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Western Arms Infinity SV F3.9 Full Auto Pistol
  • Manufacturer 
     Western Arms
  • Model 
     Infinity SV F3.9
  • Capacity 
  • Weight 
  • Power 
  • Power Source 
     HFC134a / HFC22
  • Blowback 
  • Hop-up 
  • Shooting Mode 
     Semi, Full Auto
  • Construction 
     ABS plastic, Metal


+ Racy and tactical styling
+ High ROF
+ Good accuracy
+ Reliable Hicap design
+ Ability to use your old Hicap mags + Hi capacity magazine beats all full-autos on the market (when comparing stock magazine)


- Unable to use HFC22 reliably "out of the box"
- Slide a little light
- Lower than expected blowback kick
- Muzzle mount block not included but sold as an option


Highly tactical pistol can be used as a project gun for building the ultimate machine pistol. Serious aftermarket parts can turn the SVF3.9 into a powerful contender.


Tactical machine pistols are not a new concept and was no better represented in the early days by the Tanio Koba USP, which sported a long magazine and all sorts of flash hider and silencer add-ons to make the resulting package look more like a mini-machine gun. Working with newer generation technology, KSC later released the select fire Beretta 93R with integrated folding front stock. While these were a huge hit in the late 90s, WAs release of the Hi-Cap series gradually drew consumer interest into big powerful handguns that offered solid blowback and minimal (if not non-existent) gas cool-down.

Following in the recent revival of full-auto pistols spawned by the release of the KSC Glock 18C in early 2001, WA has seen its eyes water as sales of KSC airsoft pistols soared to unprecedented levels. With full-auto gas blowbacks making a comeback from the days of the KSC 93R and WAs own M11, most airsoft manufacturers are working hard to get their own versions of full-auto gas-blowbacks on the market.

A host of accessories can be added Many have even begun adapting their successful designs in gas pistols to sub-machine guns, case in point being the KSC M11A1 which is based on the same design as their own successful Glock 18C. As of this writing, Maruzen is working towards the final design of its full-auto gas blowback MP5K.

With the popularity of WAs own Hi-Cap Infinity SV pistols, it was the natural move for WA to design a full auto version of this popular line. Dubbed the Infinity Mk-II SVF3.9, WAs latest release is essentially a converted Infinity Hi-cap with a 2-piece slide. At first glance, the Mk-II SVF3.9 looks just like any other hi-cap series pistol but closer inspection yields some significant differences.

Overall weight is on par with regular SVs though the slide is significantly lighter than normal, likely catering for the high cycle speeds it is required to travel in full-auto mode. The most notable trait of this gun is the well crafted two-piece slide, which is shaped in such a way that the top portion is flat as opposed to being rounded like many other SV models. The rear portion of the slide functions like a regular pistol and cycles on each round. The front portion of the slide remains stationary during firing and anchors the metal inner and outer barrel in place. This front portion is secured to the lower frame by way of 2 hex screws. Observant readers will already have noticed by now that the SVF3.9 is likely a misnomer since only the rear portion of the slide measures 3.9".

Metal parts are abundant and include the lower frame, fixed muzzle block (front slide section), outer barrel and threaded barrel tip, slide lock lever, magazine release button, magazine, safety, recoil spring guide, front and rear sights, hammer, rear grip tang, firing selector switch. The extensive use of metal gives high rigidity and balance to the gun.

In all fairness, the entire footprint of the pistol is equivalent to a full 5" Infinity and the lower frame on the SVF3.9" is every bit as long at the 5" model. As of this writing, WA is scheduling to release another version of this pistol dubbed the SVF5, which will mean that the overall footprint will likely be equivalent to the standard Infinity 6".

Deceptive naming aside, the shorter and hence lighter slide allows it to cycle very quickly to give the SVF3.9 a fairly high rate of fire. However we felt the slide was a little too light, probably due to the limited use of metallic compound and heavy ABS plastic. As such, pulling the slide back when cycling the first round is not as gratifying an experience since the tensioning of the recoil springs sometimes resonate in the light plastic slide as you pull it back. The recoil spring is also lighter to offer less resistance in the blowback process. A lighter slide also means less backward momentum during cycling, which translates into less blowback kick.

