Greetings gents and ladies....attempting to machine out some bar stock to create a free float hand rail. My question is....how do you all think these vendors are removing the inner material of a longer free float rail?

Standard drill bits won't work well at those deep lengths. Are they broached? or maybe extruded like that from the getgo?

EDIT (taken from post below):

Ah thanks. Guess I should specify a little better... I'm looking to make the interior an octagon. Then hog out the material under the picatinny for weight reasons. So the inner cutout would be an octagon with an upside down U on the top octagon edge. Guessing I'm going to have to get custom extrusion die for this right? Or would broaching be cheaper?

Extrusions.  I've got six blank extrusions sitting down in my basement.  I'll get around to machining a few of them eventually.

This.

Except I don't have any blanks.

Ah thanks. Guess I should specify a little better... I'm looking to make the interior an octagon. Then hog out the material under the picatinny for weight reasons. So the inner cutout would be an octagon with an upside down U on the top octagon edge. Guessing I'm going to have to get custom extrusion die for this right? Or would broaching be cheaper?

It's going to be very cost prohibitive to make anything other than a round rail.

Might call Shapiro metals in St Louis or contact Jackson Tube Service in Ohio.  If no one has it in stock might be easier/more cost effective  to bend it up from flat sheet and tig it. Then just get pic rail stock to add on

Thanks for the response, jstaley. Is that a common practice in the industry to bend and tig? I like the idea...just hit it with a final pass to clean the weld. I worry about the interior though not being clean.

So SLR Rifleworks for example....all of those have to come from a custom die extrude right? I'm assuming those guys are just buying the extrude (hollow octagon with picatinny hollow) then machining the outside?
I would love to ramp up to large scale at some point if possible. I have the funding and design ready to roll. Just need to get the fabrication steps down.

Also for example...Samson's Evolution rail with the spline through it...that's got to be from a custom extrude right?

They're all from extrusions.  A lot of the octagonal ones are actually round on the inside.  Other than some prototypes, no one is making handguards from billet.  No one would be willing to pay the price they'd have to charge for that.

For a one off or functional prototyping...bending from flat sheet and tiging the octagon is just more cost effective if you cant locate an off the shelf octogon tube.   Like others have said custom extrusions will get pricey.  Doubt you'd find a  metal sinter  3d printer that could handle something handguard size and keeping final dimensions in tolerance would probably take several prints and waste cash.

Dont go by Shapiro's web catalog, they do recycling too so they may have scrap/cut drops and you need to call/email.