# Need gas block help



## MikeH (Jul 14, 2009)

i have a bushmaster AR with a flat top upper, but i want to add a gas block with a picatinny rail instead of the smooth one thats on there now. im not sure which size diameter gas block i need. they make a .6xx,.7xx, and .9xx. also i want to know if anybody around here can do the swap. i would rather pay somebody who knows what they are doing to change it, instead of me messing with it for hours and risking me messing something up. thanks in advance for any and all info


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## ABailey (May 25, 2010)

Those numbers come from what profile your barrel is. If unsure, you would need a set of calipers to tell. Edit* most .223/5.56 are .750


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## bigbulls (Mar 12, 2008)

Which flat top bushmaster do you have?

If you have a standard military M4 profile barrel (#9 in the pic and pretty typical on most AR's) then you would need the gas block with the .750" ID.


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## MikeH (Jul 14, 2009)

yes it is the standard m4 carbine barrel but it dosent have the front sight, just a smooth gas block. now that i know which one to get, i really want to find somebody very knowledgable in doing this swap for me..i dont mind paying!


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## MULLET HUNTER (Oct 3, 2007)

MikeH said:


> yes it is the standard m4 carbine barrel but it dosent have the front sight, just a smooth gas block. now that i know which one to get, i really want to find somebody very knowledgable in doing this swap for me..i dont mind paying!


Then take it to jays...


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## MikeH (Jul 14, 2009)

Ill pass on taking it to jays, thanks though


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## Gravity3694 (May 10, 2011)

You probably have a low profile gas block which are held in place by two set screws on the barrel. There are not many railed gas blocks on the market. Most of the railed blocks are not that great anyway since they are not on the same plane as the upper receiver.

If you have a low profile gas block with set screws it will not be easy to mount a reliable gas block since clamp on gas blocks are not reliable and drilling taper pins or drilling and tapping for set screws isn't that easy.

Changing gas blocks on an AR is not drop in simple, there's some work that has to done. If your willing to ship Adco does a good job on ARs. I myself can do some work on ARs, but I'm limited due to a lack of a vice, drill press and drill jigs.

Post pics and I can see what I can do.


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## glassplus (May 6, 2009)

pm sent


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## outlaw (Feb 12, 2012)

It sounds like you have a Bushmaster ORC?

I have the same rifle and planned to change out my gas block as well. I don't know whether you're set on it or not, but I ended up deciding to go with a mid-length rail system like a Daniel Defense Lite 12 instead. The DD rail will install over the low-profile gas block and then of course you'll have a rail available to attach a front sight, or whatever else you wanted. 

It will be a little more expensive in the long run though, so just a heads up there.


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## Cow with Gun (Feb 11, 2012)

Go to www.ar15builder.com , go to bottom of page click -
Instructional videos
It has videos on how to build an AR from start to finish your self.
You can pick all diffrent ar parts and put together and build your own ar.


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