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SP-8 Adjustable Stock
By Bill Mills - Photos by Dawn Mills - May 2006

When Smart Parts released the SP-8, they didn’t ignore it in terms of accessories.  Available at the time of its release was the optional SP-8 Adjustable Stock.

The stock converts the SP-8 from a compact carbine configuration to the feel of a rifle, with the option of adjusting into a more compact size for higher mobility.  Aside from a Smart Parts logo embossed near the butt, the stock looks nearly indistinguishable from the collapsible stock of H&K’s XM-8 prototype battle rifle.  The adjustable stock also adds a rear metal attachment point for a sling.

Installation of the stock onto an SP-8 for review was a very simple process.  First the stock butt-cap was removed from the SP-8.  A quick-strip pin holds the butt-cap in place, and finger pressure or pulling was not enough to remove it.  Instead, pressure from a 1/8-inch hex wrench easily pushed it out.

With the pin out, the butt-cap slid easily off of the rear of the SP-8’s upper receiver.  The stock slid into it position just as easily.  Getting the pin in place to secure the stock turned out to be a little more complex.  On close inspection there was a slight amount of play between the stock and the receiver.  

Putting a little pressure on the stock – pushing it up against the back of the upper receiver, brought the holes for the pin into perfect alignment and it slid into place.  This proved easiest to do by simply shouldering the SP-8, as if about to fire, and pulling it back into the shoulder.  Once locked by the pin the stock no longer had play and was set firmly in place.

After getting the hang of the procedure, a swap from the butt-cap to the stock took about ten seconds to accomplish – another five seconds if done without a tool, simply pressing and pulling the pin out with fingernails.  The pin remained securely in place through normal use and movement and even more outrageous shaking and knocking about in an attempt to “accidentally” dislodge it.

While collapsed, the stock adds approximately five inches of total length to the SP-8.  Extended, this increases to eight inches.  On the inside face of the butt is a small release that unlocks the stock, allowing it to slide in or out to any of seven locking positions.  In testing the middle positions seemed unnecessary, with the fully collapsed position being easily mobile, and the fully extended position comfortable for a shouldered shooting stance aiming with an ADCO Square Shooter Sight.

In place, regardless of position, the stock did prevent compressed air, or CO2 tanks ranging from 7 to 20 ounces from fitting into the SP-8’s ASA.  This left two straightforward alternatives – fitting the SP-8 with a drop forward to lower the tanks out of the stock’s way, or to use a remote.  For testing an ACI coiled remote was used, allowing the SP-8 a more rifle like balance.

With the stock extended the SP-8 felt more natural to shoulder than it had previously with the butt-cap and a 68 cubic inch Crossfire compressed air system in the bottom-line.  Rather than an arm wrapped around a tank, the stock fit nicely to the shoulder, and provided stability.  The downward curve on the top of the stock provided enough room to use the red-dot sight easily without mask interference.  

With the stability of a proper stock, and position that allowed use of a sight, tight groupings that were on target from the first shot were easy to achieve.  The SP-8 Adjustable stock quickly converts the SP-8 from compact carbine into a paintgun ready to go from the woods, into door to door action on a MOUT field.