I am in the planning stages of a carbine buildup.  It will be an A3 flattop with M4 contour barrel and a CavArms C1 (A1 length) stock.  I am still torn between Bushmaster and Rock River Arms for the brand.  Anyway...I want a flip-up rear sight in conjunction with an Aimpoint Comp mounted in an ARMS throwlever ring.  I am debating between the Swan Sleeve with integrated flip up sight and the SIR system with the addition of a #40 flip up rear sight (all from ARMS).  What is the weight difference between a SIR (handguards and mounting rail complete) and the combination of a Swan Sleeve and standard handguards?  Any and all help and advice would be appreciated.

if ya know you're not going to mount any lights or vertical grips then skip the SIR. Also you don't need the #38 swan sleeve if you use the spacer with the 22m68 mount. Sounds like you're gonna have a sweet setup no matter what. Remember to post pics when your done! I want to see the result of this one.

I personally would get a RRA upper over the Bushmaster because you'll pay a lot less for a product equally as nice.

I'd also get a SIR system as well because you never know what you may want next.  The SWAN sleeve is nice but the SIR offers more in the long run if you decide to add a vert grip or light.  Plus they weigh next to nothing and cool the barrel so much better than "normal" handguards do.  The SIR looks a lot heavier than it really is.  I'd be willing to bet it weighs no more than a SWAN sleeve and handguards setup.  If it does weigh more it's probably only 2-3 ounces.

This isn't quite the answer to your question, but when did THAT ever stop anybody.  Order yourself an ACE Skeleton stock fitted lower and mount a 16" VMatch upper on top of it.  That is the slickest combination I have ever had assembled - bar none.

I put an EOTech 552 on mine (here come the controversies).  Yes, batteries go dead, light bulbs break and electronic stuff is falable.  But so is everything.  And I check, and recheck (and test - obviously), all my gear before I deploy with it, cary spares of everything, believe in God and defend the right Country.

So if it's "my turn," so be it.  I'd rather die for something than live for nothing.

I'm actually an iron sights kind of guy myself.  But they're not really bullet proof either.  And the EOTech make shooting as easy as thinking.  Nothing to line up or focus on, just spot the dot and squeeze.  Bingo!

Just a thought - but good luck!  

just went through this process.  I am a Bushmaster man so my opinion is jaded as far as brand goes.  this is what I just set up.  Bushmaster flattop upper, 16 inch full heavy barrel, (M4 cut in barrel is, for the most part, pointless for us civilians) GG&G A2 flip up front sight,  GG&G scout lenght rail, Aimpoint ML2 mounted to the scout rail with the $15 aimpoint mount.  everything co-witness perfect.  The $15 aimpoint mount holds the scope as good as anyother and is a LOT LESS money.  It isn't quick release and that would be a good option but not worth and extra $100.  Advanced Armament Corp. assocessory rail and foregrip.  I have a GG&G ass. rail and foregrip on my other carbine but the AAC was half the price.  I like the GG&G foregrip better. and of course a CQB solutions tac sling.

I agree INFANTRYMAN,Im a bushmaster guy myself,I like rock river the quality is excellent except for barrels,The bushy is mil spec 4150 stel MP inspected,under normal use the steel quality is not a factor but for a field rifle the better steel performs better under the strain of rapid fire and hard use,So if I could get a RRA cheap I would but id still have to put a bushmaster barel on it.As far as barrels I perfer the heavy,ive got one on my pre and postban,I dont care much for the M4 profile so my carbine with a mag in gives the same weight as a full size,roughly a pound more,besides the M4A1 just go a heavier profile barrel to make it more reliable so heat wont make the barrel fail the way the lighter one has,maybe when they start ataching the M203 a different way they will use the more reliable especially for full auto fire HBAR.

The only differences between the uppers you've mentioned are;
The RRA (Wilson) barrel is 4140 steel, non chrome lined, and the BM is 4150 steel with chrome lined chamber and bore. Also the BM upper receiver has a "teflon" coating on the inside.