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Posted: 4/2/2012 12:09:25 PM EDT
Hello to everyone in this forum it was recommended to me to re-post theses questions here ( I had posted them in the A2 forum ) so here is the following posts that I had placed in the A2 forum :

[Does any body have a blueprint copy of the USAMU DCM/CMP legal freefloat tube ? or know where I could download it from. Also whose finished A2 upper do some of you guys like to start from with building a match gun ? any pref. I will be doing all of my own machining. Thank You, Doc.

Ok no response yet on the tube that is ok I just figured I would see if any of the members on here have machined there own before, I like the challenge. As far as the A2 upper is concerned I have found some useful content in the forums. Next question for all you NM, CMP, NRA shooters out there. After reading over the CMP rule book A4 uppers are now legal and they have also listed that you may use a quad rail fore end on the gun. It does not clearly state what type of quad rail just its diameter. So my tech question is can it be a free float or is a sopmod two piece type that use the delta ring, and is this legal only on the A4 upper or can I use this on a A2 upper. I really want to stick with the A2 upper for match for elevation purposes. Any and all help would be greatly appreciated I have not shot high power in years and things have changed some since my time. Thank You, Doc. ]

Any comments, recommendations will be greatly appreciated, Doc.
Link Posted: 4/2/2012 4:28:28 PM EDT
[#1]
I can only offer my opinion on why you are not getting any responses. Floating tubes (CMP legal) are readily available and are not too expensive. It's a waste of time to build one unless you prefer doing things the hard way.
Link Posted: 4/2/2012 5:51:59 PM EDT
[#2]
Found this in a post Grandpa made here a while back.
He was talking about the new CMP rules.
6.2.3.14:

The M16A4 quad rail or commercial equivalent hand-guard may be used.
The quad rail must be 12” in length and have four rails at the 12, 3, 6 and
9 o’clock positions running the entire length of the hand-guard. The diameter
of the rail must be at least 2” and not more than 2.5”. The front sling
swivel must be attached to the front end of the hand-guard. The standard
A-frame front sight must be fi xed in the as-issued position on the barrel.
Plastic covers may be used on the mounting rails on the hand-guard

So if it has to be 12" in length I assume it can be used on an A2 upper no? (standard A2 upper handguards are 12")

I would rather use the standard plastic handguards anyhow, they just seem to fit my non-firing hand better.
Link Posted: 4/3/2012 4:08:02 PM EDT
[#3]
I would like to thank everyone who has responded to my questions regarding the free float tube, and the A4 rail questions. I agree that from reading the rules it should not make any difference on a A2 or A4 upper. I would like to use a A4 upper for other purposes than NM, but I do not like the elevation limits of the detachable carry handle. I have read very limited info about individuals using NM sights in the carry handle and counter boring the upper receiver to take in the longer elevation stem. Has any one here done this ? If so does anyone have pics or know where there are pics posted ? If this is done do you change out the front sight base for height purposes, I would think you would want to ? Looking forward to comments and info, and thanks again. Doc
Link Posted: 4/3/2012 4:22:08 PM EDT
[#4]
I think RRA or WOA makes A4 handle with the same elevation max height as A2 or at least higher then in other brands. I am not 100% sure, some one here should know.
Link Posted: 4/21/2012 7:35:35 PM EDT
[#5]
This is a USAMU free-float tube with lightening holes.  The AMU makes their own tubes as opposed to buying commercial.



Rock River makes a National Match carrying handle for A4s that has a higher rear sight shelf to get the full range of elevation to 600 yards.

If I planned to use a free-float rail I'd use a Larue or Daniel Defense.

This is one built from a free-float tube and a Knights GI M5:

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