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Posted: 11/10/2005 10:47:10 PM EDT
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A quick and simple question, I think: What does an F or "non F" Front Sight Base mean? I hope I didn't miss a recent post on this since I did do a good search of the backposts first. Thanks, Matt |
Well, actually, they have a higher front sight MOUNTING SHELF; .040 inch higher to be exact. That's so GI armorers can use the same front sight insert for both rifles and carbines. Prior to the inception of the F marked bases, short barrel types, like the XM177E2 of Viet Nam vintage, and the later carbine and M4 types needed to have a higher front sight insert installed to be able to sight in without having the blade halfway out of the threaded hole. Now there are some folks on this sight who believe that the higher sight point is only needed on flat top type pieces. They are wrong. All short barrel ARs should have a higher front sight tip. In the "old days", the higher insert was used. My SP1 carbine came with a higher blade in 1978. I have seen posts indicating that even the M16A2 rifles being produced these days have the F marked base, which makes sense, I guess. You can always screw the sight insert down further into the base if need be; so using the F marked base only will save Colt and FN a bit of time in production, no matter which type they're turning out  The civilian shooter really doesn't need to worry a whole lot about the issue. If he has a carbine type that can't be sighted in with a standard height blade, Bushmaster sells a higher front post that gets the same thing done (part# 9349056-M) for $4.95.  BTW; The "F" marking should be stamped into the bar on the left side of the base. There are some standard type bases out there with F's forged into them as part of the forge makers code. I have one, in fact. These are standard dimension pieces. |
very interesting, thanks
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None if this "information" in red is correct. This issue is gone over every month. It has nothing to do with carbines and rifles. It has to do with fixed handles and flattops. |
The M16A2 does not use the F FSB. The F FSB is used with flat top uppers, as in the M4/A1 and the M16A4. Colt's raised the rear sight from the bore approximately .040" on their carry handles in about 1995. Shortly there after Colt's raised the front sight base to coincide with the new higher carry handle. FN follows suit because they use Colt's TDP to produce the M16A4. |
My original Colt 16" AR15-A2 Gov Carbine has the shorter post and zero perfectly (albiet a bit to the left). I have seen alot of M16A4 and M4A1 (flat top) with the F-FSB, but I have never seen a M16A2 with one? (They could be out there ? but I have never seen one) Current Mil Specs require there to be an additional 16 clicks of doward adjustment on the front sight post after the rifle has been zeroed. IIRC, the difference between the A2 and F-FSB is .032" |
| So it seems to me that since I can get a $5 extended front sight post this really shouldn't be a deciding factor in choosing a barrel for a working rifle. The barrel I'm looking at will be going on a flat top upper with ARMS #40 BUIS. Thanks so much for the replies/patience fellas, as this sounds to be a recurring question. |
I would agree. The F-FSB is a nice feature, but it be easily rectified with the $5 taller post. |
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Here is the kind of person shamayim is. He decided to send me some IMs today. "Actually, your statements about my posting on this thread are totally off the wall. When you have 30 years of experience w/the M16/AR15, including 7 years as weapons training & maintainance officer w/security as a large federal agency, I might give some credit to your opinions. 'Til thern, you're just another newbie who doesn't know half of what he thinks he knows. What I posted was correct information. Not that I expect you to believe it. After all, you've got that pretty picture of a dancing horse on your sig line. Paul G." "What the blazes are you talking about? You post on a thread that everything I've said in a response is wrong, and then respond to my note to you that M16A2s don't have F marked bases while A4s have them. Where did I ever say that A2s had F marked bases? All I posted was that recently both FN and Colt are using F bases on their rifles, as well as on M4s. If you want to fault me for not specifying that current rifle production is pretty much all flat top, feel free, but how does that make everything else I posted incorrect? Can one not achieve a higher font sight tip with an .040 higher post? Has Colt not used a higher front sight tip on every carbine/submachine gun version it ever made; initially with a higher post, and more recently with a higher F base? Sport, when you've got 25 or more years owning, using, maintaining and generally being around M16s/AR15s, I'll stop considering you a newbie. 'Till then---- have a nice day. Paul G."
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