Bolster Tuned Sig Sauer MPX Upgraded AEG

The Original SigAir MPX AEG

Starting at the tip of the 8-inch outer barrel we can find a birdcage flash hider attached to 14mm CCW male threading. The flash hider is constructed from alloy with a subtle gun metal grey finish and can be switched out for any 14mm CCW compatible muzzle device, including tracer units, suppressors and alternative flash hiders. 

The handguard of the MPX is constructed from aluminium and is finished with CNC machining, giving it a flawless form with all the details of the original firearm. M-LOK attachment slots can be found at the 3, 6, and 9 o’clock positions, providing plenty of options when it comes to accessorising the MPX without making the handguard uncomfortable to hold when kept simple. Punctuating the M-LOK slots we can see weight-reducing ports which keep the front end of the MPX lightweight and agile, ensuring you can point it quickly and react to sudden threats in a CQB environment. 

At the 12 o’clock position we have a 20mm Picatinny rail which is ready to accept any 20mm Picatinny accessories, including red dot sights and magnifiers. Despite its small size, there is plenty of room up top, and the monolithic top rail allows for a PEQ15, red dot sight and magnifier to be mounted a the same time if you are the type to deck your primary weapon out to the fullest extent. 

The battery compartment of the MPX is located inside the handguard and can be inserted through the front where you will find a Deans battery connector. Being the Bolster Tuned MPX, this platform has been thoroughly upgraded internally (details below) and can handle an 11.1V 1450mAh LiPo battery, providing an absolutely stunning rate of fire. Being front-wired also opens up the possibility of using the MPX with an external PEQ battery box and running a larger battery for those who like to spam the trigger all day without changing batteries. 

The MPX’s receiver is derived from the M4/AR-15 configuration and comprises an upper receiver and a lower receiver, just like the AR. The upper is a monolithic design for optimal strength, like the MCX and SCAR, and the lower is patterned after the M4/AR15 but with ambidextrous functionality. 

The fire selector is right where you would expect it; above the pistol grip, sitting right beneath the shooter's thumb for fast access. As with all of the controls on the MPX, the fire selector is present on both sides, making this SMG a great choice for a left-handed skirmisher or an experienced skirmisher who likes to be able to shoot from either shoulder to make the most of the surrounding cover. 

The familiarity continues with the magazine release, which is positioned on the magazine well on both sides of the MPX. This is a push button style design and is very similar to an M4/AR-15, meaning if you have experience with the M4 platform you will feel right at home with the MPX in your hands. 

The mock bolt release catch is also present on either side; with an M4/AR-15 style “ping pong paddle” on the left side, and a push button on the right just above the mag catch. The right side bolt release sits nicely within reach of the trigger finger, which is one of the more enviable aspects of the real MPX design. We wish more M4s had this built in, but for now the MPX will have to do! 

Once again, the charging handle of the MPX is located in the same place as it is on the M4/AR-15; at the top rear of the receiver. If this wasn’t a good spot for a charging handle we would suspect Sig of copying Armalite's homework! 

The difference between this and the standard M4 charging handle is its ambidextrous functionality, presenting two release tabs, one on either side which allows you to pull the charging handle with a single finger, whether you are left or right-handed. The charging handle does not need to be pulled to load the first BB, but it is used to lock the alloy mock bolt carrier back to allow for HOP-up adjustment. 

The HOP-up unit of the MPX is located inside the ejection port on the right side of the SMG, and is accessible when the charging handle is pulled back and the mock bolt is locked to the rear. This unit has a rotary style adjuster which is derived from the M4/AR-15 rotary HOP-up, which is great news both for those who use their guns as they are and those who like to upgrade. 

Adjusting the HOP-up allows you to tune the MPX for different ammo weights and extend the range of your BBs by applying backspin. With your HOP-up set so your BBs fly as straight as possible, you can release the mock bolt using the bolt catches on either side and close the dust cover too if you are super tactical!

