I have another small batch of these ready:
(from my site, http://m-guns.com/tools.php)
"Neck and Throat 5.56 Reamer - (bottom two items in the top image) 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. We’ve seen some extreme cases of this where the hammer and trigger were actually hard to get out. We’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. We have seen the primer anvil get stuck on the tubular portion of the carrier key! Popped primers are due in part to the tighter freebore and shorter, more abrupt leade or 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. It is provided with an extension T-handle that has a Nylon bushing on it, so you can just open the upper receiver, remove the bolt group, drop it in with some oil, and slowly turn it in (clockwise only, never reversing it), using a lot of turns and very little pressure. The Nylon bushing centers the extension in the upper receiver. When it bottoms out on the shoulder it will spin freely-- it has stopped cutting and you are done. When you have done this, you know for sure you have chamber with proper 5.56 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.
What about chromed chambers? The good news is that in our experience, Colt AR15 chrome-lined barrels have a proper 5.56 chamber. I would consider any 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, and I can’t say what the numbers would be as I have not had to ream that many chromed ones yet. 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 long in the throat area anyway. Removing chrome in the chamber won’t cause the area to peel like bumper chrome. The reamer, complete with T- handle, is $210."
Please add $10 for shipping (Priority Mail)