I'm building a pseudo-SPR rifle w/18" WOA midlength barrel.  I want to ditch my front sight base and put on a gas block and folding front sight, but here's where things get strange.  I thought about using a midlength varmint style free float tube, or perhaps a customizeable tube where you can add the rails where you want them.  To do that I would need a railed gas block so I could install a flip up front sight.  Then I got to thinking, why don't I use a low-profile gas block and install a rifle length rail system so I could mount my flip up to the top rail, and bipod to the bottom rail?  Which would you do and why?  Midlength rail/tube with railed gas block or low profile gas block w/rifle length rail?  Keep in mind, I will be installing the new YHM Stainless Phantom supressor so I would need enough room up front to mount that.  MJD

While rail mounted front sights are technically not as precise since they are not attached to the barrel, I prefer them because they dont get hot, dont weigh much, and can be changed out.  Keep in mind it is a BACK UP sight and not a primary sight.  You wont be using it much so I would go with what will be the easiest to install, use, the least expensive, etc.

I went with a 12" rail on my midlength RECCE.  I'm using a set of Troy flip ups for my BUIS.  The longer rail works well for me.  The gas system is completely covered (protected) and I have a longer sight radius.  

Not that I run it hard enough to need a protected gas block or fall back to irons but that's how I justified the longer / more expensive rail.