# Low gas block height



## Chaser (Sep 28, 2007)

What is the point behind a gas block (top is flat, with picatinny rail) that sits lower than the top rail across the fore end and receiver?


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## Wind In His Hair (Dec 31, 2009)

Front sights are available in different heights. A low profile gas block would accommodate a taller front sight that would be too tall on a same plane gas block.


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## Frisco Pete (Sep 22, 2007)

If you mean a low-profile gas block that has no Picatinny/Weaver rail on top, that would be for those who want the gas block to fit under the free-float rail and plan on mounting an iron sight (BUIS) on the quad rail. A longer quad rail can be used and the result is pretty clean.

Standard gas blocks with the Picatinny/Weaver rail top are a bit lower than most quad rails. Therefore outfits that make the front irons, for example Troy Ind. offer them in both gas block and rail heights to satisfy all customers.

It is just customer/user preference.

Here is a low-profile gas block installed waiting for the quad rail to be slipped over it:









Here is an example of a Noveske/Troy front sight mounted on the rail with a low-profile gas block partially under the rail:









Same sight/rail/gas block from the side:


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## Chaser (Sep 28, 2007)

Here is what I am talking about:
[attachment=0:1odixjfx]gasblock.jpg[/attachment:1odixjfx]
The top of the picatinny rail on the gas block sits just about 3/16 of an inch lower than the top of the rail on the hand guard. I have seen sights that are taller, and I have seen spacers that bring the height up as well, although they all seem to put the front sight up too high, making it impossible to adjust the elevation of the BUIS to a position allowing them to be sighted in.


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## Chaser (Sep 28, 2007)

Perhaps a mount like this was designed to be mounted on the lower gas blocks?
http://www.cheaperthandirt.com/product/2-VLTSM-OCG


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## Frisco Pete (Sep 22, 2007)

Like I said, most good companies that make BUIS offer fronts in either gas block mount height or rail mount height.

The Weaver-style gas block came _before_ full-float quad rails became popular - of course both are available now and sometimes used in conjunction with each other. The design of the FF quad rail is such that it requires the lower sight height obviously, and reputable manufactures cater to both mounting areas in height with 2 front sights heights in order to maintain a standard.

However you may have to do a little digging to make sure the one you order is the appropriate height.
On the other hand, the pictured AR could use either height as it has a mounting place for both.

As mentioned, the lower gas block type came out BEFORE they really had FF quad rails. My AWB-era Rock River had that option. There was no FF quads then. That is the key to the question. It is not stupid, just the way of AR evolution.


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## Chaser (Sep 28, 2007)

Ok, I understand. I did look on the Diamondhead website, and saw that they make taller BUIS, but they are too dang expensive. More than the front and back MBUS combined. Guess I'll just run the front one where I have it now.


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