Dust cover up or down?

[berettaprofessor]

Just realized, after buying a 224 Valk upper, that some AR dust covers open up and others down. Today’s new toy opened down, which freaked me out until I looked at others and found some opening down or up, even within the same caliber, without obvious reason.

So, why? Just due to manufacturers whim? Is there a real advantage to one or the other?

 

[berettaprofessor]

Uh...duh. I may have just answered my own question. Is it simply that all right ejection ARs open down and all lefty ARs open up? I have both and didn’t notice which did which as to their handnessness.

 

[someguy2800]

I’ve never seen one that opens up

 

[WestKentucky]

I assumed that lefty guns opened down too. I have never seen on that hinges up.

 

[ColoradoMinuteMan]

Left-hand ejectors open upwardly to avoid the ejection port door hitting the bolt release.

 

[9mmepiphany]

So, why? Just due to manufacturers whim? Is there a real advantage to one or the other?

The original production dustcovers were designed to flip open under spring tension as the bolt moved to the rear. It made sense that they spring downward in case the spring failed the ejection port would still be opened as the dustcover would hang down under it's own weight and not interfere with the ejection of cases. It was also easier to close the dust cover by bringing the trigger finger up under it.

An upward swinging dustcover would cover the ejection port if it's spring failed. To close the cover, you'd have to reach over it to bring it down