Hi Y'all,

I noticed a post awhile ago that stirred up a lot of controversy about the various premium handguard/rail systems available. I may have the same basic question as the original poster, but I'm really just trying to figure it all out.

SO:
What exactly are the benefits of the KAC/RAS/FIRSH etc systems?
Do they make dissasembly and maintenance difficult?
I'm getting ready to build my own AR. If the only thing I expect to mount is a flashlight, do I need one of these systems?
Do they add weight compared to standard handguards?

Thanks!

I don't know or own ARMS SIR so can't make comment on it.  
Better heat disipation, rail surfaces for mounting sights, lights and forward grips.  On RASII and FF models the barrel is free floating, the devices mounted on them won't affect the accuracy and they offer even better cooling.
coldblue and 3rdtk will be able to give much better explanations [:)]

I am in a similar boat in that I am building my own AR as well.

I would say that the benefits for a non standard hand guard are free floating and having a way to attach accessories.

However, they will make assembly more complex depending on how much you are actually building an upper.

If you are building an upper from scratch, then it is not any more complex.  If you get a FIRSH or another free float (non SIR/RAS II) and are building from scratch, just get a barrel with no muzzle brake and DO NOT get the delta ring assembly.

Also if you get a SIR or RAS II, then it is just about as simple and conventional handguards.

Personally, I just want to be able to Free float the barrel, but on a bipod and maybe a light.  It should be relatively simple since I am going to build the upper from parts and the barrel I am going to get will have a plain end.  So I am going to put on an aluminum FF tube (less that $60) and then bolt on a short weaver rail and a sling stud (for the bipod). On the other hand, I might get the mid length FIRSH since I want to build a midlength upper.  Either way it will free float. It is what I want and all I need for my purposes.  If I used this for a job, I would probably get the SIR or RAS II, but then the job would hopefully pay for it.

Hope that helps.

If all that you plan to do is mount a flashlight and you intend to leave it on, then no you probably don't need andthing other than standard HG and a light mount.

Heat dissapation is often mentioned but i don't seem to recall any GIs standard handguards bursting into flames after several mags at full auto.  Even if it does make a difference i can't imagine a civilian using a semi AR putting enough volume through it to make a difference unless he's just dumping ammo.  

Some designs do make it harder to clean than standard HGs, in some cases requiring tools.  I haven't found this to be a problem with the CMORE quad rail on one of mine but maybe i just don't get it dirty enough.

Yep they add some weight, on the order of a few ounces.

Many of the HG systems people are going to are free float which some claim helps accuracy.  For a weapon it won't make a bit of difference for the range it may ( i can't tell the difference).  One good thing is that anything you mount to a FF HG shouldn't affect your zero if you remove it so if you plan on popping your light on and off you may want to consider a FF.

The biggest advantage to a good, solid HG system is that you can mount sighting devices such as lasers or reddots up front without worrying about the zero shifting.  I don't plan on ever using a laser and i like my reddot mounted a little further back so this also is not an issue IMO.

The biggest disadvantage is the cost.  If your budget is such that it will come out of your ammo kitty, don't spend the bucks on a fancy HG.

Myself i have a RAS II on order going on the new flattop i'm building.  For the cost of it and my buttstock i could build another complete rifle but i'm a gear whore so that's what i do.

Selecting a rail system depends on many factors.  You should keep in mind the purpose of the rifle, the optics you will be using and the other accessories you will be mounting such a lights, lasers, etc.  Last but not least, personal preference will play a big part, always get the system that works best for you!

As I mentioned on my project post,[url=http://www.ar15.com/forums/topic.html?b=3&f=12&t=162739]M4 Project Notes[/url], I originally planned on getting a Knight's M4 RAS(Rail Adapter System) but as I did some more looking around I found that there were other rail systems that had better features while not costing much more.

Some of the problems that faced the RAS system were the inability to securely mount optics, the heat shields protected your hands but actually kept the heat in the hand guards rather than dissipating it, the RAS did not free float the barrel causing some issues as more accessories were mounted.

I decided on the arms SIR 50 system because of the following advantages it offered.

1. Completely rigid full length rail for installing optics, lasers, etc.
2. Completely free floats the barrel.
3. Excellent cooling, bested only by older larger model SIR 45.
4. Rails of different sizes can be added or removed as needed in the 3, 6 and 9'clock positions.
5. Bottom half of hand guard is polymer and can be removed to access the barrel for cleaning.
6. Bi-level feature allows for co-witnessed forward mounting of EOTech optics.
7. Integrates perfectly with the ARMS 40 BUIS.
8. Easy to install requires no special tools or rifle disassembly other than removing the hand guards.

The other deciding factor was price.  The Knight's M4 RAS was selling at $285-$300 and I was able to find a dealer selling the SIR 50 for $355.  I felt the small extra amount was well worth all the advantages.

Note the older SIR models, the 45c(Commercial/Civilian) and 45m(Military) were a bit bulkier and the 45m required removal of the delta ring for installation.  Ironically the preference of the military was the C models which allowed you leave the delta ring and easily switch another configuration if needed.

Knight's has a Free Float RAS which is very nice system but it requires removal of the front sight and replacing the barrel nut for installation.  Other the more difficult installation I felt it would also take away from the versatility to switch to another system if needed.

Knight's also has a newer rail system the RASII which has many of the features of the SIR 50.  It's a bit less around $330 and is also a very good system.  I still felt the SIR was an overall better system especially for my needs, still the RASII would be my very close second choice.

So far I'm very happy with the SIR 50!  It has perfromed as advertised and the way it mounts makes it feel totally part of of the upper receiver.  If I do my part my carbine can easily do 3/4 MOA and the SIR keeps everything nice and cool during extensive rapid fire sessions.

Here's some some pics of the RAS, FFRAS and RASII.
M4 RAS
[img]http://quarterbore.com/images/kacm4ras.jpg[/img]

FF RAS
[img]http://quarterbore.com/images/kac_ff_ras_family.jpg[/img]

RASII
[img]http://quarterbore.com/images/kacrasiij.jpg[/img]

Here's some of the other SIR systems.
[img]http://www.armsmounts.com/images/sirs.jpg[/img]