Frustrated!! - My S&W M&P AR Won't Cycle Reloads

[Old_School]

Most likely, cases have been in adequately sized. As a previous poster mentioned, you may need a small-base sizing die for that rifle's chamber.

 

[1006]

If the bullet has a rounder looking profile, there is good chance that they are simply loaded a little too long. If that is not it, double check the cases for proper sizing.

Crimping is optional, but should never adversely effect the function of the gun.

 

[Fieldnstreamer]

Try small base dies?