Originally Posted by rockquarry

Use a case gauge if you'll be loading for any AR. It will eliminate jams and malfunctions due to out-of-spec case and cartridge dimensions. I found out quickly that cartridges with partially neck-sized brass I used in a .223 bolt-action would not work properly in an AR. Even what appears to be full-length sized brass may require the size die to be screwed in a little more to work in an AR.

As for case trimming, it will be required periodically. A too-long case may function in an action, but it's not a safe practice. It takes only a split second to check case length after sizing brass.