I have two rifles with F marked FSB's. A friend just bought a Bushy that does not have an F front sight and after zeroing found that the post would not go high enouph for proper zero, obviously needs a higher post. Now three other friends all have FSB that are not marked F and have plenty of adjustment with a regular hieght post, all are flat tops. My question is, are all F hieght FSB's marked with an F or are only some marked as such. The thing that realy through me is one of the rifles is a Colt and the FSB is not marked with the F and has a regular hieght post and zeroes fine with plenty of adjustment left. Not sure of the other manufacturers but 2 of the other rifles were assembled by ADCO. So what is the deal, who marks FSB's with the F?

F marked FSB = "forged"

Has nothing whatsoever to do with the height of the front sight.

There are 2 type of FSBs, "forged" and "cast".

Mike

OK well I guess that is where I was wrong then, I thought that F meant it was right hieght for flat top reciever.

Quoted: I have two rifles with F marked FSB's. A friend just bought a Bushy that does not have an F front sight and after zeroing found that the post would not go high enouph for proper zero, obviously needs a higher post. Now three other friends all have FSB that are not marked F and have plenty of adjustment with a regular hieght post, all are flat tops. My question is, are all F hieght FSB's marked with an F or are only some marked as such. The thing that realy through me is one of the rifles is a Colt and the FSB is not marked with the F and has a regular hieght post and zeroes fine with plenty of adjustment left. Not sure of the other manufacturers but 2 of the other rifles were assembled by ADCO. So what is the deal, who marks FSB's with the F?

"F" FSBs are taller (CMMG uses these) to allow the use of regular front posts with mil-spec DCHs.
I suspect Bushmaster uses a mil-spec DCH (which sits higher) which requires a taller front post or a "F" FSB since Bushmasters can easily turn to "600" yd elevation on the rear sight.

A RRA or DPMS DCH only goes to "5" with the IBZ, and is a commercial-spec DCH, which works with any FSB combination.

"F" does not stand for forged AFAIK.

When I used a Leapers DCH (copy of Colt DCH), it was the "mil-spec" height which required the 0.040" taller front post on my Bushmaster barrel/FSB in order to zero properly. With a standard post, it was practically coming out of the FSB and I was still shooting high.

With my DPMS DCH's and standard front post/FSBs, I have no problems boresighting at 50 yd and the front posts still have plenty of adjustment remaining.

I don't know of many reputable vendors making cast FSBs. My Bushmaster is advertised as a FORGED FSB and it does not have a "F" marking. CMMG has forged FSBs with the "F" marking which signifies it can be used with Colt/mil-spec DCHs w/o using a taller front post.

Quoted: "F" does not stand for forged AFAIK.

And just what do you think it stands for?

Mike

ETA - FYI, not all "forged" steel FSBs actually have a "F" stamped on them and while I'm uncertain of current DPMS made FSBs the older ones were "cast" (as there was more than a few "forged" vs "casted" FSB wars years ago)

So would it only be an issue if one used a DCH? All the other rifles are using Flip up BUIS. Are all colt flat top hieght FSB's marked with an F?

Quoted: F marked FSB = "forged"  -1 Has nothing whatsoever to do with the height of the front sight. -1 There are 2 type of FSBs, "forged" and "cast".  This could be argued, but is mostly correct. Mike

33% correct is not good.  You may want to try posting less and reading more.

Quoted: 33% correct is not good.  You may want to try posting less and reading more.

I was reading everything 4 years before ya even got here.

Mike

Quoted: So what is the deal, who marks FSB's with the F?

Colt Flat top upper halves come with them.  

I've never heard of CAST front sight bases.  I suppose Olympic Arms would use this method.

Quoted: Quoted: 33% correct is not good.  You may want to try posting less and reading more. I was reading everything 4 years before ya even got here. Mike

Good for you Mike.

I'll go with my info, you go with yours.    

Quoted: I'll go with my info, you go with yours.

So what do YOU think the "F" stands for?

Mike

Quoted: Quoted: So what is the deal, who marks FSB's with the F? Colt Flat top upper halves come with them.   I've never heard of CAST front sight bases.  I suppose Olympic Arms would use this method.

So are Colt FSB's that come with flat top assy's marked F or is it just a known thing that if it is a Colt then it is the right hieght?

Quoted: Quoted: I'll go with my info, you go with yours. So what do YOU think the "F" stands for? Mike

I do not know, but Colt might use it to signify that its for a Flatop upper receiver, which would be used with their Colt mil-spec DCH that has the rear sight sitting at a higher elevation from the get-go.

