I would like my upper that I am looking to purchase to have a free float rail that will cover the front sight post/block because I want to run flip up front and rear.    It appears there are lots of complete uppers for sale with no front sight (railed block) but they come with standard handguards which I would want to change out to a free float.   Here is my question.  If I perhaps will be adding a free float myself will most handguards cover that RAILED gas block or do I need the smaller standard gas block (rounder).   Like is a railed gas block bigger and chunkier?   Since I want to do the least amount of work in buying a complete upper knowing whether I have to change out the gas block too is valuable info for me.  In a perfect world I would just leave the railed block and cover it with the free float.

 

And for anyone looking here.. I will soon be posting a WTB complete upper pretty soon..

 

If you are going with a ff guard then go with a low profile gas block, or a cut down front sight base.  

 

I'm not a 100% sure but I dont think the railed block with have the clearance.  Plus there's just no need to have it.  

 

ETA:  Some manufacturers will switch out the parts for you before switching if you ask.  Stag comes to mind. 

Any handguard I know will require a low profile gas block.

If you want it to look like this when you are finished you will need a LOW PROFILE gas block (some call it a micro gas block)

this set up has a 10" free float hand guard with a Low profile gas block

 

 

If you want it to look like this then you will need a 7" free float rail (some list it as carbine length) and a Rail height  Railed Gas block (the one in the photo is a Low profile Railed gas block. it has since been replaced with the Rail height.

I want a 12" rail so it will completely cover the block. Okay so no railed block, got it. Stag only makes carbines. I want mid length.

Railed gas block (like in my M&P15 ORC) is going to be too big and chunky to fit under a FF rail. You'll have to replace it with a low profile gas block so the FF rail can cover it. One thing you have to consider now is how you're going to replace the gas block if you have a threaded barrel with a pinned/welded brake that will prevent you from sliding it off the barrel? If the barrel you get is not threaded, no problem. If you decide to do it afterwards, get an upper with a standard FSB then just cut it down yourself.

 

http://njgunforums.com/forum/index.php/topic/52111-free-float-rail-suggestions/?hl=%2Bfree+%2Bfloat