Front sights sticking way up

[Ned Christiansen]

I was surprised to hear someone asking for a higher rear sight. I frequently see guns in need of a lower rear sight. I guess we're talking about two different things here but this phenomenon has become a major frustration for me. Here's what I see:

The carbine won't sight in until the front sight is dialed up so high that it's sticking up above the front sight base's protective ears. It's sitting there waiting to rip flesh or hook on something and get bent. This is always on a flattop carbine, and the front sights are either standard units or on some cases flip ups-- but usually standard ones. I never get to do a really in-depth exam of the gun, but my suspects are:
-Manufacturers who don't know that there are two different heights of front sight base, and/or they get them mixed up (short handguard guns should get the higher one).
-Some flattop uppers have a rail that is higher and some are lower.
-Some BUIS are higher or lower and incompatible with certain setups.

I sometimes am able to cure half the problem using the Bushmaster extra-high front sight post-- at least this gets the flange down far enough to contact the detent, and the threaded part is in deep enough that the post doesn't wobble side to side too bad-- but the post tip still sticks up beyond the protective ears.

Anybody got the real answer on this?

[jmart]

My BM tall post sticks up higher but still is below the ears (16" barrel). But not by much.

The real answer is standardized F-marked FSBs. But not all mfg's want to stock two different parts.

Like you suggest, maybe the answer is a standardized lower rear BUIS or an elevation-adjustable rear BUIS since the majority of BUIS's probably end up on flattop carbines. I just don't know.

[rob_s]

I thought BM sold two carryhandles, one for their incorrect FSB and one for the proper "F" FSB.

[jmart]

I had no problem with my supplied carry handle. But when I removed it and replaced it with a G&R Tactical-sourced LaRue BUIS I ran into the problem Ned mentions above. I could still get it to zero, but I had the post backed out so far it would wiggle and you could see daylight in between the FSB and the post's base. Not terribly comforting.

I purchased the taller front post and problem solved.

[DevilDog]

As a general rule, getting the longer front sight post for any short Bushmaster FSB (or any other make - I'm not aware of others) seems to me to be the thing to do.

I put the longer front sight post on both my 16" Bushmaster uppers and I can make them work for either my Bushmaster carry handle or my ARMS or LMT rear buis. For the Bushmaster carry handle, it will need to be turned down a bit to get a zero.

IMHO, there never should have been two sizes of FSB. I guess it was Colt that started it when they made detachable carry handles and M4's (I'm not real sure here). The second mistake was when the other manufacturer(s) (Bushmaster and ???) came along and didn't want to conform to using a taller FSB for flat tops.

Now it is just a bit of a buis-mess. Oh well... :(

[MSU721]

Ned,

I feel your pain, I'd be nice to have some consistency across the industry but is doesn't seem to happen.

This yet another great reason the BCM uppers such a great deal.

JWR

[Diz]

I had the same problem with my carbines. Both had A2 FSB's and the front sights had to be backed out too far to zero. So I went with the taller front sights for awhile but thought they looked really gay. Ended up getting a BCM upper. It solved this problem with a "F" marked FSB, and gave me all the mil-spec features I've always wanted. Once my primary carbine has been upgraded with this upper, and a CMT MPI-tested BCG, I plan on doing the same thing with my secondary.

[CapnCrunch]

I had the same problem with my carbines. Both had A2 FSB's and the front sights had to be backed out too far to zero. So I went with the taller front sights for awhile but thought they looked really gay. Ended up getting a BCM upper. It solved this problem with a "F" marked FSB, and gave me all the mil-spec features I've always wanted. Once my primary carbine has been upgraded with this upper, and a CMT MPI-tested BCG, I plan on doing the same thing with my secondary.
First of all, Brother Diz, welcome aboard! Great to see you're alive and kicking :)

And on topic: It's all about using the proper FSBs like Colt, BCM, and LMT do. When you consider what all you're getting for the price, the BCM uppers are a steal.