I have tried that several times, and without perfected success. My attempts were to take a block of steel with a grooves cut into it. Lay the annealed brass across the grooves, lay 6 drill rods of same size opposing the grooves & put a plate of hardened steel over the bits & press them into the mold. This was successful & had 6 grooves into the brass plate. OK, I got the ribs.
First issue was keeping the drill rods Perfectly in place over the grooves so the press takes the rod into the groove. Got that figured out 2 ways. First was tape. Second was a wood block on each end retaining the rods precisely place same as the grooves. That worked well.
Next problem came when I pressed it into the round form, the ribs tend to flatten out some as I did this. It worked, but not as well as I would have liked. So the next idea was make a mandrel with ribs on it, then make a block opposite with clearance for the brass, for the round piece on the modified round mandrel & etc.
Well, I never got to that part, as I already had much more time into it than I could have taken a thicker piece of brass, formed the tube & filed of brass leaving the ribs. Bythe time I got tho this part, I realized I had worked 3-4 days figuring this out & making jigs & etc, I could have easily filed out a dozen of them by hand in a day.
Since it is not a pipe I would use allot, I didn't feel the effort was worth the time to make a forming mandrel & block & etc. to do this & continue making the jig.
But if you are like me & like lil jigs & such, it was something to try. I enjoy making the jigs as much as I do building rifles. But I tend to perfect ones that I will use allot & let the others go by the wayside.
Keith Lisle
PS: Actually 1st attempt was to punch the grooves into a grooved block, one groove at a time. This was time consuming, and the plate tends to warp as you make the next groove & as you proceed, it gets worse, thus why I tried pressing all 6 at once & ending up with a flat plate with grooves in it, prior to pressing it into a tube.