I’ve got FSPs on all my rifles now but I’ve got a LW middy upper waiting to be set it up for general purpose/HD carbine with RDS and fixed rear.
what is your preference of a FSP vs. Rail mount front sight and why?
are there significant differences in weight between FSP and rail mount and gas block?
other issues? (rail choice, hand placement, cost)…
A rail mounted front sight won’t get hot and burn you. You can flip it down to get out of the way of optics.
On the other hand, if you run a free floated barrel for accuracy and want the best from iron sights, your front iron needs to be on that barrel. A rail or tube mounted front sight moves independently of the barrel, and you’ll end up losing the benefit of being free floated. Of course, outside of NRA High Power and Service Rifles, sub-optimal back up iron sights aren’t really a problem.
kartoffel pretty much covered it. personally, i’m a big fan of FSPs. they don’t bother me, and if the S ever REALLY HTF, i’m good out to 500m with irons. i even did a fixed FSB on my SPR (gasp!).
only disadvantage is that they’re heavier… a rail mounted sight actually saves weight, so long as you use a light rail and a light sight.
yes, I see what you mean about FF rails and sights. I really haven’t considered using folding sights on a rail. that just seems like too much monkey and not enough football. I’d go with a fixed sight like the DD if I decide to do a rail mount.
I’ve got all FSPs but I see a lot of people going to rail mounts lately… like the current uptick in interest in 14.5 barrels. I wondered if there was anything to it other than it’s the new setup du-jour…
is it really lighter if you add in the weight of the gas block?
Yes, it is really lighter. The FSB is a relatively heavy casting, and even cutting down the stock piece (the best low-profile gas block on the market IMHO) and shaving it you’re saving a lot of weight relatively speaking.
What we’re talking about here isn’t metric tons by any means. But, with the right rail/gas-block/BUIS you can certainly come in at 1:1 with the FSB/handguard setup. Add in something like the MI FSB mount to attach a light and the difference is even greater. I don’t think it’s correct to simply compare FSB & M4 handguards to a rail system with flipup sight as you’re not comparing capability:capability.
add 2.8 oz for DD BUIS front & rear
add 2.8 oz for DD BUIS front & rear
excellent info, thanks Rob…
are those all carbine uppers in the photos? what rail is that in the bottom pic?
Those are all Colt 6933 uppers with 11.5" .625" dia. barrels with carbine-length gas systems. Last rail is a Daniel Defense M4 9.0.
My front sight is rail-mounted and fixed. I’m presuming you’re referring to rail-mounted, flip-up front sights?
I prefer a fixed front sight and flip-up rear sight. I don’t want to have to reach out to the long end of the rifle to flip up a front BUIS in an emergency.
no. FSP vs. rail mounted sights. FSP is the standard pinned on front sight on the AR platform. rail mount sights, whether folding or fixed, are mounted to a railed handguard.
personally, I agree that a front sight should be fixed whether FSP or rail mount unless there are specific reasons for it not to be. I can’t think of any reason for that, though…
Rob has shown that the combination of a gas block, 2" longer rail, and railmount front sight should still be somewhat lighter than a FSP and shorter rail system, though close to 1:1. the issue then becomes less about weight than the utility of an extended rail for hand position and accessories like lights, VFGs, etc…
I prefer midlengths to carbines with a 16" barrel and the setup of a FSP and 9" rail works well for my uses. my one carbine, a DDM4 has the Omega X™ 12.0 FSP Rail System.
I’m not especially thrilled with this as the FSP protrudes through the rail in exactly the place I rest my support hand thumb. I may sell this rail and replace it with a gasblock, 11" rail, and rail mount sight, or I might sell the whole upper and start over. the jury is still out…
Ok, I’m tracking with you now. I’m used to the reference FSB (front sight base) for what you’re referring to as the FSP.
Were I to purchase a new upper, I’d opt for a BCM 16" lightweight mid-length and attach a DD Lite 12 rail. I’d mount a DD rail-mounted, fixed front sight, leaving enough room to mount a light at 12:00, in front of the front sight.
ah, gotcha… I’ve always heard of the FSP as the Front Sight Post. anyway…
I do track your choice of uppers, though, as I’ve been swaying a little to that music myself…
Just as a little clarification, “FSP” usually means the little “post” at the top that screws up and down to adjust for elevation while “FSB” usually means the large, cast, “A-frame” assembly. FWIW
ra2bach you’ve pretty much hit on exactly the issue. Depending on hardware chosen you can get a longer handguard, with rails to mount accessories to, and a clamp-on front BUIS over a low-profile gas block well within the same weight for a standard FSB and either plastic handguards or rail behind it. What it essentially comes down to is that in most cases 2" of rail weighs about the same as the weight savings of FSB vs. BUIS/gas-block. To try to illustrate…
FSB: 4.5 oz - GB: 1.4 - BUIS: 1.5 = 1.6 oz saved
TRX 11.0: 9.93 oz - TRX 9.0: 8.46 oz = 1.47 oz gained
Net difference is less than 0.20 oz. It should be noted that more weight can be saved by chopping, shaving, and halving the stock FSB to be held on with only one pin, and that some FSBs may weigh even more than the 4.5 oz quoted, so these are rough numbers and there may be some deviation in different applications.
Personally, if I had decided to go with a rail system anyway, and the TRX Extreme in particular, I see no reason to go with the 9.0 behind an FSB and would instead opt for the 11.0 over the chopped FSB.
FSBs are forged, by the way…
^^^^^
Good FSBs are forged. I had a DPMS upper in my youth that had a cast unit.
ah, now I see. sorry for the confusion guys… nomenclature is not my strong suit and I was taking FSP from the DD literature for a rail that allowed the FSB to protrude through the top of the rail.
at any rate, I think I see my direction now. I still have a preference for pinned FSB’s but I do understand the attraction/benefits of a gasblock/longer rail/ rail mount sight, especially on a carbine length gas system where the FSB is exactly where I want to put my hand.
I’m even seeing the benefit on a longer gas system like a midlength where the FSB pushes the weight further toward the muzzle. a 16" govt. profile middie with FSB and 9" rail is no lightweight. I’ve been using Emod stocks to balance the forward weight bias but I’d like to bring the whole thing back down in weight. at the end of a long training day I feel like the guy at the bottom of the ladder who has been loading bales of roofing shingles on the elevator… :lazy:
and this is what prompted my question - I’m thinking I’m going to chop one of my middies to 14.5, shave the FSB, and go with a longer rail. now the big question - TRX or VTAC Extreme??? 
i haven’t seen a cast FSB in many o’ long year… DPMS would be the one to hold on to that failed endeavor the longest, though. colt stopped casting 'em in the 60s, as i recall.