is sticking in the chamber, with enough force to allow the extractor to bend the rim of the case before it lets loose."

i agree ---

took the barrel off the gun as you suggested and the chamber is in bad shape in my opinion.  after cleaning it to the best of my ability, it looks as if the chrome plating is coming off and the chamber is very very rough, almost with groove marks in a circumfrential direction down the length of it.  i thought about trying to polish it out, but opted to change barrels instead at this point.  if i have the energy, i'll attempt to get out tomorrow and test fire for a few hundred rounds to see how it does.  i believe this is an older FN barrel, but do not know when or where it was picked up.

and the rest of the story......

i found out the chamber area of this gun has never been cleaned by the owner.  he did not know what a chamber brush was, much yet how to use it.  found out he did clean the gun after each shooting, but only ran a brush down the BORE of the barrel, never touching the chamber.  now, my guess is that if it truly is 3-4k rounds, that might wear out a chamber and at least make it rough.  perhaps there might be more rounds thru it, but that is an unknown.  it makes sense to me that if it was never cleaned, there would be a lot of buildup of crud that would continue to grind itself into and onto the chamber every time it is fired, ultimately wearing it out prematurly.  i have given him a chamber brush, and if the gun works now, he'll be on his way hopefully to know how to clean the rifle....now since the owner is a family relative, i wont divulge his identity to save him some embarrasment.....

CampyBob has a PMDS M-4 with over 14k rounds on it and I doubt if it has ever seen a chamber brush.  He says it still runs fine!

IIRC DPMS chromed some FNMI unfinished barrels.

I wonder if that could be the problem.

Burnsome,

Any markings on your barrel?

yes sir

the barrel markings are:

E MP 5.56 NATO 1/7

Argh, I wish you would have said that right off.

[url=http://www.ar15.com/forums/topic.html?b=3&f=12&t=153649]Beware, E marked Barrels [/url]

[url=http://ar15.com/forums/topic.html?b=3&f=12&t=160616]Barrel Markings: P MP 5.56 NATO 1/7 [/url]

Last [url=http://safety.army.mil/pages/media/pubs/cm/cmnov2001.doc]nail[/url] in the "E" barrel coffin.

wow - thanks all !

just to close this one out, i thought i'd provide some feedback from the range date today.  new barrel installed and the gun ran fine.  no problems whatsoever.  now, i'm wondering if the original manufactuer would replace this barrel if i contacted them and explained the situation...???....

i guess i'll drop them a line and see what they say...

thanks all for the help.  nothing like tapping into the "body of knowledge" that exisits on AR-15.com