The front and rear sights are made of metal and are both located on the rear moving slide, though they are non-adjustable. They are marked with white sighting dots for easy aiming in dim lighting.

One innovation that WA has developed for the SVF3.9 is a fully adjustable hop-up that does not require disassembling the gun for tuning. The design incorporates a small hole in the upper roof of the trigger guard, which tunnels upwards directly onto the hop-up screw. A hex-wrench is provided that allows you to access that hop-up adjuster by simply inserting the hex-wrench into this little access hole. We applaud WA for this new design since tuning hop-up in the past has always been a laborious cycle of assembling and disassembling pistols on every minor tweak, making "perfect" adjustments elusive.

The other mechanical functions of the gun are identical to any other handgun, except for the tell-tale select fire lever on the right hand side of the grip. It is located in the same position on the right side as the safety lever is on the left side, and offers two positions. When pushed downward, the gun operates in semi-auto mode. Pushing the lever upwards puts the SVF into full-auto mode. We found this metal lever quite difficult to operate given its relatively small thumbprint area, and it proved impossible to toggle without breaking out of your firing grip.

Threaded barrel allows attachment of 14mm silencer
Threaded metal barrel is standard equipment
External access to hop-up adjuster a "huge plus"!

For right handers, selecting full-auto mode required the use of the other hand to flip the switch upwards while keeping our firing hand in ready position. Selecting semi-auto mode was a little easier and required us to simply use the thumb from our firing hand to push the lever downwards. Of course, left-hand shooters will find operating this lever as easy as it is for most right-handers to operate the safety. In repeated testing, the select fire switch operated reliability and never once failed to put the SVF into the desired firing mode. We simply wished the lever offered more travel to make the selection process more assertive, and visual confirmation easier.

Most Colt frame pistols including the entire WA Infinity Hi-cap series offer two safeties, one being the safety lever on the side of the gun, and the other being the grip safety (below the grip tang) that is deactivated once you wrap the palm of your firing hand around the grip. The SVF breaks this rule and only offers the safety lever, and eliminates the grip safety. We do not understand why WA chose to eliminate this feature but we suspect it may be related to the additional complexity of building in the full-auto mechanism that leaves little room for the grip safety feature. In any case, the regular safety lever works fine and can be engaged upwards when the hammer is cocked. No safety is available for when the hammer is un-cocked but that is of little concern given that the SVF3.9, like all other Hi-cap series pistols, are single action.

Another prominent feature of the SVF3.9 is the tastefully sculpted rail frame that can accommodate the same accessories as the Glock 18C, including front grips and a wide array of flashlights and lasers. As show in the photo, we easily slipped on the SureFire flashlight onto the lower rail. But for many who crave to build the ultimate machine pistol, one rail is simply not enough, which is why WA has also released an aftermarket option to replace the stationary front slide with a tactical muzzle mount block that offers rails on the left, right and top sides of the slide. Together with the rail frame on the bottom, that leaves owners to attach accessories on all four sides for maximum flexibility. One configuration that WA is heavily advertising shows an optical sight mounted on the top, with a flashlight and laser mounted on either side. An RIS style front grip is mounted on the lower rail to give maximum tactical effect. The optional slide module is constructed entirely of black anodised metal and even comes with a silver metal outer barrel, which replaces the stock black metal barrel. All required screws and hex-wrenches are included. The threaded front tip of the outer barrel (the part that protrudes forward of the front stationary slide) remains unchanged though. The threaded barrel is a clockwise 14mm configuration and will take any standard 14mm clockwise threaded silencer or flash-hider.

WA is also in the works with releasing a high capacity extended magazine much like the one offered for KSCs Glock 18C, offering 50 rounds of constant firepower. Metal slides are also in the works to offer more heft, though prospective buyers should be warned that installing heavier slides will inevitably slow slide movement and hence rate of fire.

Field stripping the SVF requires a little more patience than the regular Hi-caps, and cannot be accomplished without any tools. You must first remove the front stationary slide section by unscrewing the two hex bolts on the lower frame (the slide is actually bolted to the lower frame). The slide can then be removed by pulling it forward and off the lower frame. The rear slide disassembles much like that on standard Colt Government frame models and is achieved through removing the slide lock catch. The complexity of field-stripping is probably the reason why WA decided the engineer the external access method for tuning hop-up. An interesting note is that the slide lock lever is extremely well sculpted and extends backwards much further than on regular SV pistols to allow easy access to your thumb.

