I have a Bushmaster Dissipater 16" barrel.  It is my patrol rifle.  No complaints about the accuracy.  This rifle is an honest to goodness 1" gun at 100 yds with iron sights - if I do my parthaving
Any experience out there as to whether free floating helps the accuracy on a HB AR?

Also, since I'm asking, is there any info on the velocities of differing loads for the 16" vs the 20" barrels?  Our department is using Black Hills 60gr SP.  I only know of one shooting so far, almost point blank range, went through the guy's arm and transversed his chest.  VERY effective, but, like I said, point blank range (maybe 5 yds?).  

Thanks for your help.

IF your rifle is shooting 1moa, leave it alone IMHO.  I would, however, wonder if your rifle is still MOA when shooting from sling supported positions--where pressure from the sling might bring the handguards into contact with the barrel.

Anyway, if this is your patrol rifle, you don't need varmint/benchrest accuracy nor the ability to fire dozens of rounds before heating up.  What you likely need is a fast moving, light to carry rifle capable of putting rounds quickly on target.  Going to 20inches is going to dramatically increase the weight of the rifle and slow your implementation of it as well.  You will gain a bit of velocity, but even with a 16 inch barrel you should still be in fragmentation range out to 100 yards or so.  Do you anticipate taking shots beyond that range???  Does your department even allow shots beyond that range??  If anything, I'd suggest sending your barrel to adco and getting it turned down a little to shave some weight and you'll have a well balanced, light rifle that can put rounds on target with acceptable terminal balistics out to at least 100 yards and likely out to 150 or so.

I was not thinking along the lines of patrol rifle.  I retire in a couple of years TLW, and wanted to have a worst case scenario weapon that could occupy two roles - CQC assault weapon as well as a sniper rifle.  Plus, I don't think that just 4" is going to add that much weight.  The 16" barrel is an HB already.

However, I'd really welcome any help on the effectiveness of a free float tube.

The free float really comes into play only when shooting when there can be stress on the barrel.  Most NM guns are floated because in NM shooting the shooter is slung up VERY tight, which will put stress on the barrel.  Other instances are extended firing supported on a bipod, or just plain precision shooting supported on a bipod (or anything else that will put pressure on the barrel).  Precision folks like to eliminate variables, and any stress on the barrel can shift point of impact, which they don't like.

If 1" is good and you aren't chasing tiny groups or precision shooting, you should be fine without it.
Personally I like free-floated, because I do shoot off a bipod and when I use a sling its not just for carrying the weapon.  Also with a railed free float tube you can mount optics to it and not worry about them moving.

Quoted: wanted to have a worst case scenario weapon that could occupy two roles - CQC assault weapon as well as a sniper rifle.

IMO, these are two different animals entirely. If you really want CQC (CQB), you want 16" or shorter - definitely not 20 in. Accuracy-wise, many 16's are more accurate than many 20's, and there is an ongoing controversy regarding whether 20's are inherently more accurate than 16's. (For a true sniper rifle, one could argue the merits of a 24").



ps: 1 MOA with iron sights is as good as it gets, regardless of barrel length!!

I have a 20" Hbar a3 bushy

With the standard handguard and varmint loads shooting w/ a scope from a bipod the groups would average around 3/4-1"

Now since i installed a free float tube w/ the same load and barrel (20" crome lined Hbar) it is holding 1/2" groups

Every little bit helps, I went w/ a vented DPMS free float tube (2 piece)

Thanks, Meat3rz,

That's the kind of information I was looking for.  Now, I'm sort of leaning toward just buying another upper with the 20,or 24", barrel so that I can switch back and forth.

Truthfully, though, if the 16" barrel did not make an appreciable difference in velocity, I'd just keep it and move one.  However, I'm currently of the opinion that the velocity loss is too much.

Thanks for your responses, I appreciate it.