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CHIGGA73
09-27-2009, 8:56 PM
Ok guys, I need some help

i have a Knights Armament Co. 2 piece Quad rail, Carbine Length.
From what i have gathered from research and the rail numbers, it is a Knights M4 RAS (KAC p/n: 98064)

I have a DPMS M4 upper that I want to put it on, and it will not go on.

The front of the top rail portion has a part that sticks down and does not fit over the Barrel contour on the rifle. It is the part i'm pointing to with the pencil in the picture below.
http://i394.photobucket.com/albums/pp23/CHIGGA73/100_9094.jpg

Do i need a different barrel contour? is there any other option? It is a standard barrel contour from a prebuilt upper i got and it hits on the barrel at this point (see pic below)
http://i394.photobucket.com/albums/pp23/CHIGGA73/100_9096.jpg
I'm not even sure if it will work as the rear doesn't fit between the barrel nut and handguard slip ring, even if it fit over the barrel.

let me know what you guys think or can suggest.
thanks for the help in advance.

dieselpower
09-27-2009, 9:32 PM
FYI...you have a new style M4 heavy profile barrel....
....The RIS and RAS units are similar in that they consist of two major components: a top component consisting of top, left, and right quadrants, and a bottom component consisting of a bottom quadrant. Each quadrant contains a MIL-STD-1913 rail that can be used to attach a variety of weapon accessories. Differences between these two units occur in the way that they attach to the handguard cap and delta ring/barrel nut, how the units are numbered, and the types of barrels that they can be used with.


Rail Interface System (RIS) (KAC P/N: 94297)

The RIS is the older version of the two systems and is numbered T-L-R-B (top- left-right-bottom) in odd numbers 1 - 13 beginning at the front sight and ending at the upper receiver. The RIS system works with a wide variety of barrel contours and mounts like a conventional handguard except for an adjustable metal tab, at the handguard cap, that squeezes the two halves together. At the rear, the RIS unit is held in place by the delta ring.

The biggest advantage with the RIS system is that it is able to accommodate a wide variety of barrel profiles while the disadvantage is that the RIS doesn’t clamp to the weapon as solidly as the RAS system. Just the same, the Navy SEALS reportedly prefer the RIS over the RAS system for the advantages described above........
Sorry it took me so long to find this couldnt remeber were I read it.

and

In the last few years, M4A1 carbines have been refit or received straight from factory with barrels with a thicker profile under the handguard. This is for a variety of reasons such as heat dissipation, which is useful due to the complaints of high-heat production from test soldiers, which occurs during full-auto and accuracy as a byproduct of barrel weight. These heavier barrel weapons are also fitted with a heavier buffer known as the H2. Out of three sliding weights inside the buffer, the H2 possesses two tungsten weights and one steel weight, versus the standard H buffer, which uses one tungsten weight and two steel weights. These weapons, known by Colt as the Model 921HB (for Heavy Barrel), have also been designated M4A1, and as far as the government is concerned the M4A1 represents both the 921 and 921HB.

so you have a new M4 barrel where the RAS will not fit on...you need a FF KAC or RIS

CHIGGA73
09-27-2009, 9:37 PM
according to the numbers it is a RAS with the even numbers 14-28 (top, bottom, right and left). That is why i think it is the RAS not the RIS system. I'm assuming in need the RIS system to fit my current AR upper barrel contour but i didn't buy this and want to see what i need to do to get it to work.

Pryde
09-27-2009, 9:40 PM
In the last few years, M4A1 carbines have been refit or received straight from factory with barrels with a thicker profile under the handguard. This is for a variety of reasons such as heat dissipation, which is useful due to the complaints of high-heat production from test soldiers, which occurs during full-auto and accuracy as a byproduct of barrel weight. These heavier barrel weapons are also fitted with a heavier buffer known as the H2. Out of three sliding weights inside the buffer, the H2 possesses two tungsten weights and one steel weight, versus the standard H buffer, which uses one tungsten weight and two steel weights. These weapons, known by Colt as the Model 921HB (for Heavy Barrel), have also been designated M4A1, and as far as the government is concerned the M4A1 represents both the 921 and 921HB.


Dude,
You are wrong on this one. I have a Colt 6921HB upper with the thick profile under the handguards and the RAS its been wearing for the past 2 years fits over it perfectly. I think its the out-of-spec DPMS barrel which is giving you fitment issues.

To the op: you are gonna have to dremel the RAS to make it fit, or ideally get a better barrel than DPMS.

dieselpower
09-27-2009, 9:56 PM
How far out are we talking...like 1 mm or a lot like a 1/2"? By the pics it looks like its very far out which leads me to believe this is a barrel profile problem.

If its minor mis-fit, then I will go with DPMS goof as well.

I dont know what it looks like, since I didnt notice it. I can't remember if it was that fat at the front or not.

maybe AR15barrels can provide some light...
http://www.ar15barrels.com/prod/govt.shtml

EDIT>>>>>>>>>>>>after looking at that page, I am wrong. The taper is old and you have a taper so....DPMS screwed the pooch.

or the rail is a airsoft clone.

CHIGGA73
09-27-2009, 10:29 PM
i'd rather no dremel it off, because it seems the rear doesn't even fit between the barrel nut and the handguard slip ring! i don't want to cut up both parts.

I don't think it is a airsoft clone as it is stamped and has all the right markings i believe and i got it from a friend that was in the military.

