I have what may be the dumbest question of all dumb questions. I have been trying to zero my iron sights, even with the front post bottomed out, it still prints very low. I have recently read that there is such a thing as gas block sights and inline sights. The hand guard on my rifle is level with the receiver to the muzzle. Front sight would not mount to the gas block. Is this such a thing? If so, can some recommend sights. Or am I doing something wrong? Thank you in advance for your help.

Yes, there are two types of rail mount front sights for AR rifles. One type mounts to a rail that extends level from the receiver, and the second is for mounting on gas blocks. The mounting rail on top of the gas block I have on one rifle is significantly lower than the rail on top of the receiver, and the iron sight base must be higher to adjust for that.

It’s something I discovered myself only after I had ordered the wrong front sight after replacing a barrel. I had seen a small print mention of a difference, but I didn’t understand it at the time. For some reason the issue doesn’t seem to be emphasized very much in descriptions of the different sights. If it is, and as I say, I did not pick up on it.

If you have a tall gas block sight like mine and mount it level with the rear sight on the receiver rail, then I would expect it to give you a very low POI.

There are also different height front sites available. The normal issue is needing more height, but I guess the opposite can also be true. Assuming your rear site is something standard for an AR absent other issues you can also easily modify yours.

If the handguard is level, you might have an issue with your barrel installation - an over torqued barrel nut maybe?

Also, what kind of sights?

Perhaps there are front sights designed for very tall gas blocks, but I didn’t run across anything like that when trying to figure out what my issue was. Normally a gas block wouldn’t have to be any taller than for the gas tube to fit into it, and I can’t think of another reason for it to be higher than necessary. If the gas block was made taller than necessary for the gas tube interface, I’d expect it to be the same height as the receiver rail, and no higher.

Based on further research, now with some clues from you all; I think what I need are "same plane" sights.

Nope. Same plane has nothing to do with your problem.

Same plane means the small and large aperture shoot to exactly the same point of impact. On military sights and others, the small aperture is the distance sight, so it incorporates some elevation into it. Meaning if you shoot a target at 50 yards with the large aperture, then switch to the small aperture, they will not be shooting the same centered group.

Why don’t you give us more information? What brand rifle, what handguard, is it factory built or did you build it yourself , what brand sights are you using???

The problem you need to solve is actually a very simple one. If the rail your front sight bolts on to is the same heighth as the rail on the top of the upper receiver, you need the shorter front sight. If the rail your front sight goes on is lower than the rail on top of your receiver, then you need the taller front sight. It sounds like you're on the right track when you think in terms of sights that are sitting on rails that are level with each other. That's actually the more common option; you'd generally have to look for the taller front sights.

ETA: For what it's worth, Midwest Industries just calls their taller front sights "Gas Block" models (4th row down). http://www.midwestindustriesin...ont-Sights-s/245.htm

I don't exactly get the setup involved. But there are plenty of people (I normally use Troy) that makes sights intended for a monolithic rail (meaning the whole shebang is on the same plane, think HK 416 or SCAR). This has nothing to do with the aperture issue discussed above for std. GI sights. So to help it would be nice to have some sense of the situation as bubbatime asks.

quote:

Originally posted by bubbatime:
Nope. Same plane has nothing to do with your problem.

Of course it does as described by the topic starter:

quote:

Originally posted by dan03833:
The hand guard on my rifle is level with the receiver to the muzzle. Front sight would not mount to the gas block.

If the top of the gas block is ~1/4 inch below the top of the receiver rail where the rear sight is mounted (as mine is), that’s a very large difference for the front sight adjustment to make up, and probably impossible by itself. When using a gas block-mounted sight, it must be ~1/4" taller to make up that difference.

A sight that’s designed to work on the same plane as the rear sight would be necessary for his setup (see “level” and “front sight would not mount to the gas block” above). If he is using a taller front sight that was designed for use on the gas block, but is mounted on the same plane as the rear sight, the gun will shoot very low—just as he described.