Where can I find NON-F marked barreled assemblies?

[OmOpLaTa]

I'm posting this question in 'gunsmithing' vs 'rifle' section because I thought this may be the better place to post it.

Anyways, where can I find NON-F marked barreled assemblies? I have some A1 and A2 upper receivers and I'd like to start building them. B-kings and TNTE won't ship to CA and Brownells does not have any in stock, except a 12.5" 1/12 twist. I'm looking mostly for a 16" or 20" barrel, but open to other lengths.

 

[AR15barrels]

F has nothing to do with flattop receivers.

F height is for carbines.
The F denotes the sight as being taller, which is required to make the shorter carbine gassed M4 carbines trajectory correct with the 300-600 elevation rear sight that carbines get built with.
Carbine sights were made F HEIGHT 25+ years before they were actually F MARKED.

Rifles all use a 300-800 rear sight and have longer gas systems so the sight radius is longer and they use a standard rifle height front sight base as used on the M16/M16A1/M16A2.
All rifles use a rifle-height FSB and never have an F mark, even if the barrel is installed on an M16A3 or M16A4 which have flattop receivers.
All 20" barrels with a rifle located FSB should NOT be F MARKED or F HEIGHT.

Rather than worrying about if your FSB is stamped or not, worry more about how tall it is:

 

[OmOpLaTa]

F height is for carbines.
The F denotes the sight as being taller, which is required to make the shorter carbine gassed M4 carbines trajectory correct with the 300-600 elevation rear sight that carbines get built with.
Carbine sights were made F HEIGHT 25+ years before they were actually F MARKED.

Rifles all use a 300-800 rear sight...

Very interesting. So basically I can use any F marked FSB on any 16" barrel mated to any A1 or A2 upper?

I recently got an A2 upper receiver without M4 feed ramps, and the elevation knob says '800/400'. Were all the A2's like this?

 

[AR15barrels]

Very interesting. So basically I can use any F marked FSB on any 16" barrel mated to any A1 or A2 upper?

I recently got an A2 upper receiver without M4 feed ramps, and the elevation knob says '800/400'. Were all the A2's like this?

Any 14.5" or 16" 5.56 barrel with a carbine length gas system should use an F height front sight base in order to work correctly with a carbine 300-600 rear sight.
20" 5.56 barrels will have a rifle length gas system and will use standard height front sights regardless of the receiver they are installed on.
If you build a carbine with an M16A2 receiver with 3 to 8 rear sight, your rear sight elevation markings will not be accurate.

M16A2's do not have M4 feedramps.

M16 A2 rear sights should have numbers from 3 to 8 and should be zeroed 2 clicks up from the bottom at 50m for a 50/200 battlesight zero using the 0-2 marked aperature.

M4 carbine removable carry handles have a rear sight drum with markings from 3-6.

 

[OmOpLaTa]

Any 14.5" or 16" 5.56 barrel with a carbine length gas system should use an F height front sight base in order to work correctly with a carbine 300-600 rear sight.
20" 5.56 barrels will have a rifle length gas system and will use standard height front sights regardless of the receiver they are installed on.
If you build a carbine with an M16A2 receiver with 3 to 8 rear sight, your rear sight elevation markings will not be accurate.

What If I were to build a dissipator (16" barrel, rifle length sights (rear sight A2 upper receiver as mentioned above), with rifle length gas system), would the F-marked FSB matter?

 

[AR15barrels]

What If I were to build a dissipator (16" barrel, rifle length sights (rear sight A2 upper receiver as mentioned above), with rifle length gas system), would the F-marked FSB matter?

That won't work correctly with either carbine or rifle rear sight so it does not matter.
Probably better to go F height.
You can always sink the front sight post further down into the sight base but the ears won't protect the post if you raise the sight post up above them.