This may be a dumb questions, but what is an “F” marked sight tower? What does the “F” mean? Where would the “F” be on the sight itself? What is it if there is NO “F”?
Flat top.
It is properly installed on ARs that use the M1913 rail on the upper receiver. there is a little tiny F on the FSB if you look.
All I see is an “R1” inside of a circle on the right hand side.
Did the barrel come with an A1 or A2 upper? Those don’t use F marked.
As far as I know, the upper was a complete unit with a 16" profile barrel and “T” marked upper receiver. I was told it was off of a Colt lower that couldn’t be imported into California.
Just a little clarification, Cali, to help you on your journey.
A2 upper:
A1 upper:
A3 and A4 are flat tops.
F marked
The barrel length is 16" or 20" etc.
Barrel profile is the shape in terms of thickness
Government profile:
Heavy barrel
M4 profile
Okay, it is an M4 profile barrel. And it’s on a flattop receiver…so will I have trouble mounting and zero’ing say an Magpul MBUS rear sight? What are the repercussions of using a NON “F” marked sight tower with a flattop and an MBUS?
you have to buy a longer front sight aperture.
I think bushmaster sells one.
That kinda sucks…maybe I’m in a little over my head? Would it be better/cheaper/easier to buy an “F” marked sight tower or even railed gas block and throw a complete set of MBUS’s on it?
The Bushmaster extended front sight post is simple to screw in and only costs a few dollars. Much easier than changing the FSB. It takes just a few minutes to remove the old post and install the new one.
Ah, I misunderstood…
My BM came with an A3 receiver and did not have the F marked FSB. After removing the carry handle and installing my ARMS #40, it consistantly shot high even after I backed the front sight out almost all the way.
I called them out on it with a phone call to their service department. After talking to their head gunsmith for about 1 minute, he told me that he would arrange to send me one of their taller front sight posts free. I had it in my hands in 3 days and swapped it out.
what kind of upper do you have?
I’m not sure about the upper…I was told it was off of a Colt, but the only possible forge mark I can find is a singular dot just forward and below the forward assist…here are some pictures of my FSB…the second shows the ONLY marks I can find on it…
Can anybody identify these marks?
i’m thinking that’s not a colt upper… i’m reasonably certain that all colt railed uppers have F marked FSBs. does the barrel have a “C MP” stamp?
one other thing i might as well mention- that sling attachment will melt pretty easily
The barrel has no marking unless they’re under the barrel nut. As for the sling attachment, would it effect accuracy if I tethered the sling to the FSB itself?
not really… it IS tied to the FSB itself. what are you saying?
doesn’t sound like a colt upper. scotty will be able to tell you for sure, i’m sure. PM him if he doesn’t happen upon this thread.
It’s more like tied around the barrel/gas tube…Who is “scotty”?
this is an FSB… just so we’re clear
the barrel, FSB, and gas tube all get hot enough to melt nylon in a flash
scotty is “scottryan,” and he’s our resident colt-savant.