Gas Blocks

AR/M4 AR Technical Discussion
1

Hello

I want to have someone school me on gas blocks!!!

I am a armorer (M-16 Colt) for my police department but I enjoy building AR’S for myself.

I recently have this urge to build or change on of my rifles to a extended Troy Ind MRF forend or something simular. but I have a problem I know nothing about gas blocks or removing front sight bases or even what blocks to use or how they attach.

How do they attach?
Which one are rock solid?
Do I buy a new barrel of use an existing?
If I do buy new what do I need does it need to be drilled for front sight post or not?
How do I remove the FSB.

Thanks for you time

Patrick

2

Patrick,
The factory A post FSB/gas block is the most reliable. I install aftermarket gas blocks (I prefer Larue & PRI) but I drill the barrel so that the set screws cannot walk and use Rocksett on the set screws. I have never had one move but I’m still of the opinion that the very best are taper pins. Most taper pins remove and install from the right side. CMT/Stag are removed from the left, why they have to be different I don’t know. I’ve given up trying to knock them out. If customers want them changed out I just cut the factory A post/FSB off with a cutoff wheel (on CMT/Stag barrels).

Robb

3

Where do the set screws go to on the barrel through the taper pin holes or flat on the bottom of the barrel?

I assume flat on the bottom of the barrel becacuse you are drilling a small hole the size of the set screw I would think so it will not walk.

Is there a gas block system that uses the taper pin holes for allignment I think this would be the most effective mount?

4

Most gas blocks that use set screws, screw in from the bottom of the gas block. I drill about 1/64th to 1/32nd into the barrel.

I don’t know of any aftermarket gas blocks using factory taper pins.

5

I’ve seen set screws go in the bottom and also on the sides (four - two each side one fore and one aft) – I am partial to the from the below – as it allows alignment that does not depend on screw tension.

I personally prefer taper pin setups – however KAC, GG&G and Noveske are the one ones I know that do it – all factory done.

I will only run set screw systems on low profile gas blocks under a rail - sine they wont have any impact issues.

6

As already posted, I dimple the barrel, and install a low profile (I like the Vltor) gasblock making sure the setscrew is secured in place with loctite. Use the current barrel if its decent, and leave the gas port alone. There are also rails which will wrap around your existing FSB if that is something you are interested in.

Like Kevin commented already, the only time its worth using a non-pinned gas block is when you are installing a rail over the top for protection.

7

Thanks

for posting the responses to my qiestion I have a much better idea of what to do and not do. I think I will have the gas block done by a factory.

8

Best value for a GB is the MI. It is also a quality unit. My favorites are the VLTOR/Noveske and LT.

If your going with a low profile GB I would get a rail that run over it because it just isn’t worth it otherwise (keep the FSB).

C4

9

Patrick,

Gas blocks are not that tough really…

The echo Grant, the best block on the market (imho) is the screw/pin block made by Vltor for Noveske Rifleworks – sorry for the crappy picture, but I can’t find my camera (not that it would be any better) so this is the old lay it on the scanner trick.

This GB uses a single set screw to align and secure the gas port, and a single cross pin to make sure the block stays in place

It is made from hardened SS and is all you really need for a gas manifold application.

10

KL, that’s pretty interesting. It just uses on of the taper pin holes that are already in the barrel?

11

A word to the wise.

While I’ve never had a set screw secured low profile gas block come loose myself, several people that I trust without question tell me it’s a bad idea on a “serious” rifle. They apparently have seen it happen with disastrous consequences.

I have LT’s on two carbines now, but both will be going to Adco shortly to be permanently pinned in place. I’ve been meaning to get it done for the past year, but it just slipped my mind. It’s only costs $25 so it’s worth the piece of mind.

12

gotm4 – you have to drill for the pin, so you need (want) a virgin barrel, the block is not very long and will not cover up old pin holes from a FSB.

VA Dinger – that is what is nice about the set up in the picture, you get the advantage of a set screw (you can line up on a dimple that mirrors the gas port and cinch it down) and you get the security of a pin to make sure it does not move… I have seen set screw blocks move and make the gun a single shot, some of the blocks out there are pretty soft metal and like those who you mention, I would not trust just set screws.