From the end of its steel buttplate to the tip of its hooded front sight,
the HK SL6/7 carbine is more than slightly reminiscent of the famous
World War 11 German semiautomatic G43 rifle. But the similarity is
only superficial. The G43 was gas-operated with a gas cylinder above
the barrel in the same manner as the Russian Tokarev M38/40 rifles
and locking was by means of hinged flaps set in recesses on each side
of the receiver in imitation of the Soviet Degtyarev light machine gun.
The HK SL6/7 carbines are different. They use the delayed-blowback,
roller-locking system of operation - a hallmark feature of Heckler &
Koch's entire line of small artns. HK bolt mechanisms consist of two
major components: a bolt head and bolt carrier. Although referred
to as "locking-roller," the action is never completely locked. In the
battery position, inclined surfaces on the bolt carrier lie between the
two rollers on the bolt head and force these rollers into recesses in
the barrel extension. After ignition, the rollers are cammed inward
against the bolt caffier's inclined
planes by rearward pressure on the
bolt head. The bolt carrier's rearward velocity is four times that of
the bolt head. After the bolt carrier has moved rearward four
millimeters, the rollers on the bolt head (which has moved only one
millimeter) are completely depressed, pressure has dropped to the
required levels of safety, and the two parts continue their backward
A long, pivoting ejector bar is mounted to the left side of the SL6/7
receiver and is spring-loaded.
The HK SL6/7 weapons are actually a carbine-length version of the
HK 630/770/940-series sporting rifles. "SL" presumably stands for
Self-Loading (Selbstlade). The numbers "6" and "7" are rough
approximations, in millimeters, of the overall cartridge length the
action will accept. The SL6 is chambered for the 5.56mm NATO
(.223 Rem.) cartridge. SOF's test rifle is an SL7, which is chambered
for my favorite GPMG and sniping-rifle round, the 7.62x51mm NATO
(.308 Win.) cartridge.
Compact and rugged, these slick little carbines lend themselves to
applications beyond their intended roles as hunting/sporting pieces.
Both the SL6 and SL7 weigh in at 8.36 pounds, empty. Their stubby
17.71-inch barrels are somewhat thicker than those of the HK
630/770/940 series. Four-groove barrels feature the hammer-forged
polygonal rifling that characterizes Heckler & Koch firearms. The
right-hand twist has one tum in 10.6 inches for the 5.56mm chambering
and one tum in 11.0 inches on the SL7's 7.62x51mm NATO barrel. The
upper and lower receivers are machined from solid bar stock.
The chambers are fluted on all Heckler & Koch and CETME
delayed-blowback, roller-locking firearms. The 12 longitudinal flutes
extend rearward from the baffel lead to 0.25-inch from the chamber
face. These flutes reduce the cartridge case's bearing surface and
permit propellent gases to flow around the case acting as a lubricant
to ease extraction. As delayed blowback does not offer the available
power reserve of gas operation under adverse conditions and there
is no primary extraction, chamber fluting is required for reliable
functioning. Ejected cases are all marked with distinctive striations
but, contrary to popular belief, this does not affect their potential
The barrels and other exterior metal parts are finished matte black.
The chamber area of my specimen has a plum-colored tone often seen
on Gennan WWII small arms manufactured late in the war. Although
nostalgic, this finish usually signifies a hasty finishing procedure,
because this color results from dipping high-nickel steel into salt-bluing
solutions at improper temperatures (too low) for an insufficient period
The nicely figured, uncheckered walnut stock also carries a WWII
flavor in both its dull, oiled finish and configuration. The upper forearm
is walnut as well and ventilated by three longitudinal 1.5-inch grooves
cut into either side. The smooth wrap-around steel buttplate is retained
by two large wood screws. There is no butt-trap storage compartment.
A prototype green-plastic stock and forearm have been developed and
will be available by mid-1985.
The front barrel band is held in place by two spfing-loaded pins of the
type used on the forearms and buttstocks of all HK military small arms.
These pins can be inserted from either side and I have been involved in
numerous discussions as to which direction is the coffect placement.
