There are a lot of match rifle shooters who baby their barrels and shoot tailored loads that pull the barrels off their Sprinfield M1A's at 5,000 rounds. While this is a different situation, those shooters feel that the barrel has served it's useful precision shooting life by 5,000 rounds. If I'm not mistaken, the 'reject' standard for new military M16 rifles in the US is somewhere around 5 inches at 100 yards gross accuracy (they look at the group differently and have standards for dispersion by hit location on target, but functionally, assuming it's centred the group should be around 5 inches).
As far as "rethinking" purchasing a $700 gun because it loses accuracy after shooting just $4800 dollars worth of ammunition, that just seems odd to me. 12,000 rounds is a lot more ammunition than the average Norc shooter will put through his rifle in 2 lifetimes. The OP isn't the average Norc shooter (the presence of an LMT in the household pretty much proves this) he's a fairly serious shooter who has a lot of time behind the gun. On a side note, OP -apart from the current accuracy thing, what is your opinion of the Norc, I haven't heard of too many people with that kind of mileage on one.
Thank you for the specifics and the perspective wrt to competition shooters. It helps to establish parameters to start cross comparing relative accuracy degradation as the barrel wears.
Going through the MIL standard for the M16A2 (MIL-R-63997B) and for the M4A1 (MIL-C-71186), I was able to find, interestingly, an acceptance criteria for targeting and accuracy of the barrels - Figure 1, Section 3.4.6, Amendment 4. If I am reading the charts correctly, it states that the extreme spread for a 10 shot group must not exceed a 2"x2" square at 100 yards. Note that this is shot using iron sights and there is no mention of using a mechanical rest.
So this means that, in absolute terms, my Norky, when new, would have probably flunked this acceptance test and the LMT would have had a slighty higher chance of passing it. After ~12k rounds, the Norky flamboyantly fails
Note that this acceptance criteria is for new manufacture rifles, I was unable to find any supplemental information for acceptable accuracy of in-service rifles. I'll keep looking, but would appreciate any leads to documentation
The rifle itself has held up remarkably well. In fact, it has far exceeded my expectations. I have not replaced any part (although I inspect them regularly) and neither has anything broken. The finish has held up very well with no uneven wear marks or chipping. The only cosmetic flaw has been that the stock buttstock has gotten a little wobbly with use and I'll be replacing it one of the Magpul ones soon. Mechanically, it is in good operating order and the trigger is smooth.
Initially I had a few FTF and FTEs but once it broke-in after a few hundred rounds it's been running like a champ. Now it only jams up very very infrequently, and usually only when I run MFS ammo. They just don't seem to like each other
My biggest complaint has nothing to do with the rifle, but the supplied magazines. They are junk and contribute to most of the failures. I use Magpul PMags exclusively, but even their spines crack under heavy use so every couple of months, I have to get new mags
In short: it is a tremendous buy for the price and other than a few cosmetic finish issues, is at par with most North American manufacturer's offerings. I have no regrets buying one and will continue to use this rifle (abeit with a new mid length barrel) alongside my (much) more expensive firearms.