Just thought I'd throw this out here as I was apprehensive about it, but it was complete cake.
Geissele did very well with this, follow their instructions, use a short rigid bit, use lube, go slow,
and eyeball the alignment carefully.  Worked like a charm despite my obviously shade-tree metal
cutting skills and equipment.











screenshot

Im really considering this gas block.  What rail is going over this?

Nice

What make/model drill press ?

Sir, those photos are wonderful. This has inspired me and I hope it inspires others.

What kind of block is that underneath? I'm most intrigued by that.

Nice work!

The socket?

Oh, the one with all the markings.

+1.  I did the same thing this weekend with the same block.  

What made it easier for me was the Geissele instructions including the exact McMaster-Carr part numbers for the two drill bits (dimple and cross-pn) and the end mill to create a flat on the barrel to prevent the cross-pin drill walking sideways.  Knowing I had the "right" tools helped take some of the edge off of the first-timer nervousness.

FWIW:  The instructions recommend using the end mill to create a flat surface for the cross-pin drill bit to start on if you are drilling a nitrited barrel, to help avoid the drill bit being pushed sideways by the hard surface.  I was drilling a stainless Ballistic Advantage barrel, and I don't believe I really "needed" it.  That said, I'm very glad I ordered it -- it was such a perfect fit for the block's undersized (pre-final drilling) cross-pin holes that it helped with eyeballing the alignment (i.e., checking block alignment by advancing mill in the not-running drill press while tweaking the vise position until there was no mill/hole wall contact).  

The end mil also went through the stainless barrel material so smoothly (with cutting fluid and slow feed rate) that I just kept advancing/withdrawing/advancing the end mill all of the way through to the other side of the barrel.  That left a perfectly straight hole all of the way through the block/barrel to help guide the final 13/16" drill.

That must be ugly...

Yikes.

Gas block came with the rail, Geissele Mk8, great deal imo.

This one: http://www.amazon.com/gp/product/B00HQONFY6?psc=1&redirect=true&ref_=oh_aui_search_detailpage

I replaced the chuck and arbor, and it cost almost as much as the drill press itself, but it upped my precision a bit.  South Bend Lathe parts, chinese still but better than
what it came with I think.  Also the included belt was crap and the "laser" alignment stuff is junk.  It is what it is, but for under $300 shipped it's OK.

I learned in the course of researching and buying a drill press and doing some 80% lowers, that any drill press under $1K is not precise. :)
But, if you are super, super, super careful you can get reasonable results form a budget model if your expectations are reasonable.
I also do a lot of mechanic/handyman stuff so it's been a good investment.  Just tonight I drilled out the holes for a crank pulley holder
for a timing belt change on an old car.  Could have done it with a hand drill, but it was nice to toss it on the press and be done.

This guy?  http://www.primaryarms.com/156945/p/156945/

Works well, I've removed two FSB with it, works as described.  If have a barrel block thing from them too, works well for my
non-professional use.  :)

I don't have any experience doing this with other gas blocks, but it really was cake with this one.  I don't mean to be brag since it was easy but I was really apprehensive about it and as it turns out it was
super easy, so I figured I'd post it up.  I used a lot of align-by-feel of the bit and it was very intuitive, mine was a Sionics standard steel and it cut like butter with plain HSS bits and lube.
And I didn't kill the barrel which was the best part. :)