Trying to make a long story short, I bought this barrel assembly in 2014: https://www.aimsurplus.com/product.aspx?item=XATIB556M4BNDEC and after installing it (recently) on a PSA upper receiver but before shooting it, I came across some comments in threads on ar15.com (http://www.m4carbine.net/showthread.php?134302-Critical-Failure-Seeking-Advice/page9) and some other sites where people mentioned the chamber was too tight and was not 5.56. Because of what I read I bought the Michiguns chamber gauge to test it for myself. No surprise, I had the same issue as others. I also did some other tests with some .223 ammo loading it in a magazine cycling the ammunition pulling the charging handle back and dropping the bolt carrier group repeatedly. All of the .223 ammo cycled and ejected just fine whereas the 5.56 ammo failed to extract and was stuck with the next round jamming into the stuck round. I also just hand inserted a .223 round into the chamber and then tilted the upper back and it dropped out freely. Doing the same thing with 5.56 I had to pound the upper down on my floor. I contacted ATI customer service with lots of information as well as sending the links and comments I had found. After some back and fourth, their final response was, "Hello you can go ahead and use it if anything happens to it using the correct ammo we can bring it in under a return authorization. The gunsmith would be able to determine by looking at a damaged barrel what caused the damage so at that point management would have to make the final decision. Either way us it should be fine."

Here is my question, should I go fire it and then send back the barrel with the stuck casing (knowing that will happen); or should I just take it as a loss, not spend any more time messing with it and just make sure to only shoot .223 ammo through it? Or, are there other cost effective options? Will a gunsmith ream a nitrided barrel chamber? Thoughts please?

Have you measured your cases that were fired from that rifle? A friend I met at my gun club purchased an ATI AR because it was the cheapest model available. His headspace measured .001" short of accepting a field reject gage.

Leade to rifling I don't know, but headspace is ridiculously long for a new rifle. It's so bad he stuck a case in his resizing die which I helped him remove.

Headspace and throat length are entirely different issues. If your rifle has good headspace it will feed and function fine with .223 commercial ammo and reduced hand loads, even with a short .223 throated chamber.

It may or may not work well and be safe when using NATO spec ammo. No rifle is safe to fire with any ammo if the bolt will close on a field gage. The field gage usually indicates the headspace is .010" longer than SAAMI minimum.

There is no difference in dimensions between so-called 5.56 ammo and 223 ammo. They are identical. The tests you describe don't really mean much.

The Michiguns gauge tests the throat diameter and depth, but what is it that you're trying to determine?

That M4c thread is full of derp and should be disregarded.

Your OP echoes that thread, with the misconception that there are "223 chambers" and "5.56 chambers". There are literally dozens of chamber designs for the 223 Remington/5.56x45 cartridge. One particular chamber design is SAAMI standardized. The only difference between a so-called 5.56 chamber and a SAAMI 223 chamber is in the throat, which is in front of the cartridge case.

For better or worse, there are tons of Wylde chamber barrels on the market and tons of people who want to buy them. The exact chamber specification is not mentioned on the webpage for the barrel you linked to. My suspicion is that you have a Wylde chamber barrel and that the "5.56" ammo you are dropping in is typical 55gr FMJ. Take a look at one of your ejected live rounds and see if there is a burnished ring around the bullet about 1/8" in front of the case mouth. If so, you probably have a Wylde chamber. The Wylde is one of those chamber designs for the 223/5.56 cartridge which is not the SAAMI standardized chamber, but has achieved a level of name recognition so is popular for marketing reasons.

Different bullet shapes from various styles of bullets are more or less likely to make contact in a Wylde chamber. It's the major reason I do not recommend the Wylde chamber for a general use AR type rifle.

With all that said, what is the question or problem that you are trying to troubleshoot?

I have not actually fired any live rounds yet because of the issue I found. Based on my research the 5.56 rounds of ammunition are getting stuck because the bullet is getting jammed into the shorter leade/throat of the .223 chambered barrel. Since I read this is dangerous, I have decided not to fire it yet (or ever) depending on what I continue to find out. Also, when I shine a flashlight down into the chamber and barrel I can see where the copper of the bullet is hitting the barrel. Since it is the bullet that is jamming into the rifling I am that much more hesitant to fire a round and am quite certain that would be very unsafe.

Pictures of chambered and extracted rounds?

I completely agree.

The other thing to consider is that the throat could have a slight edge or burr left by the reamer.  I would go out and shoot a couple mags of 223 through it and see if it cleans up.

Will someone please approve my pictures since I am below 50 post count?

The difference between the 5.56 ammo I have cycled through it and the .223 are the lines you can see on the bullets in the pictures. The .223 ammo only showed marks from going up the feed ramps.

This is why I got concerned about shooting it: http://www.fulton-armory.com/faqs/AR-FAQs/556-vs-223-Chambers.htm

Here's the problem. Many NATO cartridges have bullets that will become jammed into the rifling of a SAAMI chambering (the throat is too short). This is VERY DANGEROUS, for a grat number of                   reasons.

