AR-15 barrel length help?

I just bought an AR-15 lower receiver, and I'm planning on building a complete rifle from a kit. I'm concerned over what barrel length and options to order. Most of my shooting will be under 400 yards, and I'd like it to be somewhat portable. What barrel length, optics, etc, would be ideal for what... show more I just bought an AR-15 lower receiver, and I'm planning on building a complete rifle from a kit. I'm concerned over what barrel length and options to order. Most of my shooting will be under 400 yards, and I'd like it to be somewhat portable. What barrel length, optics, etc, would be ideal for what I'm doing?
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