Yes, I've read the other topics on the FF issue...while they did answer some questions, they usually veer off topic (this IS arfcom!) or degenerate into personal attacks. Let us concentrate on what is known. To simplify matters, I would like to know any experience you all might have on the following issues:

1)POINT OF IMPACT: In another post, someone claimed that putting pressure on non-ff handguards would cause a shift in impact of 6" at 100 yards...If true, would you call that significant?

2)COOLING: Do ventilated ff tubes cool better than the standard HG's? Do aluminum FF tubes act as a heat sink, or is that canceled out by the radiant heat of the barrel?

3)WEIGHT: I know that each system has a different weight, but we must also consider the weight of the standard HG parts...in this reguard, Do you think a weight increase of between 1/2 and 3/4 lb. would be justifiable?

4)STURDINESS: How much abuse can the typical FF tube take? How about simply dropping it: would that cause a breakage?

5)CLEANING: I have not heard this adressed. How does one clean the barrel exterior on a FF tube that is not removable?

This is not an academic excersize; I am building two uppers and I may or may not go the FF route; your opinions would be welcomed and valued, because I have never had a FF HG. One upper will be a 14.5' light weight barrel "assault weapon" with M68 Aimpoint, on which I might add a forward grip, and possibly a tac light in the future. The second will be a 20" heavy barrel "designated marksman" type rifle with a TA-31F ACOG, which will prbably also have a harris bipod.

Given the 5 factors listed above, and given the fact that I want the DMR to be a consitantly accurate weapon using multiple support holds, do you think going FF is mandatory?

The system I was looking at was the new Yankee Hill "Tube Forearm System", which gives the option of putting rails where they are needed and leaving them off where they are not; to me this just makes sence!

1) Point of impact changes are significant; I don't know if they're of that magnitude without great pressure, but if so, do consider that POI shifts don't only affect accuracy; they have a seriously negative effect on precision, too.

If you're shooting from a benchrest, you're going to be putting inconsistent pressure on those handguards; the varying POI is operationally synonymous with poor accuracy.

2) Standard HGs suck for heat dissipation; Colt double shielded guards double-so. Most railed FF tubes with holes have better heat dissipation on account of better ventilation. Conductive and radiant heat imparted to the guards themselves is perhaps dissipated quicker, due to the high surface area presented by free picatinny slots and assorted design intricacies.

The tradeoff to high heat dissipation from the barrel, though, is that you'll feel more heat under heavy firing, as the operator. As an aside, the solid FF tubes are pretty notorious for getting obnoxiously hot; they trap heat to the barrel/handguard gap, and conduct it to a surface you're holding directly.

3) I personally feel the increase in weight to be justifiable; if weight is an overbearing concern, and you still want the advantages of FF handguards, you can get carbon fiber tubes from Hiperform and K2 Sports. There're more options, too.

4) FF tubes are usually more durable than the high impact plastic that your stock guards are, in my assement. Your rifle's still gonna be operable without guards, in any case.

5) I have never had or felt the need to clean the exterior of my barrel. If using a ventilated guard, though, you should be able to get a can of brake cleaner in there.

The easiest way to get free floating is to use the SIR system.  Get the "Civilian" model, the same one the Army Rangers bought.  Installs with a penny as the only needed tool.  This will free float your barrel and provide more rails than you'll ever be able to use.

SIR system will handle a front pistol grip (either ARMS or several others) and with the flip rear sight will have a good back up for your M60 CCO.

On very nice thing about the C-model SIR is if you don't like it you can remove it in a matter of minutes.  You can also remove it for detail cleaning if necessary.

-- Chuck

1)POINT OF IMPACT: How about on a short carbine length HG with a pistol grip...can differing pressure on the foregrip throw the POI off a human sized target at 100m?

3)WEIGHT: I saw an ad for the Wilson Tactical carbine; it has a vented aluminum FF tube and a fluted, meium weight barrel. They list total weight as 6.5 lbs. Is that true? If so, it seems like the weight addition can't be that much, at least on a carbine...

Weight varies.  SIR is heaviest.  DD has an aluminum barrel nut and is lightest.  IMO you want the lightest thing that you can get away with that still does everything you need.  The units that have their own barrel nuts do act as heat sinks but the effect is minor.  They offer improved cooling due to greater airflow.  If you drop a rifle on an exposed rail it will be ruined at the particular slot that recieves the impact... aluminum is not very strong so cover your rails with something.  POI impact shift is real and will be greater on light weight barrels.  You have no problem getting in to clean the barrel with a rail system.  As for the Yankee Hill system I have no experience but judging by their other products I would pass and go with something a bit more proven and robust.

