AR-15 gas tube question

[SwampThing762]

I have recently purchased a Smith and Wesson M&P-15 Sport with the 16 inch barrel.   It currently has a carbine handguard, and I wish to replace it with a mid-length handguard.    I assume that it also has a carbine length gas tube, as well.    My question is as follows:

Is there a manufacturer for mid-length gas tubes, or do I have to buy a rifle gas tube, and cut to mid-length?   

Thanks, guys.

ST762

[Lloyd Smale]

If you have a fixed post front sight just cut the top off of it leaving the part the gas tube goes in. If you have a gas block that doesnt have a sight leave it as is. the mid sized forearm should fit right over top of it eaither way if your using a full floated forearm.

[cjclemens]

The gas tube has to match the distance from the gas block to the upper receiver.  If you want to switch to a mid-length gas tube, you need to put a mid-length barrel on it, too.  Like Lloyd said, some companies make low profile gas blocks so you can fit a mid length free-float tube over it, but it will have to be a free-float tube - a standard handguard wont work.

[SwampThing762]

My rifle has the standard A2 front sight.  It also has a standard style 2 piece handguard and a steel gas tube. 
Based on this information, can I simply switch out the parts, or is the process more involved?   I appreciate your patience and information.

ST762

[Dezynco]

The gas block must be installed over the little hole in the top of the barrel, so you can't just switch lengths of gas tubes at will.  If you want to install a mid-length forarm onto a carbine length barrel, you must replace the current gas block/A2 sight with very low profile model, or trime away the sight tower and bayonet lug from the one you have.  I would recommend replacing it with a low profile block since you can get one for $25 or so.
Then you can either replace the whole forearm with a free-float tube (I recommend the Hogue since it's easy to install correctly) or get a clamp-on style gas block to use as a "dummy".  Install it futher out toward the end of your carbine barrel to hold the forearm ring in place.  You will essentially end up with 2 gas blocks on the barrel, one that actually functions, and one that holds the 2 piece forearm in place (you'll have to purchase a mid-length forearm)
I would recommend the free float tube route it will be simpler than the 2 gas block route.  It looks pretty slick too since the gas block will be hidden under the forearm.
  Of course, you could always take the barrel to a gunsmith and have the gas port re-drilled in the mid-length position and have the carbine gas port plugged, but then you'll be purchasing a mid-length gas tube, a forearm, AND paying a gunsmith. 

[Lloyd Smale]

to do it my way youd have to buy a free floated handgurard and cut the top of your sight off leaving the gas block. Its easy enough to do and im my opinion makes a cool looking ar.

[Old Syko]

For an AR novice wanting to merely change from a car to a middy handguard the simple solution is to purchase a new upper and resell his present upper.  Otherwise the best way to learn is to take the present upper apart and see first hand how it is made.  The answers will then become apparent.  Erector set guns offer almost unlimited options of modification but you need to have replacement parts on hand or at least close by to make the changes possible.

[cjclemens]

Its really not that complicated.  You can do it two ways - Like Lloyd said, you can cut the front sight post off above the gas block.  Its not pretty, but its the easy way.  I wouldn't reccommend it myself, but there's no reason it wont work.  If you dont mind doing a little extra work, you can change the whole gas block to a low profile version. To do this, all you gotta do is take the flash hider/muzzle brake off, knock out the two pins that hold the front sight on and slide the front sight/gas block off the barrel.  Installing the new one is just the opposite.  Either way you do it, once you finish, all you'll need to do is slide the free float tube over the barrel and gas block and lock it into place.  Parts are available for carbine, mid and rifle length gas systems including gas tubes, barrels and handguards.  You shouldnt have to modify anything.

[SwampThing762]

Hey, guys.  Been away from the thread for a little while.   After having read all the knowledgeable responses from you kind gentlemen, I have decided that I will just keep the M&P-15 like it is, and just put together another rifle with a mid-length kit.    I am going to get a DPMS forged complete lower and install an M&A Parts Mid-Length Upper Kit on it.   Besides, it gives me an excuse to buy another gun and configure it to my desires.  Thanks, guys!

ST762

[cjclemens]

Thats what AR's are good for! if you want something different you can change it or order one the way you want it.