Hey all, I have an issue in a previous thread that I don't think anyone is paying attention to anymore, but I think I've identified that I need a F spaced Front Iron.

Here's the thread if you want to know more:
www.ar15.com/forums/topic.html?b=3&f=66&t=343496

Basically I have an A3 flat top and with my carry handle I can't adjust my front iron post any higher, but a taller front post will make it stick out above the iron itself. So an F iron should take care of my issue.

I looked at my Stag Arms 20" A3 and the front Iron has a CROWN looking symbol on it. So it's not already F marked right??

Also, I'm trying to find a replacement online, I've only found one on Bravo Company's site but they're out of stock. Plus I need to replace the flash hider, which will suck because I've never done that before...

Any help would rock, sorry for the new topic but my old one is beat.

Brock

Son of a bitch... I hate that crap... bah, will call them tomorrow! You don't think they'll just send me a carry handle do you?

Thanks!

A taller front sight post in a standard FSB will give the exact same sight picture.







There are two variations of the front sight base but there are also two variations of the carry handle.

The “F” marked front sight base is the exact same sight base as the non marked, the only difference is the shelf is .040 inches higher as it simply is not machined down the extra .040. With the extended sight post (+.040) on a standard sight base you get the exact same sight picture as with the “F” marked sight base and a standard sight post.

There are two variations of the carry handle. If you look at the “mil-spec” handle the contour of the handle matches the contour of the rear sight base and the shelf height is measured around .835 inches. This is the handle for the “F” marked sight base.

The second carry handle has a lower rear sight. If you look at the contour of the handle you will notice that the sight sits about .040 inches lower and the shelf height is about .795 inches. This is the commercial height handle for use with a standard front sight base and is used by Bushy, DPMS, etc.

If you mis match the non “F” marked front sight with a mil-spec carry handle you may not be able to screw the sight pin high enough to match the higher carry handle rear sight. The solution is a .040 higher front sight pin.

I am new to ARs and this forum but I am also having some problems with the front sight post.  I bought a cheaper AR for my first one until I figure out what I really want.  I bought a 16" carbine from CMMG.  It is one they put together from a kit I believe.  It is a DPMS lower and I guess the rest of the upper is the kit.  It has a detachable carry handle and on the front sight base there is an F.  I tried to sight it in at 25yds and had to raise the front sight more than I think I should.  If I sight it in for 50 yds it is really high, I can see a gap between the base of the sight and the sight base.  I just got an extended front sight post from bushmaster and it seems to do the trick even though I have not been back to the range with it.  Is this normal?  Should I need an extended post if I have a front sight base with an F on it?  Other than that it seems to shoot really tight groups and I have had no failures.

Originally Posted By Matt15: I am new to ARs and this forum but I am also having some problems with the front sight post.  I bought a cheaper AR for my first one until I figure out what I really want.  I bought a 16" carbine from CMMG.  It is one they put together from a kit I believe.  It is a DPMS lower and I guess the rest of the upper is the kit.  It has a detachable carry handle and on the front sight base there is an F.  I tried to sight it in at 25yds and had to raise the front sight more than I think I should.  If I sight it in for 50 yds it is really high, I can see a gap between the base of the sight and the sight base.  I just got an extended front sight post from bushmaster and it seems to do the trick even though I have not been back to the range with it.  Is this normal?  Should I need an extended post if I have a front sight base with an F on it?  Other than that it seems to shoot really tight groups and I have had no failures.

Is the "F" mark hand stamped on the left side?  I have seen some CMMG that are commercial height and not mill spec so it may very well be that you would have to use the higher sight post for a proper zero.

hey guys, i got the .040 front site post from BM for my FSB its not that much taller than the original so it doenst sit too high in the base and it worked like a charm.
                     for what its worth.

Those KNS front sight pin kits are great too. They have the standard height and .040 taller pins included. They have the regular square post pins, reduced-size square post pins, bead-style pins, and a v-notch pin which I really like. I have the crown FSB on my bushmaster upper and needed the .040" taller pin for it to work with my #40-L. I used the remaining pins in the kit on my 6.8spc upper and my .458S upper. The 6.8spc wears a small beaded pin which was painted hi-vis green, and for now the .458S uses the v-notched post in a MI front sight  for railed gas blocks. The v-notch is great for long-range targets since it doesn't obscure your sight picture.

Taller post is the best fix

Would the opposite also hold true if you used an "F" marked FSB and a commercial carry handle? Would the front sight post would be too tall, even a mil-spec post?
I recently ran into exactly that same situation using an M&A upper with an "F" FSB and a Cardinal Forge carry handle. I had to nearly bottom out the front sight post in the base to get a zero.

If you run out of room you can always remove material from the top of the sight post.
Dustin

It seems this is the right place to ask with the information posted on FSBs.  

I do not have a lot of experience with RRA or the respective parts but am familiar with other manufacturers  such as LMT; LWRC....  

I have a RRA NM fsb and it seems the taper pin pre-drilled holes only line up with RRA barrels.    I have changed & cut plenty of fsb's but have not encountered this particular issue.  I have checked it on a FN barrel with no-go and a custom barrel from the FT Bragg area with no-go.  Can you please confirm if this is factual or advise on barrels to use RRA fsb?

Any information or direction provided is greatly appreciated.  Thanks in advance.

I've never owned one but don't the RRA NM FSB's have set screws to be tightened on the "flats" of the NM barrels and not taper pins? I would guess if this is the case they would only fit a barrel with the "flat spots" like a NM barrel.

Its actually two chrome pins that are not taper pins.  I am pretty sure this is from a chrome barrel assembly.  One actually snapped really easily and that was when I thought it was a good indication that I should stop what I was doing.  

Thanks for replying.

This thread was so helpful.  I need to get a friggin new front sight post.  I was wondering why my BM MOE Dissipator clone didn't want to let me set a BZ0.

I just went through this two weeks ago - a new 20" flat top upper with a standard rifle FSB, and a removable carry handle clamp-on rear sight which shot high - about 3 inches at 50 yards, which is about 6 MOA.  6 MOA should require .036" of sight movement to zero it.  I bought an 0.040 taller front sight post.  Note that 0.040" is less than 7 human hairs.  It did not extend above the protective ears of the FSB, even with the base of the sight post even with the deck of the FSB..

just buy the .040 front post from bushmaster.com its like 6 bucks that will give you the same height as the f marked base

I had to nearly bottom out the front sight post in the base to get a zero

I use well its probably the same bushmaster one from Windham weaponry and they work great.

Its a pain and can get expensive to drill and switch out a new fsb to a f marked one when all you need to do is change out the $6 front post and it will be good to go

I have a FSB with markings "D 98 'R1' (with a circle around it) 2"
Never saw that before.
Anyone know what these marking mean?