Ok, I have narrowed down the barrel configuration that I want to slap on my BCM lower I just received today, however I am undecided on which rail configuration to choose. I am in between these two:
it depends on which front sight config you want and how much rail. some really like the standard FSB. personally i would go with the 12" rail because the added space, not so much for cramming accessories on it, but so you would be able to get your hand way out there for stabilization. and of course throw a Troy folding front on it.
do you have long arms? Depending on the way you hold the rifle, people like to hold their support arm as far forward as you can. It aids in controllability. If you plan to use an optic and/or want flip sights, I would go with the 12" rail.
I have the 12" rail on my middy and have a magpul AFG mounted up front
I am 6’1" and have fairly long arms. I have an RVG on my issued M4 and find it pretty comfortable even on the 7" rail using the thumb brake method so I’m thinking the 9" rail might suit me well. As far as optics and lights, I have an H1 and a scoutlight to put on.
For anybody over 6 foot I’ve seen them favor 10-12" rails depending on accessories and if they adopt a more squared up modern carbine stance. Guys that feel more comfortable shooting bladed don’t mind the 9" rails. I’m a five foot nothing pip-squeak and prefer 11-12" rails for the extra sight radius and room when I extend my reaction arm to stabilize the barrel.
OP make sure you find markm’s post on that upper you linked, he has good footage and photos of it in action. It is a honey of an upper and I usually favor 16" barreled guns now.
I have been following that thread and the upper seems outstanding. A part of the reason I am going 14.5 middie. I’m just not sure what rail would suit me better. Maybe I need to get hands on with both.
Thanks for everyone’s thoughts and opinions, please keep them coming.