Piston-Packing 5.56s: Kel-Tec, Sig Sauer, and Ruger Redux

There's no doubt about it; the AR-15 has gone mainstream. Over the last several years, the growth in demand for black rifles has lured many manufacturers (including the big guys) to introduce their own versions of the venerable Eugene Stoner direct-gas-impingement design. Now that the market has matured, we are now seeing engineering departments introduce versions that are claimed to

Ain’t they pretty? These lovely ladies are, from left to right, the Sig Sauer 556 Classic SWAT No. SIG556302, $2399; the Kel-Tec SU-16 CA, $890 as tested; and the Ruger SR-556FB, $1995, which was also tested in the January 2010 issue. One of the more interesting things we looked at in this test was how these gas-piston guns heated up compared to a regular impingement design (see table opposite). We didn’t find a big difference in the heating temperatures after 30 rounds, except in the bolt temperature of the impingement gun. Even so, it wasn’t a crazy big amount.

In January, we compared a new piston gun, the Ruger SR-556, to two direct-gas-impingement units, rating the Ruger an A- in the process. This time, we put the Ruger SR-556FB, $1995, apples-to-apples against two more gas-piston models, the Kel-Tec SU-16…