Hey my AR-15 friends! I am getting ready to purchase the BAR rail for my DPMS AR-15. Right know I have a Carbine length by Magpul. I am stuck between which BAR rail to get. Anyone have any ideas of what I should go with? I know its my choice. I figured someone that might have the 9, 10, or 12 BAR already might have some good input. One last question with the BAR rail having a bigger diameter, will it fit over my factory picatinny gas block?

I doubt the BAR will fit over your railed factory gas block. You would need to get a low profile gas block to utilize a rail longer than 7 " (due to your barrel being a carbine length gas system).

Along the lines of length, it depends on where you like to have your support hand and how long your arms are. If you like to run your hand closer to the mag well, then a 7" or 9" would probably be better for you. If you like to extend your arm out as far or almost as far as it can go, then a 12" could be better. Go to some shops and pick up rifles with 9" and 12" rails to see which feels best for you.

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Forget the zombies... I'm getting ready for the Terminators...

Well, I can't say anything about the BAR but I have a 12" SAR and it feels amazing in my hand.

I extend my arm kinda far out. I'm pretty tall and skinny, 6'0-6'1 and like 150 lbs. So kinda a lanky build and long arms. Here's a pic of it with an afg 2 now. I will probably keep the afg on it but not sure. I might also extend it out a little further. But this is just to show you an idea of what it looks like, how far out I hold it with my build, and I'm pretty sure the BAR and SAR have the same height and just different width.