Hello men, I need some brain power of this.
I found some heavy .223 (80gr) loads on ammoman.com that mentioned use only in a throated match rifles. I have a Colt Match Target Lightweight, 16" 1:7 with barrel markings that read "C MP 5.56 NATO 1/7".
When I read through the AR15.com AmmoFAQ, it shows and discusses the difference between .223 and 5.56 chambers. The mil-spec 5.56 has a throated chamber compared to the SAAMI 223.
So now this makes me ask some questions...
Is my AR throated?
How can I know?
If I can shoot 75 grain all day long, what would make the 80 any different? I though I could shoot any 5.56 cal loads.

I am asking all you big brained AR-philes to please help me in getting fully knowledged in this subject.

Many thanks in advance!
Ed in Illinois

ALL rifle barrels are throated. The throat is the area just forward of the chamber where the neck ends and where the rifling begins.

What is unique about the 80's are that they are designed for single round feeding. They will NOT go into a magazine. The problem is that with all of the different AR chambers out there, the throat varies quite a bit between chamber designs and even between rifles. As the life of the rifle goes, the throat lengthens as the rifle is shot. This is called throat erosion. The throat lengthens over time. What you do NOT want is to fire a long seated bullet into a short throated rifle. Besides the chance of seizing up you can also expect higher chamber pressures as well. Most mil spec chambers are NATO chambers and they have the longest throat of all the chambers such as the Wylde, CLE, PPG, and commercial .223 Remington chambers. To touch the rifling with the Sierra 80 grain bullet in a NATO chambered rifle the OAL needs to be +/- 2.550". This can and does vary a bit due to wear on the barrel and the OAL of the bullet itself. Depending on the OAL of the loads you want to buy you should be safe, what will probably have happen is that they may be seated shorter to allow for another shorter chamber other than the NATO chamber you have. What is the OAL of the loaded rounds ammoman has? But remember, these loads fire one at a time and need to be single loaded by hand.

I beg to differ on that. The military chamber is the NATO chamber and it is by far longer in the throat area than any of the match aftermarket chambers on the market. As I stated before, to seat an 80 grain Sierra to touch the lands in a NATO chamber the OAL will be right at 2.550". And at that there is not a whole lot of bullet remaining in the case. With the Wylde it is right at 2.465" OAL. With the CLE and Bushmaster DCM chamber it is right at 2.435" OAL. It will vary a bit as to bullet OAL etc. I have yet to see or find a chamber reamer that will have a longer throat then the NATO chamber.

Also, most shoot the 80's at 600 yards and some even shorter if there is a slow fire stage. 1000 yards is okay for the 80's but most do not load for supersonic flight. The JLK 90's are more for 1000 anyway, and of course this takes a tighter twist than most use, a 1 in 6.5" for a 20" barrel.

The reason for the warning is to avoid someone trying to chamber and fire them in a shorter chamber than what the bullets are seated to. Of course you could then just measure your chamber and re-seat the bullets to make sure you have enough jump.

OK, I'm catching on here.
I will stick with whatever-can-fit-in-my-magazine type ammunition. Then I know I'm safe.

Thanks for all your help guys!