Hardware: TenPoint Viper S400

posted on August 25, 2020

Every year, after testing dozens of guns, bows and gear, I develop a “best gear list”—and before I get in to the guts of this review, I can tell you that TenPoint’s Viper S400 crossbow is among the best crossbows ever tested in terms of value, features and performance.

TenPoint Viper S400 Side View

In essence, the Viper S400 is a compound crossbow with an ultra-small footprint, plenty of speed, outstanding accuracy and all the features that make it safe and easy to shoot. Certainly $1,500 isn’t cheap by any means, but when compared to crossbows with similar features and performance that cost $1,000 more, the S400’s upper-mid price point seems more palatable. But let's start with the Viper’s main feature, it’s ACUslide cocking and decocking mechanism. I call it a bullpup after the style of compact guns owning a design that places their actions behind their trigger and grip. This lends the bow a long, 11-inch powerstroke yet keeps the bow’s overall length to only 32 inches.

Where before TenPoint’s solution to easy drawing was its excellent ACUdraw system that utilizes an external winch system to harness the string and pull it back until it engages the fire-control and cocking system, the ACUslide is akin to the system of crossbow rival Ravin, wherein the entire fire-control mechanism/trigger box slides—sled-like via captured rollers—to engage the string before being winched back into position where it engages the trigger linkage. The ACUslide has many advantages over the older winch systems. In sum, this apparatus—and indeed the entire bow as a whole—represents a tremendous feat of engineering. As a quick example of its design engineering, look no further than the Viper’s crank handle.

When removed from its cubby in the underside of the stock where it remains for safe keeping, the winch handle extends to deliver almost double the leverage so that it requires less force to turn. As such, anyone can cook this bow.

TenPoint Viper S400 Safety and ACUslide Cocking System

Secondly, the internal winch device was made so it can not only cock the bow via a continuous anti-reverse winch system that’s also quiet (hugely important in the deer woods), but it can be decocked just as safely and quietly.  Whereas in the past, a crank mechanism that was used to decock the bow could slip from the shooter’s grasp and crack the knuckles or worse, the Viper’s crank handle can be vacated at any point—even during the peak of the powerstroke—and it will safely hold the string where it is. This is a huge deal.

Thirdly, like a Swiss Army knife, the handle contains a metal pin that can be used if ever the user short-cocks the bow—a common problem with nearly all crossbows—wherein the anti-dryfire device is engaged but the string is not fully cocked, thereby rendering most crossbows incapable of firing and not easily decocked. In the Viper’s case, since the trigger box can be let down at any time via the forward assist knob and the crank, the problem that can result is the string latch cannot be removed from the string even when the bow is uncocked. So this tool can be used to disengage the string latch. It sounds complicated, but it’s actually very ingenious and remedies a common problem with crossbows that I’ve often called “the dreaded purgatory position.”

The Viper’s fire-control system/trigger box itself is very well made. Its automatic safety is ambidextrous, and its trigger is one of the best I’ve ever experienced on a crossbow, with a measured pull weight of 3.5 pounds. This is a tough engineering feat considering the massive holding weight required of the sear; it’s taken crossbow companies years to perfect crossbow triggers. TenPoint’s is one of the best, and its trigger is vitally important for accuracy, considering a crossbow’s turtle-like lock time (compared to a firearm) that makes follow through and a perfect trigger squeeze so important.

Moving forward, the Viper S400 has all the meaningful safety devices, including finger wings and a hold-through fore-end, which promote safe hand and finger placement while shooting. Its aluminum barrel has what TenPoint calls “Micro Trac” technology that reduces the amount of contact between the bolt and barrel, thereby reducing friction and in theory improving speed and accuracy. But the real technology here is Viper’s eccentrics. Although a couple years old now, its Quad Four cam system is worth rehashing because this compact, powerful block-and-tackle system places the string’s powerstroke in line with the cam channels so no torque is placed on the cams or the string as they travel. All of these things add up to stunning accuracy.

TenPoint Viper S400 Crossbow Top View

The Viper’s other best trait is borne from its compact limb-and-cam system that allows it a ridiculously narrow 7.2-inch axle-to-axle length (10.5 inches cam-edge to cam-edge.) This cocked width is what makes it such a joy to carry and hunt with the Viper. It’s nearly a third narrower than crossbows of old, and this cannot be overstressed for a hunting crossbow.

As a whole, the 9-pound (as you’d shoot it) Viper S400 is just really well made. Its parts are made from quality components and are personally assembled in Ohio. I can tell you this because its included scope only needed to be bolted on to the Picatinny rail and fine-tuned—proving someone tested it at the factory. (The Chinese-made, ballistic reticle scope itself is no great thing of optical beauty, but it does get the job done.) At any rate, when a crossbow is solidly made, it tends to be quiet and hold up after many shots. The Viper imbues a sense of confidence you can feel as soon as you lift it. Then you shoot it … .

At the range, the 448-grain EVO-X arrows/field tips provided with the bow produced velocities of 365 fps for 132.5 ft.-lbs. Kinetic energy—plenty for any big-game animal. Lighter arrows are available that produce 400 fps. Personally, however, I like the heavier arrows that tend to be more accurate, deeper penetrating and quieter in most crossbows.

Accuracy-wise, at 30 yards on a windy day, it consistently destroyed arrows! My second and third shot produced a Robin Hood, then my next three-shot group destroyed another nock! I recorded a stellar .77-inch group average at 30 yards, but I truly believe the Viper is a .50-inch (30-yard) bow in perfect conditions, and that is about as good as crossbows can get due to the thickness of the arrow shafts and fletchings. This crossbow is more accurate than most slug guns.

As you can tell, I’m a fan of the Viper and believe it may be the best I’ve ever tested. The Viper S400 is safe, easy to draw and even de-cock, quiet, compact, plenty powerful and ridiculously accurate. Though I realize it isn’t cheap, if you are a serious crossbow hunter, I’d think seriously about ponying up the cashola for this crossbow.

Technical Specifications
• Velocity: 390 fps (advertised w/400-gr. bolt)
• Trigger: 3.5 lb. pull weight
• Dimensions: length 32" (w/o foot stirrup); axle-to-axle width 11" (uncocked); power stroke 11"; weight 7.5 lbs. (w/o accessories)
• Finish: Veil Alpine (pictured); graphite
• Accessories: 3 arrows, quiver, scope, field points, string lube
• MSRP: $1,549.99-$1,649.99; tenpointcrossbows.com


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