I have a YHM flip up FS/gas block on it's way to me and I have an installation question.  Please tell me if I am wrong, but it looks to me that there is not a part of the block that will index the hole properly on the barrel.  I would like to know the best way to install this block properly in order to line uip the holes.

That is one heck of a question.  I too would like to know the answer.

I put the barrel on an upper reciever with a flip up rear sight, and put the YHM folding front sight on loose enough so it would rotate when needed. Then I put both flip sights up, and put the upper assembly upside down on a table, so it set on the front and rear sights. The upper rested on the protective "ears" of the rear sight, and all I had to do was rotate the front sight until it too rested squarely on its "ears". Tighten the screws and you should be set.

I made a very small mark on the barrel up on the step that was centered with the gas port on the barrel. (Used aa center punch)
Put the FSB gas block in place loosely with the gas tube inserted.
Lined up the gas tube centered over the mark as close as possible.
Snugged up the sight just a tad bit more.
With the upper in the vise, I looked down the picatinny rail on top from the rear to see how close the front sight was to being perfectly vertical.  
Gently tapped to one side with a small block of wood to tweak it to visually straight.
Made sure the gas tube was reasonably centered over the mark and tightend the screws on the FSB.
Took to the range and tested it.
Perfect function and didn't need any windage adjustment on a centered rear sight.

It took longer to write this than to install the sight.

I thought that I would update this thread.  I succefully installed a YHM gas block with flip up sight, a YHM forarm,and a ARMS 40 rear flip up sight.  I just got back from the range were I shot 260 rnds of Wolf 55grn with NO problems.  Was grouping around 1.5" at 50 yrds.  Thanks for the tips in this install.   http://www.hunt101.com/img/330942-big.JPG

Is that an H-BAR??  I am wondering because I also have a 16" Bushy HBAR and would like to know if the YHM sight base would work on this rifle.

Thanks

Oh...hello all!!

Yes it is a h-bar and the YHM sight/ gas block fits fine.

Thanks for the info!

Nice job, Looks really good!

Can one of these sights be used with standard handgaurds (i.e. with a delta ring and handguard cap)??   I've never seen this combination.

Thanks