I put this in the Optics/Sights page but did not get any replies so I am reposting it here.  Sorry for the trouble...  I am planning on building a new "all-around" AR so of course I got out the Brownells Bible. I just buy complete uppers and do the lowers myself. Anyway, on pg 1 they have the DPMS uppers with the stainless bull barrels. My question is does anyone know what gas block comes on them i.e. does it have rails to mount a flip of front sight or not. And if it does not have rails how hard is it to replace it with one that does. Sorry for the long post. Thanks in advance.

First, the gas block that DPMS installs on their barrels dont provide any means of mounting anything to them. According to Brownell's catalog, the Super Bull barrel from DPMS is 1.08" @ the muzzle. I don't think anybody makes a picatinny rail gas block that fits barrels of that diameter.  On the other hand if you get a barrel that is .936" dia. (like the DPMS varmint barrel), there are a few available from different vendors as well as DPMS.  

OK I called Brownells and spoke with a Tech guy.  He said that part #231-000-019 is not the super bull just the bull and is .925 at the muzzle.  He also stated it is held in place by a single set screw.  Now DPMS has a four rail gas block but it says it is .936 and uses two set screws.  I is possible for me to switch to this one and is it as simple as unscrewing one sliding it off and screwing on the other or is there other things you have to do.  And since the diameter is not the same will it still work.  Thanks I'm new to trying to build uppers.

Maverick,

Go for it. The 4 Rail .936" gas block works fine on the DPMS Bull Barrel. I have two of them.

TW

I have one of their bull barrels right here.  It is 1.050" under the handguards, .935" at the gas block section, and then tapers from .906" just foward of the gas block, to .890" at the muzzle.

They probably intended the forward section of the barrel to be a straight cylinder but had the tailstock on the lathe .008" too far inboard compared to the headstock, hence the .016" taper at the muzzle.

Tony Rumore
Tromix Corp

Thanks for the replies guys but can someone possibly explain how to swap out gas blocks?  I have never done that before, all I know is there are two set screws so is it as simple as unscrewing it and sliding the new one on or do I have adjust any thing or bend or twirl around in circles to make something fit?

Yes, just loosen the set screws, slide the "old" one off and repeat in reverse with the "new" one. Just make sure you keep it aligned using the the gas tube as a gage (the tube goes into the upper receiver straight...not at an angle).