So if the DD free float tubes are aluminum, then the KAC tubes are steel?

No, both tubes are aluminum.  The barrel nut on the DD is aluminum while the barrel nut on the KAC is steel.

Devl, which Yankee Hill product are you down on? They make FF tubes for Bushmaster & DPMS, among others, and Ive never heard a word of complaint about them...they have steel barrel nuts, but otherwise are quoted as being very lite. I was primarily interested in them because the rails are detachable...no need to worry about dropping the gun and ruining a $350 handguard! That, and the fact that all the tubes with the rails machined in tend to look like cheese graters...though maybe this would be a plus in CQB!

I free floated with JP Enterprises aluminum tube.  Threads on and off. Replaced gas block with the Bushmaster YHM flip up front sight and 3 rail setup. In the JP FF I put a stud mount for a Harris bipod and a second one for a Giles sling mount.

How do you like your new FF tube, Tacshot? Got anything to add about my "5 points"? What about the barrel cleaning issue; that still bugs me...

1)POINT OF IMPACT: In another post, someone claimed that putting pressure on non-ff handguards would cause a shift in impact of 6" at 100 yards...If true, would you call that significant?

[b]Half that is deffinitely true and very signifigant (without FF guards you have to concentrate on not putting pressure on the HG's) [/b]

2)COOLING: Do ventilated ff tubes cool better than the standard HG's? Do aluminum FF tubes act as a heat sink, or is that canceled out by the radiant heat of the barrel?

[b]Yes, Yes, and your better off if it is a highly ventilated FF RAS[/b]

3)WEIGHT: I know that each system has a different weight, but we must also consider the weight of the standard HG parts...in this reguard, Do you think a weight increase of between 1/2 and 3/4 lb. would be justifiable?

[b]Deffinitely you add rails for attachment of flashlights, grips and IR lasers, and you get the benefit of FFing the barrel[/b]

4)STURDINESS: How much abuse can the typical FF tube take? How about simply dropping it: would that cause a breakage?

[b]Dropping it won't break it. I don't really drop my guns often nor does anyone I know so I don't know how many times you can drop them from say 6ft without breaking one (I don't want to drop my rifle hundreds of times to find out either)[/b]

5)CLEANING: I have not heard this adressed. How does one clean the barrel exterior on a FF tube that is not removable?

[b]This is a pain in the ass.  you can take your cleaning rod with a patch on it and run it down the RAS and spin it and it will coat the barrel with protecting oil.  or if you have a RAS mounted front sight and low pro gas block you can just loosen the collar and take the RAS off. clean it and then put it back on and tighten the collar.

downside to that is that you never have a better than hand tight RAS collar, which means there will be more flex in the RAS than neccassary.

If only they made a rifle length RAS II.  that would solve the problems.[/b]


One upper will be a 14.5' light weight barrel "assault weapon" with M68 Aimpoint,

[b]If you never intend to use anything but reflex sights the SIR is a good choice (esspecially the bi-level SIR) but if you even think for a minute you might switch to an ACOG you better get an RAS II or FF RAS MRE, the SIR changes mounting height of the ACOG and that is BS.  I really like the SIR but I like the ACOG better, get the MRE if you may want to mount a Bi-pod[/b]

on which I might add a forward grip, and possibly a tac light in the future. The second will be a 20" heavy barrel "designated marksman" type rifle with a TA-31F ACOG, which will prbably also have a harris bipod.

[b]This is pretty simple, KAC FF RAS rifle length, or PRI SPR RAS system.

The PRI system costs more.  FFing the barrel is more important when you plan to use a bi-pod - or your prone unsupported and bi-pod supported zeroes may very well be different

If you used a SIR, you would probably wind up wanting a cheekpiece and that may or may not be possible while still providing clearance for the charging handle.[/b]

GreenO  URXII [:D]

I don't want to derail StormSurge's post but can't help but ask Chuck where he got his info on SIRs being purchased by US Rangers?

I've posted on this topic before, but have yet to see proof of any kind (pics etc) that any US Military units (and NOT Bremer's security detail) are using the SIR.

Thanks.

