Putting together a M4 flat top upper for use on a M16, intrested in recommendations and advantages of the various high end free floating rail systems*, with primary concerns being stability and reliability.

• In particular any advantage of the RAS free floating system (looking at the medium if go with gas block only) over the RAS II (which does not require removing the front sight block,  but may not work with many / all sightless gas blocks)?

Second part of the question, for a folding front sight what options are there and which is recommended (while like fix front sights, have found the front sight base causes a blank spot with the night vision ... ).

1. Mounted on barrel folding sight - only option for a lug, requires either a new barrel or one with a full hole pin (have been told that issues if the current holes in the M4 barrel are half circles).
   



2. Clamp on folding sight, mounted to a gas block made for a front sight.  Only gas blocks with a tiny rail I have seen were with allen screws.



3. Clamp on front sight, mounted on a longer rail system (i.e. medium or extended RAS ... or similar products).  Using a "no sight" gas rail (only one have seen is the KAC which appears to use allen screws).

Thank You
John

* Not limited to KAC product line, just that my only experence with mounted high end rail systems has been wth the KAC product line (did find a dealer at the show with one ARMs rail system, however, hard to tell much as was not mounted]

Still prefer the Aimpoint M2 over the Eotech (at least this year ... ).

The night vision is old and a friends, which we still need to try with an ACOG (which is another thread).  Thus long term the night vission is TBD as will be replaced.

Thanks
John

The RAS II is the only FF RAS that does not require removeal of the front sight.

The PRI Front post is great but the one with the two allen screws requires removeall of a lot of barrel metal (making 2 somewhat shallow spots that I don't think are a great idea).  
[b]With PRI you get a beautiful sight picture by virtue of the rounded hood (reminiscent of a GLOBE front sight.) [/b]

The PRI front post with 4 set screws is a bette idea (but it is a bitch and a half to get it to sit level- took me about 30 minutes of ajusting screws.) It's amazing these people doesn't think about that and simply add a set screw to the bottom or something to keep it steady while it is being installed. Mine was not a tight fit (not a problem as those set screws pull the sight down into the barrel but I think a tight .75ID would help ease install also.) That may have been partially caused by the fact that I put it on a Dissy. [b]Now that it is in place I think it is a pretty good sight[/b]

The KAC FF RAS mounted sight is probably a nice sight deffinitely easy to install and eases replacement of the gas tube on FF RAS guns (a simple  twist of the collar and removeal of the FF RAS and you have full access to the gas tube) whereas on my rifle I would have to remove the FH and PRI front post to get to the gas tube (or drill holes in the FF RAS to access allen screws and do an internal install).
That's about all the good things I can say for it though [b] I guess to KAC low profile was #1 priority as the sight doesn't even fully shield the round disk of the front post base.  That looks tacky to me.[/b]

I would stay away from GG&G- just personal prefference there though.

Thanks for the information.  Trying to read between the lines, would a different rail system possible be recommended if one was using an ACOG or possible an Eotech?

Was reading your thread on [url=http://www.ar15.com/forums/topic.html?b=3&f=12&t=173105]New Gear[/url] and looks like picking a rail system is going to be much more interesting ... Thanks again for the information.

The PRI sight looks interesting, any have a photo of it mounted? [img]http://mstn.biz/images/Sights/PRI-Front-sm.JPG[/img]


Regards
John

I do... So does WES though.

Mine is not up on the internet like his.

I wish I had better image posting my villagephotos account sucks. Pictures are totally hazy.

I could e-mail you one if you give me your address.

RAS II with PRI Flip.  Please excuse the M900 grip light being so ridiculously forward.

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=15633[/img]

Hey, what do you know, Wes built that upper!!!