Knights Armament SR-47 Page
New SR-47 merges designs
SCOTT GOURLEY, JDW Correspondent, California
US special operations forces have received a small number of new assault
rifles optimised for the type of cave-complex fighting experienced in
The weapons are based on the M-4/M-4A1 carbine variants of
the M-16 assault rifle family, but fire the 7.62 x 39mm Soviet-designed
cartridge and magazines used in the AK-47 assault rifle.
Armament Company of Vero Beach, Florida, delivered the first six rifles, called
the SR-47 (Stoner Rifle-47), to the US Special Operations Command (USSOCOM) in
January. The company received a contract for an initial six weapons in late
David Lutz, vice president of military marketing for
Knight's Armament Company, said: "For the last couple of years there was a
requirement in USSOCOM for an addition to their [M-4 series carbine] SOPMOD
[Special Operations Peculiar Modification] kit that they called a 'Special
Purpose Receiver' (SPR).
"Originally they called it the SPR V1 for
'variant one', and it was to be a drop-in 7.62 x 39mm receiver replacement."
According to Lutz, government laboratory efforts to satisfy the SPR
requirement were further complicated by "user input" from the USSOCOM specifying
that special forces did not want to use the "straight box" M-16 magazines but
instead wanted to utilize "battlefield pick-up" AK-47 magazines taken from
"That was a dilemma because the AK-47 magazine won't go well
in a straight chute dimensional magazine - it just won't happen," he said.
He added: "But actually this program was kind of on a back-burner
until US special operations guys were going into these complex of tunnels that
were so deep, expansive and target-rich that they couldn't take enough loaded
M-16 magazines. So they wanted a weapon that had all the muscle memory of an M-4
- safety, grip, everything that's familiar to the soldier or the SEAL - but
capable of using battlefield pick-up magazines."
Instead of a drop-in
receiver addition to the SOPMOD kit, design changes mandated a completely new
weapon with resulting change in terminology from Special-Purpose Receiver to
Special-Purpose Rifle (SPR).
"To enable the use of battlefield pick-up
magazines, we had to make the upper and lower receiver 0.25in longer. You
couldn't take an M-4 receiver and even machine it out to take the AK-47 magazine
because it was too short. That also meant that the bolt carrier had to be made
longer and the firing pin had to be made longer.
"So you started losing
what some people would have liked to have in terms of optimal interchangeability
of parts; that's just part of the trade-off to fire the different cartridges,"
He highlighted the advantages of the 7.62mm size round for
close-quarter battle (CQB) operations. Noting that many of the world's
counter-terrorist organizations have evolved from 9mm to 5.56mm ammunition over
the last decade, he highlighted the larger 7.62mm ammunition for the ability to
package heavier, slower bullets that could provide greater contributions in CQB
In addition to the extended upper and lower receivers,
another challenging design effort in the SR-47 involved getting the M-4/M-16
magazine catch to externally function like the M-16 magazine but work with a
curved AK-47 magazine. In practice, US soldiers use gravity to 'drop' their
empty M-16 magazines. The SR-47 design requires the introduction of an internal
magazine ejector to push the empty AK-47 magazine from the bottom of the weapon.
Additional design features include the introduction of a free-floated match
"This particular 7.62 x 39mm is probably the most accurate
7.62 x 39mm in the world because it's got a really fine free-floated barrel,"
"And, of course, it has the rail system so all of the other
SOPMOD accessories off the M-4s are compatible.
"There's also a
possibility, although they haven't let the contract yet, that there could be
another variant that we'd call the SR-74. That could be used if our special
operations guys go to a country that has the 'newer' 5.45mm former Soviet
weapons. Then they would also have the same ability to pick up magazines."
All six of the SR-47s were delivered with sound suppressors, which Lutz
described as "essential" in tunnel operations because of the weapon report.
"We don't know how the six did," he said. "We don't know if they are
ever going to order one more. We don't know if we're going to get the second
phase, which is to develop the 5.45mm version. But this is probably the hottest
weapon that's out there right now."
Lutz concluded: "The SR-47 is a
great gun because of the three technologies that it marries: the basic Stoner
gun design; the AK-47 series cartridge and magazine; and the modular weapon