Here's the deal. I have a standard A2 FSB that I want to remove, and replace with a low profile gas block/FSB with a rail on it. I understand that the factory FSB is custom fit / indexed to the barrel with two pins.

Are there any railed FSB/Gas Block combos on the market out there which make use of set screws and can be installed without custom fitting or removing metal, and which are compatible with flip-up front sights and will reliably hold a zero?

You might want to check out PRI and Yankee hill machine, they both make a flip up sight/ gas block combo. They are both the clamp on style which are easy to install and adjust to zero the rifle. I happen to have the PRI unit and it seems to hold it's zero well for a back up sight.  Hope the info was helpfull .      PATRIOT ARMORY 07 FFL

if you want a flip up front sight i would steer you in the pri direction.


no point of having a railed gas block and a flip sight to mount on it when you can have the whole package with less hassle

Will the PRI flip-up match up with the ARMS #40 on a flattop?

PRI & A.R.M.S. #40, perfect match. Ihave been using this setup for a few years now.   Works great for me.  Give them a try , i'll think you will like the setup.    PATRIOT ARMORY 07 FFL

Quoted: if you want a flip up front sight i would steer you in the pri direction. no point of having a railed gas block and a flip sight to mount on it when you can have the whole package with less hassle

+1

I'm looking into those. The price is making me raise an eyebrow though. How can these cost so much?

Also, any advice on mounting something like a Burris black diamond when part of the rail is taken up by the ARMS BUIS? What type of mounting rings or risers should I be looking at?