Quoted: Quoted: I'll go with my info, you go with yours. So what do YOU think the "F" stands for? Mike

FSB's from a known quality manufacturer (COLT, BCM) that are STAMPED with the "F" have the sight plane channel milled higher.  They use the same FSB forging.  This has been gone over many times.  You must have missed it.  

take care

FSB's from a known quality manufacturer (COLT) that are STAMPED with the "F" have the sight plane channel milled higher.

f for flattop use no f for use with a2 sight assy.

F is not equal to forged, even though they are forged.

Quoted: FSB's from a known quality manufacturer (COLT) that are STAMPED with the "F" have the sight plane channel milled higher. home.comcast.net/~gocartmozart/front_sight_base2.jpg

MY Colt 20" A4 upper and A2 20" FN uppers have the "F" marked FSB HEIGHT but arnet marked as such...My Bushy A4 14.5" upper has an A2 FSB - but I plan on putting a Slabside upper on it so I dont have to put a higher FSP

Quoted: Quoted: Quoted: So what is the deal, who marks FSB's with the F? Colt Flat top upper halves come with them.   I've never heard of CAST front sight bases.  I suppose Olympic Arms would use this method. So are Colt FSB's that come with flat top assy's marked F or is it just a known thing that if it is a Colt then it is the right hieght?

I'm not sure I understand your question.  I won't say that ALL flat top FSB from Colt have the "F", but everyone I have seen does.  And I'm sure it would be a safe assumption that any colt rifle you buy will have the proper height in the FSB.

Quoted: home.comcast.net/~gocartmozart/front_sight_base2.jpg

Excellent picture!  I"m wondering what the height difference is between the two, from the top of the barrel to the flat, horizontal part between the ears.

I have a flat top from J&T and it appears to have just a standard base.  

Does anyone know what Bushmaster does when you buy a flat top rifle/carbine from them along with a Bushmaster DCH? Do they use a taller front post or the F FSB?

AFAIK RRA and DPMS only use commercial spec DCHs and thus would work with any FSB combination.

Quoted: Does anyone know what Bushmaster does when you buy a flat top rifle/carbine from them along with a Bushmaster DCH? Do they use a taller front post or the F FSB? AFAIK RRA and DPMS only use commercial spec DCHs and thus would work with any FSB combination.

Having just had an argument w/the Bushmaster guy who runs their thread  on this site, a week ago, when I ordered a 16" barrel, and specified that it come w/the higher post; I'll be happy to tell you what Bushie's totally incorrect psition is.  They use the standard height front sight base AND blade on their carbines----because Colt has told them that the Colt sight unit is higher than anyones elses on the flat tops, and that's the reason for the F base.

And like the guys on this site who keep on insisting that 's the reason, he totally ignored the fact that Colt has ALWAYS had a higher front sight point on their short barrelled pieces---all the way back to the XM177 SMGs in Viet Nam.  Wouldn't respond when I pointed that out to him.

People; I've got a round profile front post, that came on the SP1 carbine I bought in 1978.  It's .040 higher than the front blades I pulled off the milsurp M16A1 upper assy I have, when I changed all my front blades to current square types. I work with a former service armorer who remembers they had to keep two heights of front sight on hand, for the occasional SMG that came through the shop in the immediate aftermath of Viet Nam

My M4gery, with a Rock River barrel  a Conti flat top upper, and a BUSHMASTER sight unit, needed a .040 higher front sight blade.  

So my word to any of you who have carbine types is, if the front sight base ain't stamped "F" on the left side, order a higher post from Buishie (part #9349056-M).  And if it ends up that you can get away w/a standard post, just screw the higher one down a few clicks, but I doubt that you'll have to,

Oh, by the way,  when I pointed out to the Bushie guy that others have posted on their thread about needing a higher post on the carbines, his response was; "You should see all the nut case idiot postings we get on that thread".  So if any of you have ever posted on that thread, now you know what the guy who runs it  thinks of you

ROFL well that answers my question. Bushmaster uses a mil-spec DCH (rear sight sits higher) which allows it to turn up to 6/3.

I am using a DPMS DCH (com-spec, can only turn up to "5" w/ IBZ) and it works fine with the Bushmaster standard A2 FSB. RRA appears to use com-spec DCHs as well.

I have some spare 0.040" taller front posts on hand but I didn't need them with my new com-spec DCHs.

I"m wondering what the height difference is between the two, from the top of the barrel to the flat, horizontal part between the ears.

~1.94" versus ~1.98"