I think everyone is putting M4 feed ramps on their barrel extensions now. I don't know if it matters.
Go with carbine length gas with a carbine buffer. Pistol length is ridiculously short. I have a Wilson combat barrel with carbine gas and it works fine with lighter 125 grain bullets but short strokes with subsonic. If you have "short stroke" problems you can always drill out your gas port or fool with different buffers. I've read that subsonics work better with a suppresser.

I hope that answers some of your questions. 300blktalk.com is a great source of information.

Saw this today and remembered your post. If you haven't already got your barrel yet this one has free shipping.
http://arbarrelkings.com/collections/300-aac-blackout/products/copy-of-300-aac-blackout-16-barrel-1-8-twist-5-8x24-tpi

WJ

Saw this today and remembered your post. If you haven't already got your barrel yet this one has free shipping.
http://arbarrelkings.com/collections/300-aac-blackout/products/copy-of-300-aac-blackout-16-barrel-1-8-twist-5-8x24-tpi

WJ

You are really pushing that website.

https://www.full30.com/video/f868df001ebce3caa6c2c54102472524

Interesting 300blk discussion

You are really pushing that website.

I've purchased items from them and they seam stand up, good people. In today's world that's not easy to say about a internet company. For me if some place works well I don't mind telling people about it but also If it don't work I WILL tell anyone about it.

I would order from OKWeber. They are a reputable shop that have been around for years. I think they are a small operation. Sometimes small shops take a few days to ship.

I ordered 500 ct. Sierra 125 gr. MK on Wednesday afternoon and arrived today.  They mailed it Thursday morning USPS 3 day priority.  The site shows a shipping menu as you are checking out.  They are GTG from this experience.