FSB question

[cohiba]

I thought I knew the answer but then someone throws in an opinion and now I'm doubting myself.

I'm building a SDM-R upper with a flattop upper sporting a Matech BUIS. I want to use a standard FSB. Because I'm using a flattop, I figure I need a "F" marked one, which I have.

Someone else mentioned that an "F" marked FSB is for 14.5" and 16" uppers only, which makes zero sense to me. It's a flattop, what should the barrel length matter? Of course, I've been wrong before...once...in 1985...and I still haven't gotten over it... so any help would be appreciated. Thanks.:D

[markm]

Someone else mentioned that an "F" marked FSB is for 14.5" and 16" uppers only, which makes zero sense to me.

All I know is that I had a COLT factory assembled flat top 20 inch upper. And it CAME WITH THE F Front sight base, Mama.

[Robb Jensen]

I thought I knew the answer but then someone throws in an opinion and now I'm doubting myself.

I'm building a SDM-R upper with a flattop upper sporting a Matech BUIS. I want to use a standard FSB. Because I'm using a flattop, I figure I need a "F" marked one, which I have.

Someone else mentioned that an "F" marked FSB is for 14.5" and 16" uppers only, which makes zero sense to me. It's a flattop, what should the barrel length matter? Of course, I've been wrong before...once...in 1985...and I still haven't gotten over it... so any help would be appreciated. Thanks.:D

As you thought F height FSBs are for flat top use for all barrel lengths.

[cohiba]

Thanks guys. 1985 lives on alone. ;) :D