I am in the process of installing a longer quad rail on my ar.  I know there are different types of mounting systems for the gas block but I need some advice on which brand to get and which mounting style to use.  Can anyone educate me on this?

any low profile block should work as long as it is the correct inside diameter for your barrel. No particular style is needed although I like the specter by YHM because I live in NJ. This allows me to remove the gas block while having the mandatory pinned muzzle brake. To each his own, my 9mm ar has a random budget low profile that i found online for 24 bucks. good luck!

http://gunsandammosuperstore.com/wp-content/uploads/2014/02/YHM-9378.jpg

What gas block is best depends on what the mounting options are on your barrel.

Gas blocks with set screws are great IF you have a barrel properly set up for them with a dimple on the bottom.

If it's not a dimpled barrel, I recommend the clamp style.  Then you need to take into account the type of handguard you're putting on, so how much room is available for the block.  Vltor and others make clamp on style low profile blocks.  Daniel Defense has the slimmest clamp on block, but the screws are harder to deal with (because they're smaller) and the DDs tend to be more expensive than some of the others.

If you have a pinned on front sight base and are 100% sure you never want to go back to the pinned on front sight, you can cut it down and make it into a low profile block.  To reiterate, pinned sight bases are NOT interchangeable, and once you destroy the one that came on the barrel you won't be able to replace it as a practical matter.

Pinned or Rocksett setscrews with dimpled barrel.

I like the YHM 9383 low profile gas block.  The screws supplied with it have small teeth that cut into the barrel and prevent them from backing out or the block from rotating.  Most the other companies just use standard set screws.        
 

i got a SS JP adjustable low pro clamp gas block on a build i just got done for 3 main reasons:
1) i got one stainless steel b/c it wont heat as fast as aluminum.
2) clamp style b/c i KNOW it wont loosen up on me compared to some set screw types ive had in the past.
3) adjustable b/c if i ever do get around to getting a suppressor, i can fine tune the gas system accordingly

worth every penny imo, if i do more builds i will probably fabricate my own block replicating the jp one i have now.

No decent quality gas block is made from aluminum.  



 

right, i agree, but they do exist. and for anyone trying to do a lightweight build or is trying to build on a budget, those cheaper, lighter gb's look better than a ss gb even tho they would be sacrificing quality.

I have used aluminum  railed and lo-pro gas blocks, that I bought at Surplus Arms, on several builds and I have not run into any problems.  I haven't done thousand round ammo dumps, or carbine courses with them, but I have not had any problems with regular shooting.  I think a lot of people hear things from their sister's boyfriend's cousin and perpetuate myths created by improperly installed parts.

How do you know if a barrel is dimpled??

Look at it?

What kind of barrel do you have?  A photo maybe?  Is it disassembled?

Ok...where on the barrel should I be looking?

I have a Wilson Arms SS 18" bull barrel.

Set screw dimples are under the set screws.

Opposite the gas port on the bottom of the barrel.

A google image search for "barrel dimpled for gas block" has dozens of photos.

Thanx...wil google.

I have used DD clamp on GB and the screws do suck.  I like a dimpled barrel and regular set screw with blue loc-tite and never had an issue.  There are a lot if good GB out there You just need to find what will best fill your needs and budget as they can be from $20 to $120.

If your barrel is not dimpled they sell a jig and and it is easy to do it yourself.