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SP-8 Stealth Barrel Kit and Tactical Rails
By Bill Mills - Photos by Dawn Mills - June 2006

When Smart Parts released the SP-8, along with it came some SP-8 specific accessories, mirroring features found on the real-world XM-8.  These included the Adjustable Stock, Stealth Barrel Kit and accessory rails.

The standard SP-8 barrel is 14 inches long, and it sits within a foregrip that forms a 7-1/2 inch foregrip.  In contrast, the Stealth Barrel kit includes a 20 inch barrel, with a foregrip that extends 12-1/4 inches out past the upper receiver.  The SP-8’s standard configuration is analogous to the compact XM-8, while the Stealth Kit mimics the standard XM-8 dimensions.

There are more differences between the two barrels that just the length.  The most visible of these differences are the muzzles.  The stock barrel has open slots, which look like the compact XM-8 barrel, and conveniently have an end view which is not unlike the ring portion of the Smart Parts logo.  The Stealth Barrel, in contrast has a narrower neck, which flares out around its muzzle brake.  While a slotted design, the muzzle brake has four enclosed slots ending in a full ring muzzle.

Both barrels are ported, but due to the length difference the Stealth Barrel’s porting is spread over 6 inches, rather than 2.1.  Additionally, the Stealth Barrel’s porting holes are smaller than the stock barrels.  They are only 0.085 inches in diameter compared to 0.100.  Why the difference?  Sound.  Quieter operation was one of the design goals for the Stealth Barrel and how it got its name.  The Stealth Barrel’s ports are arranged in groups of two and three, which line up air spaces that are formed by the support rips inside its foregrip. 

The interior support walls of the Stealth Barrel foregrip are of a smaller diameter than those of the short foregrip, and the Stealth Barrel has a smooth polished outer finish, rather than bead-blasted, so that it can fit snugly into the foregrip.  The fit is so tight, in an effort to prevent air – and sound – from passing between the chambers, that the Stealth Barrel ships from the factory lubricated with grease to make installation and removal easier.

Installing the complete Stealth Barrel kit for review was little more time consuming than changing a barrel.  The stock barrel was unscrewed from the SP-8, and the foregrip’s lock pin pulled out.  The foregrip was slid out of place taking the stock barrel with it.  The Stealth Barrel came sitting inside of its foregrip, and the two parts were slid into place on the SP-8’s upper receiver.  The forefrip was locked in with its push-pin, and the barrel was screwed into the SP-8 receiver by twisting its muzzle.  Getting the foregrip installed the first time proved to be a little tricky.  The push-pin fits through a hole in the wrap-around rubber grip portion of the foregrip, and a slight mis-alignment of the hole in the rubber grip and the holes underneath made inserting the push pin difficult at first.  Trimming a tiny bit of rubber at the edge of the push-pin opening with a hobby knife made all the difference in the world for fast and easy barrel and foregrip changes.  All that remained was to re-adjust velocity at the chrono station.

In use, the extra length on the front of the SP-8 definitely changed its feel and balance from compact to full size.  While not as easy to tuck and pivot, the full length foregrip was more comfortable and natural to hold in a typical rifle shooting stance with the adjustable stock extended.  The feel changed from the typical hold a paintgun by the grip and vertical regulator (or in the SP-8’s case dummy magazine) to a traditional shooting stance, which helped the use of a red-dot sight feel more natural.

The big question for a barrel called Stealth was, “how quiet is it?”  To find out, the SP-8 was mounted on the WARPIG Ballistic Labs test stand and fired both with the stock barrel and foregrip, and with the Stealth Barrel and foregrip.  Peak sound level measurements were taken at a distance of 10 feet from the muzzle, approximately 45 degrees to the right of the barrel’s central axis. 

Over a series of ten shots, the SP-8 averaged 54.8 dB peak sound output.  Over ten shots under the same conditions, the SP-8 fitted with the Stealth Barrel Kit averaged 52.7 dB peak sound output.  While not huge, the Stealth Barrel Kit did produce a measurable sound reduction of just over 2 dB.  Not apparent from the sound level data was how the Stealth Barrel changed the quality of the sound.  With the Stealth Barrel Kit in place, the tone of the SP-8s report was altered.  While this observation was purely subjective, it seemed more difficult to locate by hearing alone.

The SP-8 ships equipped with a single Picatinny/Weaver compatible sight rail, but for many players into scenario and Milsim paintball much of the fun lies in all the cool gadgets they can put on their gun.  The SP-8’s accessory rail provides three more rails that will accept Picatinny or Weaver compatible components, and they can be attached to either the stock or Stealth foregrips.  All three rails are made of a durable black molded plastic.

The two side rails are 4.585 inches in length, and mount via included screws on either side of the foregrip.  The screws bite into screw holes that are pre-molded into the foregrip.  These side rails are positioned to accept accessories like flashlights, lasers, or even red-dot sights for players who prefer to sight along the side of the barrel. 

The third rail accessory rail has an angled base that compliments the curve on the bottom of the foregrip, making the rail parallel to the barrel.  Two screws are used to mount this rail, but because it is likely to see more stress than the side rails, these screws thread into metal inserts inside the foregrip.  The bottom-rail handle similar accessories, or RIS (Rail Integrated System) components like vertical grips or bipods.

For testing, we fitted an RIS vertical grip on the lower rail.  With the Stealth shroud it proved effective while shooting from the hip, but in a shouldered position the rubber grip built into the Stealth foregrip was still preferred.  With the standard barrel and shroud, and the butt-cap instead of a stock, however a vertical grip on the bottom accessory rail gave the SP-8 the compact feel of a PDW (personal defense system) configured weapons system.

Using a vertical grip on the center rail also proved very effective for shooting around corners while remaining behind cover.  Normally this is something that would be avoided, as blind firing (firing without seeing the target) is unsafe, however, we put together a feel and balance test configuration with a thermal sight from Exigence, Inc.  It’s swiveling digital eyepiece made it easy to see what was in the crosshairs from a shouldered, hip-shooting, or around the corner firing position – as well as spot people by their body heat regardless of camo or darkness.

The Accessory Rail Kit and Stealth Barrel Kit from Smart Parts integrated into the SP-8 without problem, and gave it more versatility in terms of configuration, while maintaining its Milsim form, mimicking the XM-8 Battle Rifle.
 

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