Posted: 6/12/2014 5:28:46 PM EDT
| On the Colt AR15A4 there seems to be some confusion on whether he FSB should be F marked or not like the carbines. Most of the discussion I have seen relates to whether it matters for a 20". Colt customer service must have received calls on this since they had a ready but not great answer. The Colt answer I received is that the FSB you get depends on the box they pull it from-- some are marked and some are not. Colt emphasized without greater explanation that whichever one you got would be correct for that rifle, including saying something that the unmarked ones were different in design but that the front sight post would be in the same place. Can anybody confirm or explain? Are they milling an unmarked base with a higher deck or just relying on the sight radius being longer such that most will not care, which also really ignores my question. I have seen measurements of F marked and unmarked FSBs but it sounds like they would both have to come off a Colt AR15A4 to confirm. |
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Quoted:
Doesnt FN USA make the now A4? 
Colt makes an AR15A4, which is basically just a Colt AR15 with a 20" gov't profile barrel and a flat-top - to mimic the M16A4 (Just like how Colt renamed the 6920 Law Enforcement Carbine to the 6920 M4 Carbine). FN Herstal makes an AR15 now with both the M4 and M16A4 likeness. FNMI makes the M16A4. I believe Colt made a few as well |
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Wait... Why one Earth would they even have non-F-marked FSB's anymore? I don't believe they make any with A2 or A1 uppers? The only difference between the F-marked and non-F-marked is the machined slot between the wings where the sight post goes.
I wouldn't imagine that they WOULDN'T have the F-marked variant; the A4 designation means that it has a flat top upper receiver, just like the M16-A4, which has an F-marked FSB. Makes sense, right? It's a legit A4 upper, should have an F-marked FSB. |
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The carbine length flattop requires a 'F' height FSB, but it's not as critical on the rifle length flattop.
There are already several thread on this subject, and emperical data from several people who own the AR15A4 without an 'F' marked FSB. They have all reported. O issues with zeroing the rifle. |
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Quoted:
I guess part of my broader question is what is Colt doing if what you get depends on what box of FSBs is in front of them. Did they decide that it doesn't matter and just use what is on hand. They've been doing that for years, although it's less common recently. I have two R6601's from 1992, one has grey receivers, non-fenced lower with no sear block and a large front pin, and a C-bolt carrier, the other has black receivers, fenced lower with standard front pin and a pinned sear block, and a standard semi-auto carrier. Same model, bought within days of each other. They just used what they had available. Bottom line though, until we get absolute confirmation that they use both or one or the other, it's just speculation. I have a feeling that they are all F-marked, but I'm willing to be informed otherwise if you present proof. 
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Quoted:
Doesnt FN USA make the now A4? I'm a Colt guy but I bought a FNH FN15 Rifle last night anyway below is what it has on it. 
- Barrel is gov't profile, chrome lined, broach rifled, stamped w/ FNH (logo) MP 1/7 5.56 NATO and with "F" marked FSB. - Bolt is marked HPT/MPI with a unmarked carrier that is chrome lined with staked gas key. - Upper receiver is from Cerro Forge, T marked, w/o FN's F stamped, M4 feed ramps, w/MilSpec carry handle. - Lower receiver is from Cerro Forge, unblocked, low shelf with selector stops. - Roll mark is plain looking with just "Model FN15", "Caliber Multi", Serial # and the FNH logo is on the mag fence area. |
| I picked up one today and inspected it at an authorized dealer and checked for all the inspection marks, M16 BCG, feed ramps, M4 upper mark, etc. and no, say again, no "F" marked FSB. I even asked the sales person to verify that I was not missing something. I did not take a picture, but is was the real Colt deal with no F-marked FSB. That is when I called Colt to try and get the company line instead of speculating. The customer service person seemed to indicate that there could be both and that both had different measurements, but that the non-F marked FSB was designed/redesigned to be proper for that model (i.e., 20" with flattop). She seemed to think that it would be more common to not get the F-marked FSB now with ramped p production, but that the assembly process could result in either part being used, but insisting that both were still correct. I could not get a direct response to why. |
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Quoted:
I picked up one today and inspected it at an authorized dealer and checked for all the inspection marks, M16 BCG, feed ramps, M4 upper mark, etc. and no, say again, no "F" marked FSB. I even asked the sales person to verify that I was not missing something. I did not take a picture, but is was the real Colt deal with no F-marked FSB. That is when I called Colt to try and get the company line instead of speculating. The customer service person seemed to indicate that there could be both and that both had different measurements, but that the non-F marked FSB was designed/redesigned to be proper for that model (i.e., 20" with flattop). She seemed to think that it would be more common to not get the F-marked FSB now with ramped p production, but that the assembly process could result in either part being used, but insisting that both were still correct. I could not get a direct response to why. That seems odd I've had owned 2 new MT6700 one in 2000 and the other in 2009 and both had the F marked FSB. Do you think the carry handle was mil spec or was it the shorter style like DPMS uses ? I have tried a mil spec carry handle on a flat top with a 20" barrel that had a A2 FSB and the front sight post needed to be raised to zero it. |
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Quoted:
So did colt install a f marked front sight base for you? When I first talked to the sales rep he said they would replace the sight then when I got it back no new sight just A note from the gunsmith that said the firearm zeroed with no issues. Like I said my 6720 did not come with A F marked sight either. |