Gas block installs and why you should be dimpling the barrel

[mtdawg169]

When your local LE has to use a junk upper on duty, because it's that or nothing at all, you fix it and hope it gets put to good use one day.

Great example of what can go wrong with something as simple as a gas block install. Nitride barrel, cheapo low profile gas block with cup tipped screws. The barrel is so hard that the screws can't bite into it. So it moved forward and the gun became a one-shot wonder. Removed gas block, dimpled barrel, replace screws with aggressive knurl tipped screws, reinstall with red loctite. It's not going anywhere now!

 

[cooter]

I've seen people cut down an a2 sight and shape it the same as a lopro gas block so it could be pinned back on the barrel. Will the aggresive tipped screws hold as well as going through that much work?

 

[mtdawg169]

I've seen people cut down an a2 sight and shape it the same as a lopro gas block so it could be pinned back on the barrel. Will the aggresive tipped screws hold as well as going through that much work?

Cutting down a fixed FSB is a great option, if done correctly. Two steel taper pins will always be stronger than a set screw. But for a virgin barrel that will be used in a low profile configuration with the block under the rail, a dimpled barrel with the correct screws is pretty darn rugged. Or, you can pin the low profile gas block with a single taper pin if you have the right fixtures and tooling, including a 2/0 taper reamer. Pinning will always be stronger. The dimple and screw method is very secure though.

What you don't want to do, is just slide the block on and tighten the screws. Not using a dimple means that you're relying totally on tension to secure the block. It's the least secure method for installation. The addition of a dimple creates a mechanical lock of the block to the barrel. Which prevents the block from moving or rotating, even under heavy use.

To do this correctly, you will need a dimpling jig from someone like BRDE or SLR Rifleworks.

 

[mtdawg169]

Following up on this thread with tutorial

OK, here we go...

Using a Geissele gas block. The set screw spacing on the most common gas blocks is usually either 0.40 or 0.45". The BRDE jig is set up for 0.45 spacing. However, the SLR Rifleworks jigs allow for both by simply flipping the jig over and swapping the screws.

One thing to note here is that the port on the Geissele block is fairly small, so there is little room for error in terms of alignment. BCM & Vltor blocks have a significantly larger port which gives you more leeway. As a result, using a jig in this case is especially useful.

Distance from edge of block to leading edge of gas block port

Compared to the gas port on the barrel

Here, you can see the port aligns directly with the rear set screw hole.

The jig. 0.40 side facing up. The jig has two screws. One has a pointed tip, that indexes and self-centers on the gas port. The other, is a large cap head screw with a guide hole drilled right down the center.

 

[mtdawg169]

Alignment screw with jig installed on the barrel

Guide screw

Installed in the vice

I don't have three hands, so no action shots. Here's the finished product.
Totally ruined...

Perfectly aligned

And the finishing touch is using the correct set screws with an aggressive knurling on the tip

I found this turd on the floor after dropping the set screw shown above. This is an example of what NOT to use. I'm pretty sure I threw it on the floor after swapping it for a knurled tip screw a couple of months ago. It came off of a PD gun that didn't cycle. I'll give you one guess why it didn't run.
Hint: look at Post #1

Duce's barrel in all of its engraved (and dimpled) glory!

Also interesting, here you can see that the Geissele block is compatible with a barrel pin. You can see that it would engage about half the width of the pin, which I prefer over a deeper set pin that drills completely through the barrel. Because: reasons.