I have a DPMS Oracle that has a gas block installed from the factory and I wanted to change it to a standard A2 sight. Problem is the barrel isn't set up the hold the taper pins on the A2 sight. Anyone have any advice on how I can cut the channel on the barrel to hold the taper pin and how to locate where it needs to be? I have a flip up front sight on it now, but it's so far off I can't get the windage adjusted on the rear sight to even hit a 50yd target... I'm puzzled! I already have a new A2 front sight ready to go. Dummy me, I didn't look at the bottom of the barrel to see if the reliefs were in the same location. There NOT...And I don't want to buy a new barrel until I have too. Thanks for any help you can give me.
Danny

You can mount the FSB and mark where you will have to drill, but I would take it to a pro armorer.

+1.
Bring it to a gunsmith

Bring it to a gunsmith taper pins are pain to drill. I have built several uppers and I always have a competent gunsmith drill the taper pins. Also since you are using a flat top upper make sure your A2 sight is F marked, otherwise you will need a new front sight pin that is .040 higher to sight it in correctly.

The reason you are having issues sighting it in is because the Oracle gas block is lower than the flat top, the rifle in question is designed for a scope only with no BUIS. Another option is to go to a low pro gas block and run a free float tube that the front sight can be mounted too.

Here are two links Taper Pins
Second is what I'm doing Mill flats for set screw

Stone

The front sight I have is marked "F". The link you sent on taper pins said they use straight pins?? I have use of a lathe and milling machine. The rear groove for the gas block I believe is in the right place, just not tapered. I'll have to redress it to a taper, but I'll have to cut the front one. We'll see how the rear one comes out first. I have the use if some side milling bits used for hard tubing. Should work on a barrel if I work it slow with a lot of lube. I'm going to try it myself. If I mess it up, I'll but the gas block back on and cover up my mistake. Can't pay the cost of a gunsmith anyway, I'm retired I figure it will need a new barrel one day as much as I shoot it, so I'll spend the money to replace it with a chrome bore and an A2 sight already on it.
I'll let you know how it comes out. Who knows, I may have an A2 "F" marked sight someone may need soon...