Some maintain that it is more natural for right-handed shooters to insert
them from the right side of the weapon. Some insist they should be
alternated. In El Salvador, troops armed with the G3 rifle insert the
pins from the left side so they cannot be inadvertently pushed out
when jarred against the body or combat webbing.
A fixed-fing front sling swivel is attached to the barrel band. The rear
swivel is inlet into the left side of the buttstock in the European style
and accepts either the web or leather HK military slings.
Cut into the stock just forward of the trigger housing is the magazine
well. The staggered-row, detachable box-type magazines are of
all-steel construction from the HK 630/770 series. It often takes more
than a little swearing to disassemble them. Issue magazines hold four
rounds in the SL6 and three rounds in the SL7, and fit flush into the
stock's well. The SL7 magazine is marked ".243" and ".308," although
to date the former chambering is not offered in this series. An optional
10-round magazine is available for either (the 10th round enters only
with a great deal of pushing). They insert easily - but only when the
bolt is retracted - and fall away freely when dropped by the magazine
catch release located in the front portion of the plastic trigger guard.
Either we're all becoming more jaded or the plastic wizards are getting
better at simulating metal. The polycarbonate trigger guard looks good.
Two 5mm hex-head screws hold the trigger housing to the action. A
screwdriver for removing them and the upper receiver's retaining screw
The drag-free, single-stage trigger breaks crisply and consistently at
five pounds on my test sample. Amazing, you say? Well, this isn't your
everyday G3 trigger mechanism designed to withstand a 25-meter drop
test. Although the hammer is still driven by two coil springs, the auto
sear has been eliminated and a spring plunger bears on the sear to
yield positive engagement.
The safety lever is located on the left side of the stock, forward of the
trigger guard. It cannot be reached or manipulated by the firing hand.
Its spindle locks the hammer in the cocked position and it cannot be
activated if the hammer has been rotated forward. To place on the safe
position the lever must be moved downward until a white dot is exposed.
When the safety lever is rotated counterclockwise to its upper position,
the white dot is covered and a red dot becomes visible to indicate the
The folding retracting handle moves in a slot cut into the right side of
the lower receiver. This is the reverse of the Heckler & Koch military
small arms in which the retracting lever moves in a slot cut into the left
side of a tubular extension welded to the receiver that also contains the
bolt carrier's forward extension. Considerable force is required to draw
the SL6/7 cocking lever rearward. A catch lever, located directly behind
the cocking lever, holds the bolt group in the open position and must be
depressed to release the bolt group and chamber a round. When charging
the weapon, the retracting handle must be allowed to move forward
without restriction. The bolt does not stay open after the last cartridge
in the magazine has been fired.
The front sight is a stamped-sheet-metal disk with a rectangular post
that fits into a slot in the protective hood and is held in place by a roll
pin. The entire front-sight assembly has been sweated onto the barrel's
The rear sight is the standard rotary drum found on all HK military
weapons. Criticized by some, it is nevertheless a sturdy affair. There
are four elevation settings and the drum can be tumed in either direction.
The unmarked, 100-meter position is an open V-notch. The 200-, 300- and
400-meter positions are peep apertures, 0.062-inch in diameter. The sights
are factory-zeroed for NATO standard ammunition. Use of lighter or heavier
projectiles will require recalibration. Elevation zero is altered by insertion
of a special tool with catch bolts into the rear-sight cylinder to mate with
the cylinder's two splines. The sight cylinder is then rotated in the desired
direction. This tool also contains a Phillips-head screwdriver used to loosen
the lock screw and turn the windage-adjusting screw. Anyone wanting to
shoot at longer ranges can replace the rear-sight assembly with the
1,200-meter rear sight used on the HK 21A1 machine gun - Why anyone
would want to do this I don't know. A more sensible alteration is the
knurled windage-adjustment knob offered by A.R.M.S. (Dept. SOF, 230
West Center Street, West Bridgewater, MA 02379). This knob replaces
the Phillips-head windage-adjusting screw and can be installed in less
than a minute. It perrnits instant horizontal-sight adjustment without a
Two rectangular recesses have been cut into the upper receiver to accept
the HK 05 claw-type scope mount. Either 30mm rings for European scopes
or 25mm rings for the standard one-inch U.S. scope tubes are available.
