Building an AR platform rifle appears to be easy at first look. It is essentially a tinker toy for adults.
While you are collecting your parts one of the easiest to overlook is the gas block.
The Gas block is the interface between the barrel and the gas tube. The gas block may look as simple as a band around the barrel to a triangular front sight base. It regulates the amount of gas coming out of the barrel and directs the gas into the gas tube, then to the bolt carrier group. And for something as simple as it looks the decision you make determines how your rifle functions. The gas block is the part you buy after your receivers when you decide what kind of AR you want to build.
Decide first, do I want an adjustable gas block or not?
Do you want less recoil?
Will you be running a suppressor, subsonic ammunition, differing bullet types ranging from light for caliber, to heavy?
If the answers to any of these are yes, an adjustable gas block is in your future.
It is easy to fail to think your project all the way through and buy parts you don’t need. It can be as simple as buying a gas block you like, then finding your barrel is too big or small to fit. Barrels typically come in sizes ranging from .625 to .936. The most common diameter, .750 medium contour at the gas port. Sometimes what you want doesn’t fit together. It requires defining what you want to do, and then buy the parts.
Types and materials
There are two basic types of gas blocks. Slip on, machined as a 1-piece housing. Pins or screws hold these; and clamp on which usually uses two screws to maintain tension.
The most common material is steel and stainless steel. There are some made from aluminum and of course Titanium which is much more expensive.
I am also not aware of any titanium adjustable gas blocks.
Aluminum, in contact with high-temperature gas wears quickly. If you are building a rifle and need to remove grams to make weight for match regulations, then possibly it’s an option for you.
I know of no aluminum adjustable gas blocks I’d recommend.
I'm going to list the four best adjustable gas blocks, why I like them and why you should consider them for your project.
1. Superlative Arms .750 Adjustable Gas Block
The Superlative Arms patent pending “Bleed Off”, direct impingement, gas block for the AR15 platform adjusts the gas flow by bleeding the gas out of the block instead of restricting the flow like conventional adjustable blocks.
- The pressure used in the block is reduced only to the amount required to drive the bolt carrier. The remaining gas / pressure are bled out of the block allowing the system to run much cleaner and cooler.
- Reduction of felt recoil.
- Patent pending adjustment detent is located outside of the block and therefore no contamination.
- The gas adjustment screw does not restrict the gas flow; therefore there is no erosion or seizing of the screw / no loss of detent due to carbon build up. Although it is removable, we have added a safety mechanism, which stops you from unintentionally backing the screw all the way out.
- When using SBR’s and / or suppressors the bleed off port allows the excessive pressure to be exhausted out of the block reducing blow back.
This is a clamp on gas block, and if you are going to use a suppressor, this is the gas block to use.
Unlike most other gas blocks, this one vents excess gas out the front of the block, not over-gassing the receiver and battering the working parts of the upper. Doing this allows you to meter just enough gas to drive the bolt carrier. In turn, this reduces felt recoil.
Honestly, in 35 years of using this platform, I've never considered recoil to be a problem.
The gas adjustment screw doesn’t contact the hot gasses; therefore, it doesn't contaminate or seize from high-temperature gas.
In case you get too aggressive with the wrench there is a safety feature so you can’t back the screw out, an excellent idea for people like me.
And it's a low profile, so it fits under most handguards.
SBR and AR pistols, this will fix over gassing problems and not vent hot gas into your face out the ejection port of your upper receiver.
It isn’t perfect, but for what it's designed for I don't know of better.
2. Seekins Precision .750 Adjustable Gas Block
The Seekins Precision Adjustable Gas Block lets you to fine tune your rifle's gas system for smoother cycling and operation. Regulating the amount of gas used to cycle the action allows tuning the rifle’s operation to a specific load and the use of low mass bolt carriers, buffers and springs to reduce felt recoil. This is critical to allow faster follow up shots, target acquisition and reliability.
The Seekins Precision Adjustable Gas Block is field adjustable. Operation is easy, simply turn the gas regulating screw in to lessen the amount of gas and out to add more gas, then use the brass set screw to lock the setting in place. The overall height of the gas block is 1.37” with left to right dimensions at .94” to fit under most hand guards and still have the customization of an adjustable gas block.
Melonite Coated to reduce wear and corrosion for extended periods of fire, it also makes cleaning easier, as carbon build up will not adhere to the non-reflective coated surface as much as it does on standard Parkerized finishes.
I like the Seekins Precision block. It is made of steel, is a slip-on type and held in place with two screws on the bottom. When you order your barrel have the maker mill a flat spot for the screws to butt against; you'll never have a problem when the barrel/gas block heats up during long strings of fire.
It uses a brass friction screw, so no thread locker is necessary and won't mar the adjustment screw.
It's another low-profile type and fits under most handguards.
3. J-P Enterprises Adjustable Gas Block
The JP Enterprises .750 Adjustable Gas System And A2-Type Clamp-On Sight is a front sight assembly that replaces existing pin-on assemblies to provide the option of gas adjustment. Perfect for a competition build, this A2 front sight bolts onto a barrel, no drilling or pinning required.
The JP Enterprises .750 Adjustable Gas System and A2-Type Clamp-On Sight features a sturdy seal to provide better heat dissipation around the gas port as well as an easy-access side gas adjustment.
I included this block because I am a fan of NRA Service Rifle Matches which REQUIRE the external features of the M16. It must have a front sight block, no rail or folding sights.
Why would you need an adjustable gas block shooting a match?
Match rules state you must use the same rifle through the match, but you can change bullet weights for the different stages of the match. An easy, repeatable gas block allows very heavy bullets, loaded one at a time, to function the rifle without beating it to death. You need enough gas to get the bolt back and locked open to load the next round.
Setting it to function the rifle normally during the other two stages is an easy adjustment.
4. J-P Enterprises .936 Adjustable Bull Barrel Gas Block
This JP Enterprises Adjustable Gas System mounts securely because of the locking adjustment feature, which consists of an integral brass set screw that can be tensioned against the adjustment screw after it has been set. These gas systems provide better heat dispersal due to full coverage sealing around the gas port.
The JP Enterprises Adjustable Gas Block Model JPGS-8 provides one more way to make your gun perform like a champ.
If you are building a heavy barreled rifle, it is available in .936, so your barrel can run a straight taper from breech to muzzle. In the .936 it is a low-profile configuration.
5. Odin Works Adjustable Gas Block
The Odin Work's low profile adjustable gas block is manufactured to ensure the proper function of the gas system. It is engineered for suppressed/unsuppressed configurations with 20 adjustment points allowing optimal operations settings.
- Not for use with pistol length gas systems and high pressure rounds.
- Fits inside all ODIN Works Forends.
- Fits .750" diameter barrels.
- Weight: 2.10 oz (includes detent ball, screws and pin).
- Made from Carbon Steel.
- Nitride finish.
- Inconel adjustment screw and spring.
- 20 adjustments.
- Includes detent ball, cross pin, set screws, and hex wrenches.
I list the Odin Works last because it is NOT suitable for pistol length gas systems. However, it is an excellent gas block for the shooter who wants repeatable adjustments when changing bullet weights.
If you are the type of shooter wanting a very heavy bullet for hunting, then shooting the less expensive 55-grain ball for plinking and light target work this is the gas block for you.
It has 20 detents for repeatable settings, machined from steel and nitride coated.
A general- purpose rifle needs a general-purpose gas system; the Odin Works gas block does it all.
It's rated for any caliber, 308 included.
An adjustable gas block is one of the most critical parts of your rifle build and should be chosen carefully for the use you envision for your new rifle.