With so many options on the market, it's hard to really know which gas block type is actually best. So in this blog post we are actually gonna dive into all the pro's and con's of each and where we stand with our gas block choices.
So let's get started!
What is a Clamp-On gas block?
Well, it is exactly as it sounds, it is a gas block that achieves it's lock-up to the barrel by clamping around the barrel itself.
What about a Set-Screw gas block?
Once again, the name is a great indicator of how it achieves it's lock-up to the barrel. It uses 2 or 3 set screws directly underneath the barrel to pull the gas block down onto the barrel gas port.
Is one better than the other?
Yes and no... They both do the same job, but each has different properties which lend themselves better per application.
First, let's dive into the reason why the Set-Screw gas block is so popular!
Ease of use. (Dependent on presence of barrel dimple)
Manufacturing process/cost
Clearance inside Handguards.
To explain the ease of use, we must also dive into manufacturing process/cost. In order to drill the gas port hole for the gas block inside the barrel journal, you must first drill through the gas block journal via the bottom of the gas block.
This means you are now left with a hole directly underneath the gas port hole. Which itself is then threaded to be used as a set-screw hole.
In the manufacturing world, this is a "win" because this is 2 manufacturing steps completed within the same cut/drilling step. Less steps, means less setup, which translates to less time, and therefore reduced cost.
But also, because the threaded hole is exactly at the opposite end of the gas port hole, this means that if you dimple your barrel the gas block will self-align perfectly. Assuming you tighten the set screw in the dimple first and in the right place of course.
On top of self-aligning, this dimple provides lateral support to assist the gas block as to preventing it from moving out of place during use or abuse.
Sounds like perfection right?
Well....... Not really.... Let me explain.
Due to the nature of the set screw location, this means the set-screw itself must exert A LOT of concentrated force onto the underside of the barrel to pull it down on to the barrel gas port and hold it in place.
How do we know it's a lot? Well, considering the way these parts are held is based on friction, in order to achieve enough of it to stay in place you either need increased surface contact, or increased pressure. Sometimes both!
Considering all set-screw gas blocks are loose fit to the barrel, their contact surface is minimal. Which means they achieve the friction via increased pressure. One could argue that the gas block itself can flex to increase contact surface, but this must be done by applying even more pressure by the set-screws.
A pressure might I add, which is high enough to create an indent on the barrel surface itself... Think about that for a second...
Most of everybody would be freaking out about dropping their barrel on a rock and causing an indent on it. Yet somehow, if the gas block does it, "it's okay".
So how do we resolve this excess pressure?
The barrel dimple is a great way to reduce the required pressure, as it exchanges "friction" for a type of "physical lock-up". Which means technically one could reduce the amount of pressure/torque applied to the barrel and gas block.
But does anyone actually run less set-screw torque when using a dimple? No, not really...
Does this concentrated pressure even matter?
We believed it did to a point. So we took a spare Faxon barrel and gas block and decided to conduct a test!
The barrel used was a 10.5" pencil barrel with a .625 gas block journal with a matching Faxon .625 gas block.
The main reason for using this gas block was because of its "weight reduction" which allowed the barrel to be exposed on both sides. This exposure allows us to use a micrometer on the barrel itself after the gas block has been torqued into place.
So what were our results you ask?
As expected, after torquing the set screws to 28 in-lbs. We were able to achieve a barrel deformation of 0.0001". (After reviewing the testing footage we realized the original number written in this BLOG post of 0.0005" was a"typo". We edited the post on 02/25/24 to reflect the correct value which is 0.0001")
Is this enough to matter? The answer is: It varies per application.
It could have a huge effect, or it could be negligible. But it absolutely could be a factor for decreased barrel accuracy!
What we can also tell you for certain is that the barrel itself is a hollow tube. Which means whatever happens to the outside, must also happen to the inside.
And last time we checked, a 0.0001" deformation on a circle, means it's no longer perfectly round.
One could argue that it's not much of a deformation. However you must remember, this deformation was not present until we attached the gas block...
This "deformation prevention" is the primary reason why scope rings and hose clamps all use a clamp-on style attachment method. To simply grab ahold of the part via friction in a way that will not deform or damage the part itself.
So what about clamp-on gas blocks?
Clamp-on gas blocks have several benefits:
Conforms to the contour of the barrel.
Increases contact surface while applying most of the stress on to itself and not the barrel.
Creates a perfect gas seal against the barrel itself.
So if they are that good why don't people use them as much?
Pretty simple actually:
More steps to manufacture (increased cost)
Larger by design (difficult to fit inside some handguards)
No self-aligning features.
Common myths.
Wait. Common Myths?
Yessir! There is this common myth that a gas block needs a physical lock-up, like a dimple or a pin to stay in place.
"I don't recall the last time I saw a dimpled or pinned bolt carrier gas key."
I promise you the gas key survives through a way more violent environment then the gas block ever will. The gas key's job is not only directing gas, but also serves as an anti-rotation device for bolt locking and unlocking.
All of this while surviving the violent shock forces created during the cycling of the firearm.
Okay, so the clamp on is truly better, but how do you align the gas block and how do you pin it?
We at Eitri's Enhancements, LLC use tools such as levels, borescopes, simple measuring tools, and shims to get perfect alignment of these gas blocks.
As far as pinning the gas block? It's simply not necessary. The surface contact against the barrel is so large that the amount of force required to move it is astronomical.
But if you truly must make sure the gas block does not budge for peace-of-mind. We recommend the use of Loctite or Rocksett on the screws in conjunction with a torque wrench to get proper and even torque on the screws.
Then, if possible we suggest staking around the bolt head to add friction without affecting the bolt itself or clamp load. Similar to the way gas keys are staked.
Okay, but what about handguard fitment?
This is a big issue with clamp-on gas blocks.
To solve this problem with products we sell, we also offer Low-Profile screws for our preferred VLTOR Clamp-On Gas block which allow fitment inside handguards with an inner diameter as small as 1.3".
What about cost?
Unfortunately this is the part we cannot avoid.
Clamp-on gas blocks are simply more expensive to manufacture than set-screw style gas blocks. The only way to avoid this extra cost would be to have "press fit" gas blocks similar to what the AK platform uses. But even that requires the extra step of a pin because of tolerance stacking. As some press fit gas blocks may be tight enough but others may not, hence the pin.
The clamp-on gas block guarantees perfect fitment on the barrel by always applying the correct pressure, and conforming to the correct shape. Which is something a press-fit or set-screw gas block can never achieve.
For us, the benefits of the clamp-on style are definitely worth the increased cost. Which is why we use clamp-on gas blocks for all of our builds!
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