To assist in speedy reloads the MPX has an extremely wide magazine well flare, practically guaranteeing that you will never fumble a reload. The magwell flare also allows for easy and fast “eyes up” reloads with a bit of practice, making the MPX a great primary for the CQB specialist. On either side of this massive blank canvas of a magwell, we can find some lovely engraved SIG trademarks matching the real MPX faithfully; one of the many perks of an officially licensed replica! 

Like the magazine well, the trigger guard is also enlarged to allow for fast access to the trigger, even if you are wearing thick gloves. The original SigAir pistol grip has been replaced with the PTS EPG in this, the Bolster Tuned MPX. This was done to improve the motor engagement angle for reduced wear and to enhance handling qualities. The PTS EPG is one of our absolute favourite grip designs, but if you want to read more about it, check the "Upgrades and Tuning" section below. 

On either side of the receiver, we can see recesses designed for the original sliding MCX/MPX stock system, giving you the option of installing a sliding PDW-style stock to the MPX for a different look. The stock attachment method of the MPX is known as the “1913 rail stock attachment system”, which uses a 20mm Picatinny rail to mount the stock. This gives you a wide variety of aftermarket stock options to choose from, including simple skeletonised stocks for reduced weight, visor stocks for more comfortable use with large full face protection and even M4/AR-15 stocks which can be mounted with a 1913/20mm Picatinny buffer tube adapter. 

Upgrades and Tuning by Bolster Armouries

As with previous Bolster Tuned builds (formerly known as Patrol Base X Gate ASTER edition), this isn't your usual upgraded AEG. The Bolster Armouries tech team fully disassemble each of these AEGs down to every screw, bolt and bushing to perfectly tune the internals, polish the piston tracks and bearing holes, shim the gears to absolute perfection and replace parts to address the weak points in the original platform. The Bolster techs treat these AEGs like they are building them for themselves, and if it doesn't pass their rigorous checks, which include a 60m accuracy test, it goes back to the bench for more work.

The Gate TITAN V2 MOSFET system makes its first appearance in a Bolster Tuned platform, offering even more functions than the usual ASTER MOSFET present in these builds. The TITAN boasts programmable fire controls through the Gate Control Station app, Gate Blu-Link or Gate USB Link, adjustable pre-cocking for a ferocious trigger response in semi-auto, cycle timing control, adaptive active braking, adjustable trigger sensitivity, and voltage control, all of which combine to give this gorgeously built licenced replica a wealth of functionality that is hard to beat.

The TITAN is paired with the Maxx Model CNC Speed Trigger finished in metallic blue; a household name when it comes to snappy flat triggers. The Speed Trigger offers full trigger adjustment via the pair of grub screws in its base, meaning you can tune the trigger to eliminate overtravel and avoid unnecessary movement. This feature derives from real steel competition-optimised rifles where every millisecond counts. 

The Maxx model advanced speed trigger is specifically designed to facilitate a fast trigger response and a smooth and consistent trigger pull and can be adjusted at multiple points to control the trigger pre-travel and reduce over-travel. This trigger is designed to work well with the GATE TITAN MOSFET to provide practically instantaneous trigger response and an ultra-fast fire rate on semi-automatic.

The trigger is machined from a single piece of aircraft-grade aluminium using CNC processes, with a separate titanium pivot pin for maximum durability. The trigger shape is intended to provide a natural trigger position for the vast majority of hand sizes and has chamfered edges and three rubber pads to ensure comfort, enhance traction and provide positive control of the trigger. 

The motor installed is the Warhead Base 27K Brushless Motor, offering a super speedy motor which uses high strength, SH-rated Neodymium magnets. Being a brushless motor, the Warhead Base simply doesn't heat up as the only friction generated inside is with the air, keeping this cool and allowing you to let off some seriously long bursts guilt-free. The Warhead moves the Bolster Tuned MPX up to the next level of Airsoft performance and puts it hot on the heels of the full-fat Bolster Armouries ONYX, ARKOSE, ATLAS and OBIRE builds.