A large vertical lever is used to compress the mount's clamps for quickly
attaching or removing the mount from the rifle. While it's unorthodox in
appearance, the HK 05 mount is stable and rigid. Repeated removal and
re-attachment failed to affect the scope's zero. A 3mm hex wrench
is provided to secure a scope to the rings.
A Swarovski ZFM 6x42mm military scope was used for SOF's test and
evaluation of the SL7. This superb piece of rugged optics is available
with either a plain one-inch steel tube or an aluminum tube with a NATO
STANAG 2324 mount. The field of view is four degrees, or seven meters
at 100 meters. Luminosity and resolution are outstanding - almost Starlight
capability on a really bright night.
After initial zero adjustments, changes in elevation, from 100 to 800 meters,
are made by extemal adjustment knobs calibrated for the trajectory of
the 7.62x51mm NATO military cartridge. The windage-adjustment unit
is located on the right side of the scope. Each calibration mark moves
the point of impact one meter at 100 meters range. The reticle pattern
consists of standard crosshairs in the center with thick bars at the outer
perimeter. A luminescent tritium reticle will soon be available. The reticle
is noncentered, i.e., as the range drum is set for longer distances, the
crosshairs move toward the bottom of the field of view. While somewhat
distracting at first, it does instantly alert the shooter to his range setting.
The scope is set for parallax-free viewing at 300 meters but can be
changed by turning the ocular. The ocular has thoughtfully been
fitted with a rubber rim to protect those who tend to "crawl" the scope.
However, no scope caps are provided - an irritating omission on such
high-quality optics. Six-power magnification offers the best compromise
for most sniping applications. This level of milspec quality is not cheaply
acquired. The ZFM 6x42mm scope carries a suggested retail price of $535.
Technical brochures can be obtained from Swarovski America Ltd. (Dept.
SOF, One Kennedy Drive, Cranston. RI 02920).
The SL6/7 cannot be disassembled without the aid of a 5mm hex wrench,
also included. Remove the scope and magazine. Clear the weapon. Loosen
the 5mm allen screw at the rear of the upper receiver - a somewhat tedious
process if you take pains not to mar the stock. The recoil spring butts
against the upper receiver and tension never slacks off on the screw until
the very end of the ordeal. Lift up and back and remove the upper receiver.
Remove the retaining screw. Withdraw the double-coil recoil spring and
guide rod which run in a hole in the bolt carrier, strangely offset to the left.
Lift out the rubber buffer and its sheet-metal retaining clip (not on the SL6),
located at the end of the lower reciver. Retract the cocking lever. Insert
the long end of the hex wrench through the retaining-screw hole in the
lower receiver and compress the firing pin while lifting the bolt assembly up
Stripping and reassembling a roller-locked HK bolt assembly can be
frustrating the first time around. Rotate the bolt head clockwise one
quarter turn and withdraw it from the so-called locking piece. Continue
to rotate the locking piece and it will release from the bolt carrier along
with the firing pin and spring. That's the easy part.
To reassemble the bolt group, proceed exactly in this manner. Slide the
spring onto the firing pin and insert both into the bolt carrier. With its
locking lug positioned upper dead-center, press the locking piece against
the firing-pin spring as far as it will go and rotate counterclockwise one
quarter turn. Place the beveled surface of the bolt head directly under
the spring-loaded bolt-head locking lever on the bolt carrier (to do
this you will have to rotate the locking piece again, ever-so-slightly
counterclockwise). Slap the bolt head smartly with the palm of your
hand to drive it under the locking lever. Make certain you have about
3mm of clearance between the bolt head and carrier. Rotate the bolt
head counterclockwise about one half tum, until the locking rollers are
at the same level as the bolt carrier's camways. Then pull the bolt head
away from the carrier as far as it will go, so the rollers can recess
completely into the bolt head.
The forearm can be removed by driving out the baffel-band pins and
sliding the barrel band toward the muzzle. The 5mm hex wrench can be
used to remove the trigger guard for disassembly of the trigger mechanism.
