Knight Armament UK-SAS Lower Rail w/Clamp does turn the R.A.S. into a FF Rail or not? I have seen this on Operation Parts.com . I know this might be a Dumb question.

Quoted: Knight Armament UK-SAS Lower Rail w/Clamp does turn the R.A.S. into a FF Rail or not? I have seen this on Operation Parts.com . I know this might be a Dumb question.

No such thing as a dumb question...

The SAS lower does not make the RAS into a FF rail.  The bottom rail that comes stock with the RAS does not have a locking clamp so there is a possibility that it can pop off at the most inopportune time.  The SAS lower corrects this, but at a price.

IMHO, for that much $$$ you're better off getting a FF rail.

Quoted: The bottom rail that comes stock with the RAS does not have a locking clamp so there is a possibility that it can pop off at the most inopportune time.  The SAS lower corrects this, but at a price. IMHO, for that much $$$ you're better off getting a FF rail.

I think the UK-SAS rail is more for stabilizing the bottom rail than for keeping it from popping-off (which this would stop that as well). If your RAS lower popped off then you have delta ring problems.

Quoted: I think the UK-SAS rail is more for stabilizing the bottom rail than for keeping it from popping-off (which this would stop that as well). If your RAS lower popped off then you have delta ring problems.

Though it has not happened to me, I can see how a RAS lower could come lose if using a VFG - and the delta ring is fine.

Here's a recent quote from someone that is in the know:

WHY ONE CUSTOMER IN THE SANDBOX ORDERED THE UK/SAS LOWER FOR HIS M4 RAS:

"That SAS Lower part would really have come in handy a few days ago!. It is kinda embarassing to have your lower handguard pop off when you barrel thump someone!"

WES GRANT
M.S.T.N.

Although pricey, I am planning on getting one for my RAS.  I don't like that loose shifting feeling of the lower rail when holding the vertical forward grip.  I have a RAS II equipped upper that has a similar SAS style lower rail and feels extremely solid compared to the RAS.

Quoted: Although pricey, I am planning on getting one for my RAS.  I don't like that loose shifting feeling of the lower rail when holding the vertical forward grip.  I have a RAS II equipped upper that has a similar SAS style lower rail and feels extremely solid compared to the RAS.

Glad you posted that.  I was thinking about getting one for my RIS, and I've got an RASII on order.  It sounded like the lower rail was similar to the SAS unit, and I was wondering if I needed to go ahead and order another one.  Sounds like I don't.

OK, no dumb questions, right?


Has anyone successfully modified an existing RAS lower rail to accept a barrel clamp?
There are way too many crafty folks here to not try it!

I figure a cross pin and a machined/fabbed/tapped clamp might work?
I don't believe the rail would be rendered unusable if the project didn't work...

maybe just a bit of heatshield/rail material gone?


dammit I need a mill!!

Quoted: Quoted: Although pricey, I am planning on getting one for my RAS.  I don't like that loose shifting feeling of the lower rail when holding the vertical forward grip.  I have a RAS II equipped upper that has a similar SAS style lower rail and feels extremely solid compared to the RAS. Glad you posted that.  I was thinking about getting one for my RIS, and I've got an RASII on order.  It sounded like the lower rail was similar to the SAS unit, and I was wondering if I needed to go ahead and order another one.  Sounds like I don't.

I was thinking about selling a RAS to get another RASII.  The RASII is best used for an Aimpoint or an ACOG.  The RAS/RIS would be perfect if they came equipped with the UK-SAS lower rail.  I'm still going to get one.

Quoted: Quoted: Quoted: Although pricey, I am planning on getting one for my RAS.  I don't like that loose shifting feeling of the lower rail when holding the vertical forward grip.  I have a RAS II equipped upper that has a similar SAS style lower rail and feels extremely solid compared to the RAS. Glad you posted that.  I was thinking about getting one for my RIS, and I've got an RASII on order.  It sounded like the lower rail was similar to the SAS unit, and I was wondering if I needed to go ahead and order another one.  Sounds like I don't. I was thinking about selling a RAS to get another RASII.  The RASII is best used for an Aimpoint or an ACOG.  The RAS/RIS would be perfect if they came equipped with the UK-SAS lower rail.  I'm still going to get one.

And I might be selling my RIS to finance a new mount for my M68.  The Railgrabber is too long to fit the hump, and I don't know that I like it jumbled up on the front 40.  BTW, got the RASII today.  So far, it looks to be great.

Is the lower rail of a RAS II the same as the UK-SAS lower rail, or is the UK-SAS lower rail also an upgrade for a RAS II as well as a RAS or RIS?

I assume that when it is stated that the UK-SAS lower rail clamps onto the bbl nut, it means with the use of an allen screw in addition to the use of the delta ring like a RAS II.  Is this correct?

Quoted: Is the lower rail of a RAS II the same as the UK-SAS lower rail, or is the UK-SAS lower rail also an upgrade for a RAS II as well as a RAS or RIS? I assume that when it is stated that the UK-SAS lower rail clamps onto the bbl nut, it means with the use of an allen screw in addition to the use of the delta ring like a RAS II.  Is this correct?

The RASII lower is not compatable with the RAS upper.
- The RASII lower has 'ears' on it that lock in place in the RASII upper but will not fit on a RAS upper
The UK/SAS lower is an upgrade for the RAS (it may work on the RIS but I dont know for sure)

Functionally both lowers (RASII and UK/SAS) work the same but the RASII has ears that prevent it from fitting on a RAS (I guess for some extra support since if a FF unit)

I bought a RASII thinking I might be able to use the RASII lower on a RAS....no such luck. So I bought a UK/SAS lower in the true ARFCOM spirt and kept both

The RASII is set up a little differently than the RAS/RIS.  The upper guard of the RASII jams back against the delta ring.  It is held in place by the clamp that straddles the gas tube and goes under the barrel nut and the cross bar clamp on the upper receiver.  The front end is just short of the handguard cap.  It does not fit under the cap.  The lower part of the RASII has slots in the forward edge that engage tabs in the bottom of the upper guard that secure the forward end, while it has a clamp similar to the upper that wedges under the barrel nut securing the aft end.  The delta ring just fits over the aft end of the lower guard.  If you use a Masterkey or barrel-mounted 203 then the lower is irrelevant.  Either way, the delta ring is held under tension to the rear by the upper guard to the point that the "teeth" on the barrel nut are visible.  It's basically a free-floated unit
The RAS/RIS is held in place by the delta ring and handguard cap, something the RASII is not capable of doing.  
ETA:  since the SAS unit is meant to work with the RAS/RIS which require contact with thr handguard cap, I don't think there is any compatibility as ROMAD said.

Great info here.

I've got an old RAS, made in '99 and so far no play in the lower yet.

If it ever developes the play later, I'll check the delta ring assy and I might get the UK-SAS lower rail to fix the problem.