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Posted: 5/29/2002 3:52:23 AM EDT
Hi all,

I've got a DPMS CAR15 (Export version 16" heavy barrel, Bayo-lug and flashhider).

Now I can buy a Knights RIS system form somebody. My question is. will it fit the heavy barrel of my carbine.

Other question,  has anybody tried the OA FIRSH
setup. It's about $ 200,- cheaper than a RIS/RAS. or is it "get what you pay for".

Just curious.

Link Posted: 5/29/2002 6:25:55 AM EDT
Link Posted: 5/29/2002 11:49:04 AM EDT
Just to clear some things up...a RAS will fit over a heavy barrel.  I have one mounted on one of my rifles right now.  This applies to Bushmaster Heavy barrels.  If your inquiry pertains to bull barrels, then it obviously wont fit.

See attached pics:

M4 Standard Carbine barrel

16 inch Heavy barrel

Now take a look at the width of the barrel right before the front sight post where the RAS would connect when attaching the forward portion to the front handguard retainer.  Its the same...or very close to being the same.  My RAS fits over the heavy barrel perfectly flush.  This includes the metal tab that captures the top of the forend cap up front.  Nothing was forced during installation.  

Now take a look at the barrel nut.  Although you may see a slight difference in the circumference of the barrel...it doesnt matter because the locking bar on the RAS will fit under the barrel nut on a Bushmaster heavy barrel.

Link Posted: 5/29/2002 12:17:09 PM EDT
One more comment,

    If your gas tube is not perfectly aligned from your gas block...back to the upper reciever, you may have problems lining things up due to the fact that the locking bar on a RAS straddles the gas tube by the barrel nut.

    Another observation in reguards to the NATO STANDAG rails on the RAS and the upper reciever.  Mine are perfectly in line.  I'm not sure if it is because of the heavy barrel, but when I had the RAS mounted on a standard M4 Carbine barrel it was off by just a hair.

    The way I tested it was to place my aimpoint on my upper reciever and look through my iron sights.  The red dot was in perfect alingnment with the front sight post (both vertically and horizontally).  Then I mounted the aimpoint on the RAS and looked through again...the dot was in the same spot, perfectly aligned with the front sight post (vertically and horizontally).

    When the RAS was on the stanard M4 barrel, the dot would be off a hair (horizontally) when the aimpoint was mounted on it (as compared to the upper reciever).

    Since it has been stated from other posts that the RAS will fit "pencil" and "standard" barrels...this implies a "range" of circumferences that the RAS will accept.  This specifically pertains to the front portion of the RAS where it mates to the barrel.  I submit that the Heavy barrels (Bushmaster) are at the upper limit.  Since it mates perfectly to the heavy barrel, it may account for the rails lining up perfectly with my upper reciever.

...but then again, it could be because I built this rifle myself and the barrel/barrel nut was indexed and torqued correctly.
Link Posted: 5/29/2002 1:55:24 PM EDT
Link Posted: 5/29/2002 2:48:40 PM EDT
There you have it...


    Are you going to be at the Houston show this weekend?
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