Here's my experience with my NEA 18 DMR -rifle.
First off, the chamber was unfinished, it left a nasty "belt" in the fired brass.
After a gunsmith cleaned the chamber up, there weren't any issues for about a year.
Then the bolt broke in in half. At that point, round count was about 3400.
The broken bolt got replaced with a chromed bolt from NEA.
After just 340 rounds, trouble started again. The locking lugs of the new bolt had considerable deformation.
Also, pieces from the lugs were chipped off.
And once again, the gun was sent to a gunsmith to be inspected.
The gunsmith inspected the rifle and these are his findings:
Headspace is 0.12 millimetres(or 0.0047 inches) over the C.I.P.(equivalent of SAAMI) maximum (Headspace was OK when the replacement bolt was installed).
Barrel extension is most likely damaged too as headspace was over the maximum with numerous different bolts.
The BHO groove in the lower receiver has been deformed, bolt doesn't lock back with empty magazines.
The upper receiver is also really worn out; for example, charging handle is reaaally loose in the upper.
Total round count with the rifle is little over 3700