To ensure reliable feeding at its new astonishing rate of fire, the Bolster team installed the FPS Softair Carbon Fibre Reinforced Tappet Plate paired with an HS Delayer Chip. Ideal for a precise build which requires perfect nozzle alignment, the FPS tappet plate is constructed from carbon fibre-reinforced nylon polymer which has the perfect amount of rigidity and flex without being vulnerable to sudden fractures under heavy load as a conventional polycarbonate tappet might.

The tappet plate is an essential part when it comes to ensuring the AEG's internals are timed correctly and that feeding is smooth and constant. The FPS Tappet has an absolutely flawless shape and the perfect amount of strength while avoiding being so hard it becomes brittle. Its carbon fibre reinforced polymer gives it the edge in durability over every other tappet on the market. 

The HS Delayer Chip mounts to the sector gear of the Laylax EG 13:1 High Speed Gearset, ensuring everything stays well timed and feeding is consistent with the cycling of the gears. The EG Hard Gear Set from Laylax is constructed from hardened steel and is a high speed gearset intended to considerably increase rate of fire of any AEG into the realms of the extreme. These gears are leaps and bounds ahead of the original VFC/SigAir Gears in strength, making them a worthwhile inclusion for long-term reliability under the extreme performance parameters set by the Bolster Armouries team.

These gears are tuned to a 13:1 ratio, which means for every 13 revolutions of your motor the gearbox will complete one full cycle. The standard gear ratio for Airsoft AEGs is 18:1, meaning the Laylax High Speed set will give the Tuned MPX a far higher rate of fire than its rivals and allow the potential of the astonishingly fast Warhead Motor to really shine through.

The set includes a spur gear, sector gear, and bevel gear which are all precisely machined and shimmed to perfection by the Bolster team for flawless meshing and smooth, reliable performance. These high performance reinforced gears run on Bolster Armouries EZO Bearings to guarantee the perfect combination of strength and low friction. The EZO bearings allow the Laylax 13:1 High Speed gears to spin freely at the tremendous rate provided by the Warhead Brushless Motor with minimal chances of failure, all while reducing stress on the gearbox shell and gear axles.

The Bolster team cannot touch an AEG without installing their favourite HOP-up rubber, the legendary "Prommy Purple". Also known as the Laylax/Prometheus Purple HOP-up rubber and nub, this setup is based on the original Tokyo Marui design but comprised of more hard-wearing and temperature-resistant materials and is a big part of what allows the Tuned MPX to absolutely destroy the original when it comes to range and accuracy.

Finally, we're on to the ergonomic upgrades. The team chose the PTS Syndicate EPG Pistol Grip to replace the original pistol grip. While the original was a comfortable design and very authentic, its grip angle presents problems when it comes to motor engagement. In a high-performance, upgraded MPX, these problems only magnify. 

The EPG is constructed from Dupont Zytel, a high-strength, abrasion and impact-resistant thermoplastic polyamide/nylon, making it a significant step up from other high density polymers, even beating out the original SigAir pistol grip. With comfortable dot texturing on either side and crackle texture on the front strap and backstrap, the EPG is the perfect enhancement to ensure you maintain a positive grip on your MPX and allow the Warhead motor to engage properly with the Laylax 13:1 gearset. 

At the rear, we have the Laylax 1913/20mm Picatinny MCX Folding Stock, based on the stock used on the latest real steel MCX rifles but constructed from high density polymer with a button to fold it instead of the usual spring-loaded mech. This improves the handling of the MPX considerably, keeping the rear end light for faster target-to-target transitions and allowing the stock to be folded easily in an instant for when things get up close and personal. The stock folding button is present on the top of the aluminium hinge mechanism, and when the stock is folded, it locks into place securely. 

With a full internal overhaul carried out, the original MPX arrives exactly where it should be; an incredible shooter with gorgeous externals to match. If you've wanted an MPX but didn't pull the trigger for one reason or another, the Bolster Tuned Sig Sauer MPX Upgraded AEG is the MPX you deserve, and will make you glad you held off on the original!

Package Includes

• Bolster Tuned Sig Sauer MPX Upgraded AEG
• 100rnd Medium Capacity Magazine
• Gate TITAN PVC Patch
• User manual