On the field, the SVF performed quite well with both HFC134a gas, and the more powerful HFC22 gas. The power and cycle times achieved through HFC22 was visibly higher, though the internal design of the SVFs blowback cylinders and O-rings means that prolonged use of HFC22 will not help durability. As such, this is the only pistol in the entire WA Hi-cap line where we recommend upgrading with high-performance parts before running on long periods of time with the powerful HFC22 propellant. Loading the BBs into the magazine was quite easy and used the same stacked pour-in method that are common to all SVs. Interestingly enough, we noted that the tip of the BB feeder within the magazine (otherwise known as the magazine floor-plate) on our model was blue in color. Blue magazine floor-plates in the real-steel world are used to denote training magazines. Here, it allows you to differentiate between a magazine designed for the standard single shot Infinity's and this one designed for the full-auto versions. Note however that we were able to use standard Hicap magazines with the SVF with no problem.

In semi-auto mode, the SVF shoots like any other Infinity pistol, albeit with less recoil and noise. As mentioned earlier, more convenient tuning of the hop-up adjuster meant we were able to better maximize the range of our shots. Using HFC134a for our tests, we achieved effective kill ranges of approximately 60 feet, with accuracy gradually tapering off after 45 feet. Accuracy was fairly standard at +/- 3mm at 8 feet, and +/- 10mm at 20 feet. Power was clocked between 0.5 and 0.6 Joules on a 30 degree (centigrade) day with 0.2g BBs using HFC134a. Our tester was able to empty the entire magazine of 30 rounds in full auto with minor cool-down effects showing on the last 4 - 5 rounds. Rate of fire was impressively high, and while it was not possible for us to measure the exact rate of fire, our tester felt that the rate was comparable to the KSC Glock 18C. With limited blowback kick, it was quite easy to maintain course as we rained our "bullet hose" onto our target with limited dispersion.

Using HFC22 for our semi-auto tests demonstrated noticeably stronger kick and power at close to 0.9 joules of barrel exit energy. Interestingly enough, we found that the SVF behaved slightly better with HFC22 when using Hicap magazines designed for standard single shot versions.

Firing selector switch on right of gun (see 2 positions)
SVF3.9's 2 piece slide is a beautiful piece
Blue magazine floor-plate and sculpted slide lock lever

Overall, the SVF 3.9 is a joy to shoot, and for avid fans of the Infinity SV series, this is a dream come true. The flexible tactical slide module also offers endless customization opportunities that allow you to build a menacingly "maxed-out" machine pistol. While our expectations for the SVF3.9 may have been hyped up by hopes that the a full-auto version of a hi-cap pistol would offer as much kick and noise as the standard hi-caps, we must admit that the SVF3.9 exhibits a more subdued behavior compared to its standard siblings.

As a comparison, the KSC Glock 18C exhibited good kick and comparably high cycle times with good and reliable management of HFC22 propellant gas. (Our long-term tests have indicated that the 18C is engineered for HFC22 from the start and operates durably under long term use). The slightly heavier slide on the Glock 18C contributed to a better overall shooting experience, while a larger aftermarket of upgrade parts at the time of this writing makes the 18C more desirable for serious airsofters. Of course, WA or other manufacturers could easily turn the tables by releasing a slew of upgrade parts. But then of course, we are comparing two pistols built for different purposes; the 18C has a compact design for "daily carry" while the SVF3.9 is a purpose-built machine pistol.

Aftermarket muzzle mount block option for 3 added rails Selecting between semi-auto and full-auto on the Glock 18C is also easier since the selector is conveniently located on the left side of the frame for easy thumb operation (convenient, that is, for right hand shooters).

Obviously the two pistols have set out to conquer different markets, with the 18C appealing to standard hand-gun enthusiasts who value concealability and simplicity in handsome Glock styling. The SVF 3.9 is much more of a tactical offering whose fancy and more racy design serves as a perfect platform for building a true machine pistol loaded with accessories. Both are winners in their own right.

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