Do what you want but three of the country's best AR 15 armorers all are on the same page,Ned Christiansen , Dean Caputo and Frank Moody all have dealt with this issue in th same manor. Also XM is not reject ammo according to Federal :
All our Xm193 ammunition is manufactured by LCAAP and is first
production run, the XM193 is a 5.56 cartridge and is not interchangeable
with the 223. The Xm855 is also first production run made by LCAAP in
5.56 and is load with a steel penetrating bullet.
Thank you
From Ned Christiansen:
Neck and Throat 5.56 Reamer
A common problem when firing 5.56 mil-spec ammo in an AR15 with a SAAMI-spec .223 chamber, is that once in a while a spent primer will fall out of a case as it is extracted. Sometimes the primers fall clear and there's no problem, other times they will go under the trigger and get wedged, rendereing the rifle inoperable. I've seen some extreme cases of this where the hammer and trigger were actually hard to get out. I've seen them get wedged between the charging handle and the inside of the receiver, with the bolt out of battery, so that the gun had to have the stock removed so the bolt could be removed to clear the primer. It is not unknown for the primer anvil get stuck on the tubular portion of the carrier key! Popped primers are due in part to the tighter, shorter freebore and shorter, more abrupt throat of the .223 chamber, causing a pressure spike with the hotter, mil- spec ammo. This reamer will address these areas as well as making sure the neck diameter is not too tight or short, without changing headspace. It does not cut the shoulder or anything behind it; it stops off on the shoulder. Of course, whatever rifle you're shooting, you could just look at what's stamped on the barrel-- it might say .223, or it might say 5.56, or it might say nothing. You could call the manufacturer and ask them what chamber you have, but even if you get to talk to somebody who understands the question, they likely don't really know. They may tell you what you want to hear, but truth is, not many AR15 manufacturers make their own barrels. They buy them from someone else, so they don't really, truly know what chamber you have. Some of them will flat decline to discuss it with you.
This reamer is designed as an easy, quick and sure way to know. You just open the upper receiver, remove the bolt group, drop in the reamer with some oil, and slowly turn it in (clockwise only, never reversing it), using a lot of turns and very little pressure. The handle centers itself in the upper receiver. When ithe reamer bottoms out on the chamber's shoulder it will spin freely-- it has stopped cutting and you are done. When you have done this, you know for sure you have a chamber with proper 5.56-plus dimensions in the critical freebore and throat area. Primer popping due to pressure spikes in a short leade will cease, but be advised there can be other factors in popped primers such as hot ammo, hot chambers, and improperly loaded ammo. The new version ($240, shown above) has a redesigned handle that is custom machined from aluminum barstock, so it is quite a bit lighter (handle and reamer weigh less than the original handle alone). It is also shorter to take up less room in your toolbox, and, most importantly, it functions as a storage case for your reamer. When you are finished reaming, simply remove the reamer, reverse it, and insert it into the handle-- your expensive tool is now very well protected and not taking up extra room in your toolbox. There is also a slot in the handle to accept the Allen wrench you need to turn the set screw that retains the reamer. The Allen wrench is retained in the handle so everything you need is right there.
What about chromed-lined chambers? The good news is that in my experience, Colt AR15 chromed barrels have a proper 5.56 chamber. I would consider most others to be suspect. The reamer has been subjected to a secondary heat-treating process, titanium carbo-nitride, which makes it capable of correcting under-spec chromed chambers. Obviously it will do fewer of them, but I have yet to hear of one of my reamers geting dull-- and my personal one has done at least a few dozen chromed chambers. Will removing the chrome be a problem? No. Plenty of AR's don't have chromed bores and chamber and they work fine. I've sectioned some chromed barrels and the chrome doesn't last that long in the throat area anyway. Removing chrome in the chamber won't cause the area to peel like bumper chrome.
Reamer with new lightweight/compact handle that doubles as reamer storage: $240
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