I just took possession of my 1st M16, a Frankford Arsenal conversion of an Oly receiver. I've taken it out 2 times and unfortunately I'm having problems with it.  Basically, it's a jam-o-matic!  I'm hoping someone can give some help and advice.  Here's my saga:

Each time I took it out, it ran fine for the first 2 mags. Then the jams started happening and wouldn't stop. It almost seems like the gun runs fine when cold, but after it heats up it jams constantly. (I'm in Phoenix so after the gun heats up, it stays hot for the rest of the afternoon!)

The jams appear to be the classic "fail to eject" type.  The spent case gets completely extracted from the chamber but does not get ejected from the action.  The jam occurs with the carrier pushing an empty case and a live round forward at the same time.  It does this whether I try double-taps or "empty-the-whole-mag" full auto blasts.  Semi-auto firing seems to work with the weapon cold, but today with everything hot, even semi-auto was causing jams.  Note: With the gun cold and functioning, the spent cases get ejected a good 5 feet away which is what I would expect, i.e. they are not just barely making it out the ejection port.

The ammo used was PMP "gazelle" box and Federal XM193 -- both jammed the same.  My mags are all USGI 30-round with new springs (red extra power) and green followers.  These mags have worked 100% in my SP1.  Just for kicks, I also tried a couple 20-round Colt mags (with old springs), and they jammed on every round.

The jams remained consistent in switching between a Bushmaster M4 upper and a Colt M4 upper.  I used the same bolt and carrier however.

I've cleaned the bolt & carrier and visually inspected the extractor and ejector and can find nothing obviously wrong.  The ejector spring is stiff, just like the one in my SP1. This doesn't mean they aren't defective of course.  This gun has had a ton of rounds through it, so it's possible some of the parts could be worn out.

So my questions are this:

1) If it is extractor/ejector related, can I try putting in the bolt from my SP1? (with the full auto carrier of course)  Or should I buy a new bolt?  If so, what brand should I get?  I have no idea who made the carrier, should I stick with Colt or Bushmaster for the bolt?

2)  Is it possible that the recoil spring and buffer are "too weak" and the carrier is cycling and coming forward too fast and not giving the spent round enough time to clear out of the ejection port?  I know this sounds crazy but I thought I'd ask anyway.

3)  Any ideas why this only happens when the gun heats up after 2 mags?  It seems like a mechanical problem should be there whether hot or cold.  Color me confused.

Thanks in advance for any help!

Whose barrel?

Tried two uppers:  (1) Bushmaster upper receiver with Bushmaster M4 14.5" 1/9 5.56 barrel w/ Phantom FS, and (2) Colt upper with Colt M4 14.5" 1/7 5.56 barrel w/ A2 birdcage FS.

Jams the same with either upper (using same bolt & carrier).

Has the headspace been checked?

No.  I got the BM upper assembly straight from BM, so I assumed it was headspaced at the factory.  I've fired several hundred rounds through it on my SP1 with no problems.  Regarding the Colt upper, it came with the M16 and I have no knowledge of its history.  I assume it's been headspaced because (supposedly) the gun ran fine with it, of course this might be a faulty assumption.  Unfortunately I have no headspace gauges so I can't check (maybe that should be on my list of things to buy).

Also forgot to mention above that the carrier always locks open on empty, so this would seem to rule out a short-stroking problem.

If this is indeed what is happening, then it's one of two things or both.  

The first is a week ejector spring.  Replace this.

The second is a week extractor spring and/or a broken extractor (look around the lip of the extractor).



Both of these conditions will re-occur no matter what upper if you use the same carrier group.

A simple check is to replace the bolt and see if that helps.  You can try the SP1 bolt just to check function, but it doesn't hurt to buy new bolts.  I prefer Bushmaster...just my preference.

The heat is probably making the springs weaker as they get hotter, thus the malfunctions after two mags.

Which upper did the bolt come with? How is the carrier and bolt marked? Are you using a full stock or a collapsible? Are you seeing a stong extraction mark on the extractor rim like the one pictured here?

