I am going to build a tricked out rifle... any reason to go with a fixed FSB instead of a gas block with a flip up front sight?  It seems like the flip up is better in case I decide to mount an ACOG or some other traditional scope.  Also, I have never used a cowitnessed red dot so I'm not sure I'd like the front post in the sight picture with a red dot.

Perhaps it would be best to use a gas block with a weaver rail so I could either use one of the flip-ups or the more conventional detachable front sights that looks very similar to the fixed FSB.

I have three done with the YHM flip ups.  Two built into the gas block and one that clamps on.  I see no disadvantage.  Some will say on a combat rifle a GB/GBFS that attaches with set screws is a liability because if bumped hard enough it "could" turn, but mine are not on combat rifles and I know damned good and well they never will be.  I do not play pretend soldier or plan my life and builds around unlikely SHTF scenarios so the set screw gas blocks work just fine for me (not knocking those who do, but that is not what I build for).
Another reason I like them is they are out of the way when using whatever optic system I might have on there and yet they co-witness perfectly the same as with a fixed FS tower.

Man, I was just fixing to post the same question.  Free Bump.  Anyone Else??

Has anyone had problems with screwed-on gas blocks coming loose?  Are they really set screws or does the screw go thru the pin hole?  Do they make pinned on gas blocks?

The ones I have are held on by two set screws.  I have two gas block flip up front sights(YHM) which use two set screws and two DPMS gas blocks, one 4 rail and one single rail, and both use two set screws.  They are just normal set screws that bite into the barrel steel.  The YHM flip up front sight gas block can be pinned in place but you will have to drill both the block and the barrel.  The set screws hold just fine for my uses.  My .458 SOCOM uses a single rail gas block, set screw, and it has yet to budge.

The whole scenario of these bases being "bumped" and thereby "turned" is one of those enduring myths that some seem to obsess over but are never documented. If mounted properly, they will not "turn" if "bumped".

The folding front sight/gas block is a good thing and an inevitable advance in the evolution of the AR. One just needs to go back to the Colt ACR project to see the changes that will come when the obstinant resistance of overly conservative minds is finally overcome: a non-carbine with a telestock, flat-top, optics, and folding rear AND front sights. All but the last are now or will shortly be Standard, and the mossbacks will quietly join the future, or be passed by.

... slingin' beans at mess!

I'm running the GGG flip up fron on my AR10's gas block rail, and it is rock solid.  I have no concerns about it working its way loose or anything.  It would take just a little longer to get it into action, but not so long as to really matter, IMHO.

I think the Armalite gas block is a clamp on unit as opposed to using set screws.  This seems much better to me.

good question, Nevada.

I have wondered the same thing before.

I would add a question to consider and that is.......... are they a reliable height?

That is with Colt FSB height being different than others, can you simply mount a flipper on a rail and expect it to be the proper height?


anyone?

Hi Nevada,  I have an LMT fixed BUIS and an EoTech 552.  I have tried this combo on two uppers, a CMT with a quard rail gas block and a YHM flip up, and an LMT with mil spec front sight tower (same height as Colt).  No problem on co witnessing on either upper, the red dot is right on top of the sight post.  I have no problem with the sight picture.  With the larger apeture and both eyes open, it is a very fast combo for acquiring a target.  When I switched the sights from the CMT to the LMT with the higher front sight, I did have to change the elevation.

As bookhound pointed out you first need to answer the question "What's it for?" The current generation of flip-up iron sights is so mature that, properly selected and properly installed, reliabilitiy is a moot issue. That is; if you've encountered an event profound enough to screw up that front sight, the front sight is probably the least of your worries.

So then it comes down to a matter of your most likely deployment of the rifle: If you're most likely to employ it as a stand-off device, then being able to keep the front sight out of the way unless needed seems a plus.

However, if you see CQB (a euphemism for "Kick em' in the balls and shoot em' in the face.") as the most likely application: If you need those BACKUP iron sights, you're going to need them right fXXXin now! Unlike a flip-up rear sight, the time it takes to dismount the rifle from your shoulder, flip the front sight, re-mount the rifle, and re-acquire your target are going to seem like an eternity.

Think it through Choose wisely.

SD

Quoted: Keep in mind any magnified scope at 4 or greater power will "look through" the front sight base.

What about a 3.5X ACOG on a rifle length sight radius?