i sometimes see a comment over at the mall-ninja AR15/M4 boards that goes like this.
X-brand of gold plated mall-ninja weapon brand new out of the box is short stroking,FTF, double feed ect ect-- and the guy that owns this device is well pissed because he spent $$$$ of dough and the damn thing and it won't run, or won't run with steel cased ammo and so on.
outside of the usual user error i sometimes see the comment "well fire a few hunderd/500 /1,000 rounds and after it is broken in the problem should go away!"
now granted on some of my AK builds they did need a few rounds to loosen up and start running on some of the builds. but most of the time they didn't. and by few rounds i mean one mag or less.
i can't say i am some kind of AR-15 guru but over the few years i have assembled a number of these weapons and nearly every damned one of them ran right out the door. with the exception of one LMT upper which had a metal fragment lodged in the gas vent on the barrel and no amount of ammo would have dislodged the metal shrad lodged in the port. after a few rounds i knew there was something wrong with the upper and by a quick process of elimination i ended up removing the gas tube/FS base and then peering down the gas port on the barrel.
the question of the day is this? you folks ever see a new AR type that needed a "breaking period of 100 or more rounds" where there was nothing reallywrong with the weapon??