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    Bolt Airsoft B4 SOPMOD Recoil AEG


    Bolt Airsoft B4 SOPMOD Recoil AEG Review by Booligan

    Table of Contents:
    Basic Gun Information
    First impressions/Packaging
    Gun Specifications

    Bolt Airsoft is a relatively new company to appear on the airsoft scene, but they've come out with one hell of a product! The B4 SOPMOD is their newest AEG and it features a patented recoil shock system (BRSS) to give you solid recoil from an AEG platform. Built in Taiwan out of high quality materials, the B4 is a sturdy and reliable gun, built to take its own substantial firing forces with ease. I'll be going through this AEG inside and out in this review, so keep reading to find out more about the B4 SOPMOD!

    I first met with Bolt Airsoft at the Airsplat LA Retail Store Grand Opening event, where they had several models on display. I was able to get some trigger time with the B4, and was REALLY impressed with the way that it felt while firing. This gun was sent to me directly by Bolt in order to get the full Booligan review treatment. It is available at a variety of airsoft retailers including Airsplat, priced at $385 at the time of this review.

    Basic Gun Information:
    At its core, the B4 SOPMOD is a full metal M4 replica fitted with a crane stock, KAC style rail system, and equipped with Bolt's patented BRSS (Bolt Recoil Shock System) in order to give you recoil as well as bolt movement while firing. It's fitted with a buffer tube recoil weight which is actuated by the piston in order to replicate recoil forces like that of a small caliber firearm. You don't feel like you're firing a 12 gauge shotgun or anything like that, but it does feel a lot like firing a gas blowback rifle or one of the many .22lr AR pattern rifles out there.

    First impressions/Packaging:
    The B4 is packaged in a sturdy cardboard box with uses a system of velcro straps and foam cylinders to keep everything safe and secure during shipping. It was a nice change of pace from picking little pieces of styrofoam out of every part of the gun like I normally have to! Having previously shot the Bolt SOPMOD at the Airsplat Grand Opening event, I knew what to expect, but I still started grinning like an idiot as soon as I pulled it out of the box. I was impressed with how it felt in my hands then, and I'm still impressed with it now.

    Click on the individual thumbnails to see the full size photos

    Box art

    Along with the rifle itself, Bolt included a spare plug and rear wiring section (GREAT that this is included, more manufacturers should include spare parts like this), a few stickers, and a black steel flashhider. You will need to obtain your own battery, and I was told that the gun prefers 11.1v LiPo packs. I tested it with a 9.6v NiMH and 7.4v LiPo and found the performance lacking, so I'd recommend going with an 11.1v.

    Gun Specifications:
    Weight: 6.75 lbs
    Length: 31.75" - 35"
    Width: 2.5"
    Height: 10"
    Sight Radius: 15.5"
    Length of Pull: 11.5" – 14.75"

    At first glance, you can tell that this thing means serious business. From the matte black finish and engraved trademarks, to the rail system and crane stock, this thing looks every bit as realistic as a real AR.

    Overview, left side
    Overview, right side

    The stock is a crane type unit which serves at the battery compartment for this AEG. Due to the recoil system inside the buffer tube, you have to use the two compartments on the side of the stock to hold your battery. To access the compartment, you push the tabs at the bottom of the butt stock and pull it off. You can then take out the plastic filler piece and stick your battery inside. The gun uses a metal 6 position buffer tube with a unique wire routing design. Lastly, you'll find a single QD sling mounting point at the base of the stock.

    Buffer tube and wiring
    QD sling mount point

    The receiver is a standard M4 type unit with metal upper and lower receivers. Pulling back the charging handle will pop open the dust cover and retract the faux bolt carrier, exposing the hop-up adjuster. The controls are all located in the standard places, with the selector switch on the left side and the magazine release on the right.

    Receiver, left side
    Receiver, right side
    Charging handle pulled back, exposing the hop-up adjuster

    The pistol grip is a standard M4 unit with a ventilated base for cool operation. The grip has metal screw inserts as well as a metal inner base frame to keep everything intact and safe from the B4's firing forces.

    Pistol grip
    Ventilated base

    The B4 SOPMOD uses a KAC type railed handguard with plenty of 20mm rails for mounting your accessories. Mine had some slight rotational free play which was due to the delta ring being slightly too loose. I tightened it up one notch and it took out all of the free play.

    Rail system
    Bottom section removed

    The outer barrel is a one piece metal unit that has an oddly green tint to it in certain lighting conditions. It's terminated in a 14mm- threaded muzzle so mounting optional muzzle devices is a piece of cake. Bolt includes a black steel birdcage flashhider in the package, which is a very nice touch!

    Outer barrel

    The B4 is easy to aim using the standard triangle type front sight and chopped carry handle rear sight. Both sights are made of metal and are adjustable for windage and elevation. The upper receiver has nicely cut 20mm rails for mounting optics, however, you may need to remove the front sight if you go with certain sights.

    Front sight
    Rear sight
    Top rail

    The left side of the receiver has a few Bolt markings as well as a unique serial number. The serial number also shows regional markings indicating the target market of your specific gun. US guns are marked US, European Union guns are marked EU, etc. The right side of the gun has a small sticker with a QR code that links you to Bolt's website.

