I recently had a hankering to build an XM4/727 inspired carbine. I'm not a cloner and just wanted the general aesthetics. I've always heard that I need a standard height non-F A2 FSB with an A2 upper. I've read a bunch of threads online and opinions seemed pretty divided on the necessity of it. After waiting a couple months for a WW M4 profile barrel with a standard height FSB, I got impatient and pulled the trigger on an A2 upper with a 14.5" p/w Colt SOCOM barrel and an F height FSB.

Finally got a chance to zero it today. I did a standard 25/300 Army zero, mainly because I had a pile of Army zero targets. All I literally had to do was crank the FSP down 5 clicks and it was dead-on. Zeroed in 9 rounds. Still a decent sight picture and not the "little nub" that I have heard folks refer to with this combo. Just wanted to share if any other non-purist carry handle aficionados are considering an F height FSB carbine barrel and an A2 upper.

I’m using a Ffsb on a Colt 10.3” barrel & Colt C7 upper… no issue zeroing it


Nice built btw!
I still have an A2 receiver laying around…

Nm.

Interesting. Never heard of this (XM4) before and here's the 2nd reference I've seen in as many days.

Nice.

It's a neat little carbine. I say XM4ish because a true XM4 would have a unique barrel profile. This is just an A2 carbine with an M4 profile barrel, fat double heat shield handguard, and CAR stock. But it looks "gud enuff" for a non-cloner like myself. Lots of good info in the pinned XM4 thread in this forum.

https://www.ar15.com/forums/AR-15/XM4-Clone-Information-thread/127-740736/

I have a Del-ton A2 upper with a DSA 14.5 carbine barrel with an "F" marked FSB installed.  It zero'ed at 50/225 fine and sight picture is acceptable.  My results were similar to yours, and as you said, an M16A2/XM4 carbine is mighty handy.

lol, even a pinned thread. No idea how I missed this.