I recommend this only for trained armorers, unless you desire to send
the rifle back to HK in a paper bag along, with an embarrassed, tear-stained
While there is no gas system to clean, delayed-blowback firearms become
quite fouled in the area of the barrel extension immediately to the rear
of the chamber face. Although difficult to reach, it should be swabbed
thoroughly until clean.
Reassembly is generally in the reverse order. When inserting the bolt
assembly back into the lower reciver, first place the bolt-head ejector
camway onto the ejector, then push in the locking rollers and firing pin,
press the assembly downward from the rear and slide it forward to the
battery position. Reinsert the buffer and recoil-spring groups. Thread
the retaining screw one full turn into the lower receiver. Slide on the
upper receiver until its retaining slot is seated on the screw's collar.
Tighten the screw firmly.
After reassembly, the headspace should be checked. This is measured
by the gap between the bolt head and bolt carrier when the bolt group
is in battery. The permissible tolerance is 0.005 inches to 0.020 inches.
The preferred headspace gap is 0.008 inches to 0.017 inches.
One thousand rounds of military-type ammunition was selected for the
test and evaluation. Two hundred fifty rounds of each of the following
were fired through the SL7 fitted with the Swarovski ZFM 6x42mm scope:
G.I. ball - Vietnam era - carrying a WRA '66 headstamp (Winchester
Repeating Arms, 1966), PMC (also M80 configuration), FMJ match reloads
(with a 175-grain, lead-cored, boattail projectile powered by 41.5 grains
of Winchester Western 748 flattened-ball propellent) and West German
surplus with a headstamp marked IWK 19-65 with the NATO cross in
The West German ammunition was manufactured by Industrie Werke
Karlsruhe (formerly DWM) in 1965. It is packaged in 20-round boxes,
which, in turn, are packed in sealed 200-round green plastic "battle
paks." It is Berdan primed, but not corrosive, The lead-cored, boattail
projectile weighs 145 grains. The propellant is a round-ball type with
a nominal charge weight of 44 grains. This ammunition has been readily
available to U.S. shooters for several years.
When chronographed, it exhibited the lowest standard deviation (22 fps)
of all the ammunition used in the test. Not surprising, then, that it also
produced the greatest accuracy. Under conditions of 15mph gusting
winds, the IWK 19-65 shot a startling 1.0 MOA. Even though the SL7's
barrel is floated in the stock, such performance through a semiautomatic
carbine with a less than 18-inch barrel is an outstanding testimony to
the rifle/scope/ammunition combination - a German rifle and ammo with
an Austrian scope.
This was followed by the FMJ match reloads which shot 1.7 MOA. Both
the PMC and WRA ammunition fell far short of this level. A mean figure
of 2,700 fps is the standard NATO muzzle velocity for M80 ball ammunition.
The SL7's short barrel lost only 125 to 250 fps in velocity.
There were no malfunctions except for two "bolt-over-base" stoppages
induced when the weapon was purposely held away from the shoulder
to permit the weapon to recoil rearward along with the bolt group.
Roller-locked, delayed-blowback rifles must be held securely against
the shoulder so the bolt can move sharply rearward in relation to the
relatively fixed mass of the receiver body or the bolt group may not
complete its backward travel and the recoil spring will not compress
As it is a bit heavy for a so-called carbine, felt recoil is no more than a
gentle shove rearward (also a function of the delayed-blowback method
of operation). However, the handling characteristics and balance are
excellent and hit probability remains high. The ejection pattem is quite
forceful - about 10 to 15 feet out to the right.
Marketed as a hunting system, the SL6/7 series has a much broader
potential. When properly scoped, they offer a reasonably-priced,
medium-range sniping alternative to law-enforcement agencies. They
would constitute a valuable addition to any survivalist battery. Their
military applications remain limited by the magazine capacity and
awkward location of the safety.
I can find little to criticize in SL6/7. Its outstanding accuracy potential
in such a compact envelope are atuibutes which merit a close examination
of this modern-day G43 look-alike. The suggested retail price of the
SL6/7 carbine is $532.