Just got another M4, this one is brand new unfired. It is amazing how the detent in the bolt, is a lot looser than my older M4 that is probably well over 15 years old. my older one is an aluminum trigger group, new one is polymer. The new OEM bolt handle is sloppy, due to the lack of spring force in the detent, old M4 the OEM handle is very solid in place with more force from the spring.
Is this normal for newer M4s? Just thought it was an interesting development. I wanted an older one and newer one for R&D. I will take a look at it in more detail later, I'll try and loosen up the detent with some oil and see if that helps. An interesting observation regarding perhaps the lack of quality control present in new production models.