I've only recently done this for the first time, and it was kind of by accident. I purchased a VVCG 15" Stainless-Steel Barrel in 6mm T/CU, and requested the forend spacing for a Super 16 Forend. I picked up a Rynite Super 16 Forend, and it wouldn't fit as the factory Super 16 Barrels are slightly tapered. I found the right size dowel and wrapped it with sandpaper, and sanded out the barrel channel till it fit the barrel. The result ended up with a forend that only touched the barrel on the two saddles where the attaching screws go through the forend. This barrel shot so great (not really sure if it is just cause of the free floating or because of the barrel) but I did a Rynite Super 14 Forend the same way.
I used the Super 14 Free Floated Rynite Forend on a Super 14 Match Grade .22 LR Barrel for a while until I aquired another Frame. The frame I aquired had the older style Herrett Walnut Finger Groove Grip and matching Walnut Forend. On this new Frame the groups opened up considerablly, and I thought it was the Frame (different frame to barrel gap / headspace) until I tried it with the Rynite Forend. With the Free Floated Rynite Forend the groups went right back to where they were to start with.
I have since free floated the Walnut forend and installed pillars inside of the countersunk holes in the bottom of the forend for the barrel to sit on. While I haven't had the opportunity to test it with this newly Free Floated Forend YET hopefully this will work out as well as the Free Floated Rynite forend did.
Sorry I couldn't be more help, maybe someone with a little more experience in this area will respond.
Good luck
Larry
Larry