    Bolt markings
    Made in Taiwan
    Sticker with Bolt QR code

    The included magazine is a steel bodied hi-cap holding about 300 rounds. One nice feature of the Bolt design is that it's compatible with pretty much all standard AR magazines. I did have a few issues with some magazines not securely locking in, but I was able to solve this by placing a small amount of loop side velcro on the right side of the inner magwell surface. This pushed the magazine up further against the magazine catch and locked it in quite well.

    Steel bodied magazine
    Feeding end
    Winding wheel

    Performance after a 500 round break-in, using Airsplat .20g ammo is as follows:
    High FPS: 405.1 FPS
    Low FPS: 396.0 FPS
    Average FPS: 400.3 FPS

    Rate of fire will vary depending on the battery that you use, but with my Tenergy 11.1v 1000 mAh 20C LiPo pack that I use in most of my testing, I saw a solid 17 RPS using Audacity. Feeding was great after I took a little time to properly adjust the hop-up. It needs more hop-up than you think it would need, so don't hesitate cranking that dial down a bit. You may get double feeds if you leave the hop-up too loose.

    Range and accuracy using Airsplat .25g ammo was good, but not amazing. When I first tested out the gun, I could only consistently put shots on my torso sized target out to 135', but further than that, it didn't seem like it had enough hop-up effect to keep the round floating. I disassembled the gun and cleaned the hop-up bucking, which was quite greasy, and I saw an increase out to 155' quite consistently. That should be the first thing you do with this gun, as the bucking was very greasy.

    Accessing the gearbox does require a little more work than your standard AR, but it's not terribly difficult. You just need to make sure you're using the correct tools and doing things in the correct order. The big difference is with the buffer tube, as you don't unscrew it from inside like on a normal AR AEG. On the buffer tube locking ring, you'll want to use a buffer tube wrench or tap it loose with a flat head screwdriver. Before removing the buffer tube entirely, you need to remove the wire cover which is located on the bottom, and is secured with three phillips head screws. You can then pull out the wires from the connector which will allow you to pull it out of the buffer tube locking ring.

    Wire cover removed, note the great design keeping the wires separate.
    It's a small thing, but note the metal bracket inside the pistol grip, keeping everything VERY solid

    The gearbox is, more or less, a V2 with a modified top section to allow fitment of a blowback system. The blowback is piston driven and can be disabled if desired, separate from the recoil system. The recoil system uses a multi piece rod system which is hit by an aluminum disk located inside the piston to push back the recoil weight located inside the buffer tube. Nothing is connected solidly, so you don't need to worry about a jam in the system causing havoc inside the gearbox.

    Gearbox, right side
    Gearbox, left side
    Metal selector switch
    Blowback assembly
    Shot at the recoil weight system located in the buffer tube

    Inside the gearbox, you'll find metal bushings which appear to be 6mm in size, steel gears, a very lightweight, skeletonized aluminum piston, ported aluminum piston head, aluminum cylinder head, ported cylinder, and flexible tappet plate. The airseal is amazing, with almost no piston movement possible while plugging the air nozzle. The gears are well manufactured, but the bevel gear has a funky design that doesn't use a separate set of stop points for the anti-reversal latch. The AR latch is a shortened design, and is a royal pain in the ass to install. There is a black plastic spring guide with a metal washer acting as a rudimentary bearing system. The recoil rod goes through the spring guide and keeps everything nice and centered.

    Inside the gearbox
    Bolt marking on gear
    Aluminum lightweight piston
    Steel teeth
    Ported head
    Aluminum cylinder head and plastic air nozzle
    Funky gear design
    Recoil rod acts like a spring guide

    The motor is a high torque unit and has pretty strong magnets in it, keeping it from turning easily. It seems to do a good job with the current gearbox setup.


    The B4 uses a large rotary style adjustable hop-up fitted onto a 275mm inner barrel. The inner barrel is quite short for the outer barrel length, about 100mm shorter than it could be. It's marked as being a "6.0" bore, but I don't know whether it's a tightbore or not. The gun has a standard bucking and nub design, however, the nub itself is quite large and soft.

    Hop-up and barrel
    Short overall length
    Rotary style adjuster

    The great part about the B4 SOPMOD is that it's pretty much just an M4 at heart, and as such, is largely compatible with the multitude of internal and external components out on the market. One nice feature of this gun is that it is rear wired, so you can modify the front end with a variety of rail systems or other options, unlike the front wired RM4.

    Great recoil effect from the BRSS system
    Largely compatible with aftermarket components
    Rear wired so you can modify the front end with ease
    Field ready performance out of the box
    Sturdy internal components
    Rock solid rail system, unlike some other delta ring mounted units
    No creaks or wobbles in the body, however, you might want to tighten up your delta ring if it's loose
    Designed to run a LiPo battery from the factory

    Disassembly is a little tricky due to the recoil system and rear wiring
    Rate of fire is a little low with my standard LiPo test battery
    Battery space in the crane stock is a little tight
    Some magazines would pop out on their own, but I fixed it easily
    Requires tools some users might not have to fully disassemble

    We're in the middle of a huge surge in unique, state of the art gun designs, and the Bolt B4 SOPMOD is certainly right up there with the newest guns put out by the "big guys" of the sport. It has very solid internals and externals, good performance, and the recoil feature is a nice little add on making it feel more realistic. After meeting with Bolt and talking about some of their upcoming products, I'm eagerly anticipating seeing what else they can come up with!

    Many thanks again to Bolt Airsoft, and of course, Airsoft Retreat!