Will

The SIR's shure don't need cheek pieces, they are a lot lower than the carry handle for mounting. In fact they automaticaly provide the riser that many need to get to raise the flat top so you don't have to get high rings. The SPR Spec ops sniper rifles have the ARMS rail and they have no problem mounting and taking out the Taliban.
The Sir's have more capabilities than any other free float, to include being cooler under sustained fire, electronic intergration of things to come, rails where you need them or removed if not needed. etc., etc., etc.
SIR's don't need panels to protect hands from sharp hot alum at the 6 o'clock postion.
Modular options beyond anything out there, and is about as easy to install as can be imagined.
Jack

You forgot to mention that SIR's are also quite a bit heavier then most the other popular rail systems.

Since it includes a riser built into them, it is naturally heavier, that's why it is also more rugged.
Good shootin, Jack

"GreenO URXII"

I would be the first to jump on that bandwagon if KAC ever brought them out, the wheels of productivity seem agonizingly slow.

I don't care if they get the contract or not I know the benefits and would gladly buy one just to have a FF RAS with removeable lower pannel.

"The SIR's shure don't need cheek pieces, they are a lot lower than the carry handle for mounting. "

3rdtk do you ever do anything but promote ARMS? You don't even know what I'm talking about, [b]ACOGS[/b] if you mount one to a SIR it will be 4/10's of an inch higher than nominal, and this will screw with your ability to quickly aquire the picture in the scope. every time you shoulder the rifle that trouble aquiring the ACOG will shave milleseconds off your overall productivity as a hunter, shooter, soldier etc. Unfortunately there is no way to add 4/10in to the stock without interfereing with the charging handle.  IF the ACOG is to be used the SIR should not be used.

I talked to ARMS about the possibility of making a mount to mount the ACOG NSN 4/10s of an insh lower (or at least as low as possible) and they said while it was possible they weren't interested.

[b]So I'm not interested in SIR's because to me the ACOG is far more effective in enhancing my target aquisition than the SIR is.[/b]

THANKS for the info everyone! I got quite a lot of the kind of feedback I was looking for, so you are now free to veer off topic and flame one another to your heart's content! In fact I started the ball rolling by calling the RAS II a cheese grater! At the risk of offending 3rdtk, I would never put an ARMS FF unit on one of my AR's...If someone offered one to me, I'd say...NO SIR! Just prejudiced I fear; I don't like the way they look is all...

The problem with the SIR as GreenO has stated is optic mount height.  The iron sight height on an AR were not just randomly assigned.  They are the perfect level for the majority of shooters.

After a long time shoting a TA11 mounted in an ARMS 19S I can tell the extra .100-.125" it mounts above ideal.  This translates to a lack of 100% repeatability in cheek weld.  In turn I must raise my cheek above the line of sight where I can have a fully anchored cheek weld.  For this reason I am probably going to go to a TA31 which mounts at the propper height in a 19S direct to flat top.

The slightest head movement at long range introduces paralax error.  This is the largest negative with mounting optics too high.  Your shots can be moved inches off target with only a minute head repositioning.  

The SIR puts the optics WAY WAY out of line and you cannot use any cheek weld at all, this is much like a carry handle mount.  While hitting center mass at 100-200m may not be an issue a 300 yard head shot becomes more difficult to achieve.  I am not saying it cant be done but I must keep track of one more thing while shooting instead of just locking my cheek down and looking through the scope.

Contrary to what 3rdtk says all SPR rifles DO NOT use the ARMS rail.  Only the 1st generation units using the PRI foreend use the rail.  Current units built use the KAC forearm and ARMS QD scope mount direct on the flat top (which is lower).  Even then the medium (not high as stated by 3rdtk) rings are STILL too high.  You really need low rings to get the propper cheek weld on a current issue Crane built SPR.

Also I have never seen any evidence the SIR cools the "barrel" more than a FF RAS or other rail system.  If anyone has access to any documentation that shows otherwise please let me know.  I understand the forearm is larger and is further from the barrel and thus will have lower temperatures on the hand but that is not an issue for me as I neither dump multiple mags full auto at enemies and I use a vertical foregrip which is more effective for a M4.

Greeno
When I see hog wash I will point it out, via facts! The AGOG's were designed and issued to troops after many test and evaluations by the military, to be used in the carry handle, by the many thousands. The carry handle puts the ACOG aprox 1/2" higher than on a SIR or any of the other risers. Not opinion just a fact.
Jack