I'll try to see if it fits on someone else's upper, or see what other barrel options and barrel nut options there are to make sure it fits. It is a nice piece and i don't want it to go to waste.

818gtiguy
09-27-2009, 11:00 PM
I have the solution..Sell the KAC rail to a buddy or here in the Calguns classified, then buy a Daniel Defense Omega Rail..Drop in with no modofications..Free float and solid as a rock..

CHIGGA73
09-28-2009, 1:44 AM
nice, are you offering to be a "buddy" haha!
i thought about selling it, but i'd rather not go through the hassle finding out something that is similar in value...or buying new...etc. y'know. i wanna try to see if there are other options before i do that!

Timberland
09-28-2009, 8:47 AM
Do you own a dremil? If so problem solved.

CHIGGA73
09-28-2009, 12:06 PM
i do own a dremel, but i was hoping that it wouldn't have to come to that!

any other ideas guys?

aplinker
09-28-2009, 5:55 PM
I only have a RAS for a rifle, but it looks like you have it backwards, if you're trying to put the parts where you're pointing the pencils at to be the same.

The metal part at the top likes like it is what tightens to the delta ring/barrel nut assembly.

CHIGGA73
09-28-2009, 6:30 PM
the point i'm pointing to on the quad rail is the front according to the numbers and the direction arrows inside.

the back has a allen screw and a thing that is loose and drops down to tighten as you were saying. I'm pretty sure i have it facing the right way. I tried it the other way and not even close. the pencil is pointing to a fixed part that hits the barrel (at the pencil pointing part on the rifle) and won't allow it to fit.

i'm stumped.

dieselpower
09-28-2009, 8:37 PM
two things.
1) Airsoft parts have the EXACT same markings as the real thing, but they can not fit on a real firearm. The China clones look nearly identical to the real thing and will fit a real weapon. A buddy of mine bought a Magpul on e-bay and it was a airsoft copy authorized by Magpul, but would not fit on a tube without cutting it up.

2) I see you said you got it from a buddy who was in the military...you only meant he would know what was real, since you also know it's against the law to sell or give away military gear and the military has the right to TAKE the property back no matter where it is stored.....

CHIGGA73
09-28-2009, 9:51 PM
yes, he worked on guns himself and was in the military. This was his personal stuff.

I do not know 100% if it is Airsoft clone parts. the markings are inside and outside and appear to be correct. I don't have another one to compare it side by side though.

thanks for the points to look at. i'm just hoping to get it to work and seeing if anyone else has had this kind of issue.

Cyclepath
09-28-2009, 11:15 PM
I have 2 of the KAC RAS and had to modify them both. Yes, you will either need take a dremel or use a round file and shave off a little material at a time where the metal piece contacts the barrel. Just go slow and take off a little at a time until it goes on snug. The only issue is that after that, the rails may not be snug if you decide to switch to another upper if the barrel profile is slight smaller.

The piece can be removed by punching the roll pin out. Maybe KAC might sell the part if you need another one?

Pryde
09-29-2009, 12:50 AM
An airsoft RAS will not have a knights logo stamped into the heatshield and it will have an incorrect phone number etched on the side. I am pretty sure based on the OPs post that it is a real RAS. The problem is that the RAS is designed to fit a milspec profile barrel. A lot of aftermarket manufacturers of dubious quality such as DPMS or Olympic have barrels that are not contoured to spec and will not mate with the RAS.

paladin4415
09-29-2009, 9:08 AM
From the one picture and your desription of the source, I'm pretty sure you have a genuine KAC RAS. The problem is that DPMS and several other commercial grade AR makers don't profile their barrels the same as the mil-spec makers do. The KAC RAS is designed for a mil-spec profiled barrel. The only way to get it to fit that upper is going to be to remove a small amount of material from the front lug on the upper rail. If you do this, remove a very small amount at a time and keep test fitting to the upper until you remove just enough to allow it to go forward under the cap.
With regards to the problem you see at the rear (delta ring) area. If you choose to remove some metal for the lug it should fit fine. Make sure you have removed the set screw and that the locking lever moves easily and is in the down position when you install the upper rail. Also make sure that the spring tab on the front of the rail (shiney part) is UNDER the cap and that rail is all the way forward when you drop the rear in. Make sure that the locking lever does not get caught on the gas tube as you lower the rear of the rail.
Make sure you want to do this before you start removing metal from the rail. Once you fit it, it's married to that upper.

paladin4415
09-29-2009, 9:13 AM
i saw one lt. walk by, his mag fell out, and his rail fell off too. and guess what? it was a kac. ive seen mags fall out before, but thats the only quad rail ive seen fall off.

If that rail was properly installed. It is not physically possible for it to "fall off" unless it was severely damaged.

CHIGGA73
09-29-2009, 2:53 PM
thanks cyclepath, that's what i needed to know. hearing someone else had to fit it also lets me know it may be ok to cut.

paladin, thanks for the heads up. i think i am going to try to slowly make it fit. I don't plan to get rid of the upper anytime soon nor do i plan to buy another "mil-spec" upper hoping it is the right barrel contour.

Jicko
09-29-2009, 3:03 PM
Bro, why don't you contact KAC?

shark92651
09-29-2009, 3:45 PM
Bro, why don't you contact KAC?

Yeah, just don't tell them you are in California or they will probably refuse to talk to you and demand you send the parts back to them :rolleyes: