I have read the previous threads on Barrel Life. I realize the condition of a barrel is subjective. But how many rounds of Military 5.56 is a chrome lined barrel with regular required maintance good for? Has anyone worn out a barrel and how many rounds would you estimate you fired before the accuracy degraded?( Groups greater than 2-6inches at 100yds) Maybe the full auto guys would know more however the heat from full auto probably effects their barrels more than semi would.
My question is the army M16s seem to go 20K rounds and others seem to average 5Kto 10K before they replace. Any comments or records

With a chrome lined barrel the amount of full auto fire is the single biggest factor in wearing out the barrel. What happens is the throat area is subjected to the sustained heat and flame of non stop firing. Even chrome plating is affected by this, and once the throat erodes far enough the barrel will no longer hold the required minimum accuracy on the zeroing target. Bump firing and rapid firing don't subject the barrel throat to the same kind of erosion that full auto fire does. The Army dosen't keep track of the individual round count on rack issued weapons, so I can't give you anything but a guess on how many rounds it takes to affect accuracy. Blanks don't help things either, and the military uses themin abundance. Target rifles generally go a minimum of 5k rounds before accuracy suffers, and chrome lining is usually good for double that number so I'd guess 10k is a minimum number.

From Bushmaster.com -

Gov't. M16's can show throat erosion after as little as 2,500 rounds. However, that is with the lighter Gov't. profile barrel and always under full auto conditions. Under semi-auto conditions, those barrels will typically go 5 to 7 thousand rounds before breaking down badly enough to warrant replacement. Many times, a Gov't. barrel with 1 or 2 thousand rounds will be replaced as inaccurate, when what it really needs is to have the copper fouling removed from the bore. This is a tedious job, but the reward is a "like-new" barrel. This refers only to chrome lined barrels like ours or Colt's. Mil spec. SS109 ammo will not measurably increase barrel wear under semi-auto fire and our mil. spec. (chrome lined) barrel will outlast any sporting rifle barrel - period. More barrels are ruined from over cleaning - or careless cleaning - than are ever "shot out". Chrome lined barrels really only need to be detail cleaned when the groups start to suffer. Otherwise, a little powder solvent (or "Break Free" with CLP), and a few passes with a brush, clean the chamber well, dry everything off and apply a very light coat of "Break Free" or "Rem-Oil" and put it away. We have had barrels here go 20,000 rounds and still be within mil. spec. when treated this way.

Thanks for your info. and fast reply