Big Bore Uppers
Thought I would post this tidbit of info for those who have had ejection and or feeding problems with their ARs and AR builds notably 458 SOCOM, 450 Bushmaster, 50 Beo etc.
Make sure you are using a big bore upper receiver. Have seen this problem countless times at the range. In some cases even with newly purchased complete uppers. Big bore uppers are not milspec, they are machined with a larger opening.