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unclekuster
September 29, 2012, 09:58 AM
I got an AR I'd like to change a little, and the front sight doesn't work for me.
So I need a low profile gas block. Question(s) is: why would i need an "adjustable" gas block, and is it worth the extra cost ?

Regolith
September 29, 2012, 11:40 AM
An adjustable gas block lets you tune the gas system to the loads you're using. With hotter loads you'd close up the aperture a bit to keep your brass from being tossed into the next county, and with softer loads you'd open it up so it will cycle more reliably. Or you could close it completely to turn it into a single shot/straight pull bolt action.

It's a fairly popular mod for Mini-14s, as they tend to have problems with chucking brass all the way across the range, but I haven't heard of them being used with AR-15s all that much.

It may be worth buying if you plan on mounting a suppressor any time in the future, as closing the gas system helps keep the noise down or you can open it up and cycle subsonic loads better, but other than that it's not really all that necessary, unless you absolutely hate chasing brass down.

DnPRK
September 29, 2012, 09:52 PM
A gas-operated rifle balances gas port pressure against the sprung weight of the bolt carrier/buffer group. Using ammo with the wrong burning rate powder, or if your barrel's gas port is the wrong size will throw that balance out of whack. The result is failure to extract or failure to feed.

If your rifles cycles reliably with good ammo, you don't need an adjustable gas block.

Powderman
September 29, 2012, 10:09 PM
Also--if you have a front sight/gas block that is pinned in place, you're going to have a devil of a time getting it off. Those pins are swaged in under tremendous pressure.

bedlamite
September 29, 2012, 10:21 PM
Adjustable blocks on AR-15's are more common with supressor, but usually not necessary otherwise. You can usually tune the system with different weight bolts, buffers, and springs.

Also--if you have a front sight/gas block that is pinned in place, you're going to have a devil of a time getting it off. Those pins are swaged in under tremendous pressure.

Actually, it's very easy. (http://www.youtube.com/watch?v=ZOA0jA0Ei74)

Quentin2
September 29, 2012, 11:30 PM
A lot of folks just cut down the standard A2 sight leaving a nice low profile gas block. As has been mentioned above, those things are really on there so why not retain the gas block portion. A longer rail will cover up your handywork.

madcratebuilder
September 30, 2012, 06:29 AM
Question(s) is: why would i need an "adjustable" gas block, and is it worth the extra cost ?

Only if you plan on using a suppressor.

It's easy to cut the sight block you have, a search should find you many diy's.

Powderman
September 30, 2012, 05:19 PM
Bedlamite--you might want to read the comments under that YouTube video--which oversimplifies the process greatly.

Have you tried to remove the FSB pins from a Colt front sight base? It's not easy. Trust me on this one.