[url]http://ar15.com/forums/topic.html?b=3&f=66&t=169185[/url]

The extractor and ejector have a synergistic relationship. If the extractor is weak it may manifest as a FtEj. What does your extractor spring look like? Compare it to the one in your SP1. Carbines have to use stronger extractor springs than rifles.

The bolt, carrier, and lower receiver came with the Colt upper.  I put my BM upper on because I wanted a flat-top.  The carrier has a single "C" on the side, and the bolt has "CMP" on it (I think -- the letters are pretty worn).  Looking at the fired cases, I see what looks like an extraction scrape on the rim, although it's inconsistent and sometimes hard to see.

As far as the stock, it's the collapsible type.  I looked at the telestock buffer and spring and they look exactly like the ones from my SP1 carbine -- the springs are exactly the same length.  I looked in the BM catalog and noticed that there is a heavy weight telestock buffer for the M16-M4, marked with an "H" in the picture.  My buffer has no such markings, making me believe it is the standard telestock buffer.  Could this be part of my problem?



I neglected to mention above that my SP1 is the carbine version (all original).  I compared the extractor springs and they look similar with both having the blue base.

I'm wondering if using the wrong buffer is related.  Before I took possession, the gun had some kind of hydraulic heavy buffer.  The owner said it was to slow down the rate, although it gave the side-effect of not locking open on empty.  I wanted it to always lock open on empty, so I asked him to put in the stock buffer.  He didn't have the original, so maybe he put in the one for a semi-auto carbine.  I'm thinking maybe I should get a new bolt and heavy buffer.

Those are Colt parts. For the sake of brevity lets put the Colt carrier assembly back into the Colt upper.



In a carbine with the correct weight extractor spring the marks are pretty obvious.



Yes, with an FA carbine and 14.5" barrel you'll need the "H" buffer. It helps with bolt carrier bounce and the resultant light firing pin strikes.



You'll need an extractor spring with a black insert. Make sure to buy it from a Colt dealer so that you'll know it's not just a rifle spring with a black insert.



Before you change bolts buy headspace gages. Try swapping new extractor (black insert) and ejector springs. There's a spare ejector spring disguised as a selector spring in your Colt carbine. You can use the ejector spring from the Colt bolt as a selector spring in your Colt carbine.

You may want to add a Colt collapsible stock to the list too if the stocke on the OAI receiver is one of theirs.

Thanks to Tweak and frisco for the great advice, it's greatly appreciated.

I'll try to locate a Colt extractor with black insert around town -- maybe I'll give Ken at SAW a call tomorrow.  Unfortunately his shop is way on the other side of town from me.  Anyone know another source for Colt parts in Phoenix?

I'm not sure of the maker of my collapsible stock -- I can't find any markings on it.

Again, thanks for the help!

Chessman.

Give SAW a shot, even tho it's across town. Tell Ken you're there compliments of ARF. [:D]

A Colt collapsible will have an "N" on the right side of the stock underneath the side of the latch, forward of the latch pin.

[img]http://photos.ar15.com/WS_Content/ImageGallery/Attachments/DownloadAttach.asp?sAccountUnq=12467&iGalleryUnq=934&iImageUnq=17349[/img]

I learn something new every day!  Yes, it's a Colt.

[b]Problem solved![/b]

I took my M16 out to the range today.  I had a couple friends show up with their M16s and spare parts.  With a bunch of spare parts among 3 M16s, we figured we would be able to get it running one way or another!

First I put in an H-buffer in the stock.  First mag fired fine, but second mag started the same FTE errors as before.

Next I swapped in a different extractor with extra-power spring (used my same Colt bolt and carrier).  Problem solved!  She ran like a champ after that.

I put about 300 rounds through it, using a variety of 30-round mags (loaded some to 28 rds, some to 30 rds) and a 20-round mag.  Used South African PMP ammo.  Did lots of double-taps, controlled bursts, and full mag dumps.

It ran 100%.

Thanks again for the help!

Thanks for posting your fix.  Lot's of people post problems but few bother to post their solutions.

thanks!