I'm not seeing anything that would make me nervous . . .

What makes me nervous is all of the forums and articles I have read that note that if you feed 5.56mm NATO cartridges into a tightly-throated .223 Remington chamber you can jam the bullet nose into the start of the rifling which can increase chamber pressures and potentially cause damage or even injury as well as cause premature chamber wear. That is exactly what I see happening in my case, the 5.56 ammunition bullets are hitting in a way they hypothetically shouldn't. Now, if the bullet nose jamming into the rifling is really not that big of a deal then I will give it a go, but when I see comments on how dangerous that is I hope it is understandable why I am leery?

First off, someone actually tested the "5.56 in a 223 chamber" and disproved the hysteria:

http://www.luckygunner.com/labs/5-56-vs-223/

Second, some bullet designs touching the throat is a design feature of the Wylde chamber and other chamber designs. It has nothing to do with "5.56 ammo" or "223 ammo", it's the shape of the projectile in combination with the way the throat is cut. The 55gr M193 bullet shape is one that frequently makes contact. M855 types have a different shape and usually do not touch.

With that said, in the photos it appears that the bullet is not scuffed all the way around, but has two specific markings on it. If those rounds were dropped into the chamber and not fed from a magazine, that would make me think there are some serious burrs in that chamber, or that the chamber was incorrectly cut.

Thank you for your replies and information. I have leaned a lot reading up on all of this. The 5.56 rounds that I took pictures of were fed from a magazine where I cycled them by repeatedly pulling the charging handle and dropping the bolt carrier group. In contrast to when I did it previously and had jams with failures to extract with the next round getting caught on the round already in the chamber, the time I did it and then took pictures there were no jams or failures to extract. Guess it is time to go shoot it and see what happens.

Feeding from the magazine, especially on a brand new rifle, will result in scratched up ammo, mostly from the barrel extension.

Your avatar pairs very nicely with the bolded section. Solid post(s) all around.

OP. Do yourself a favor. Listen to people like Gamma. If you buy into the nonsense on some other sites you'll forever second guess every single component on your rifle. Other places exist almost entirely as a marketing tool for a select group of brands and shops. The sooner you learn that, the better off and happier you'll be.

No standard bullet seated to magazine length (2.250" or shorter) will touch the rifling in a Wylde chamber. The now discontinued blunt nosed Speer 70 grain .224" soft point probably would, not any 55/62 or 77 grain and lighter match bullet that I have ever tried.

Ammo that sticks in the chamber and forces the owner to mortar their rifle to eject it out, has a headspace problem. The OP's NATO marked ammo is binding in his chamber. When bullets stick in the rifling that hard they usually stay stuck. When that case is finally ejected the powder flies everywhere and the bullet needs to be pushed out with a cleaning rod. It got jammed in the rifling.

The case shoulders need to be set back more (die turned down more) to make ammo that will fit in this particular rifle. That rifle has headspace close to, or at SAAMI minimum.

Well first, thank you all for sharing your thoughts, I greatly appreciate it. So, just to give an update, I am planning on shooting the rifle this weekend at a range running a couple hundred or so .223 rounds first, and then if that goes well (which I am sure it will since .223 cycles just fine) I am then going to manually cycle some 5.56 to see if it sticks. If it doesn't, I am going to give it a go with 5.56. I will update on Sunday or Monday. Thanks again everyone.

It could be that the 5.56 ammo's case diameter is out of tolerance. Dropping a round in by hand that is too long (cartridge headspace length) will usually not cause it to stick in the chamber unless the bolt is allowed to go forward. Too large of a diameter down at the head will cause it to wedge. Especially so when fed by dropping the bolt. It appears to be factory ammo. Exactly what ammo is it? Do you have access to an RCBS Precision Mic? These are very handy and while designed to check cartridge headspace when reloading they can also be used for troubleshooting ammo and chamber issues.
Also, with respect to the gauge you bought, in what dimension does it show your chamber to be too tight?

Can you pull the charging handle back and leave a round stuck in the chamber? If so, then you also have an extractor issue.

 

The ammo that sticks is Federal 5.56 55GR XM193. I have a friend who reloads so I will ask him about a RCBS Precision Mic. The chamber gauge I used to test was this one: http://www.m-guns.com/tool_new.php?product=gage

When I pull the charging handle on .223 I have no problems cycling the ammo, but when I try the 5.56 it sometimes won't extract. And, obviously I haven't shot it yet. Every time I think I will have a chance my weekends get filled up with chores, yard work, kids soccer games, birthdays, and a bunch of other stuff ha-ha! I am hoping for this weekend though.

We he said. I tried to find a 52 to 75 grain that hit the rifling but I could get no closer that about .070" (Wylde Chamber).