The P90 Personal Defense Weapon was originally designed
by Fabrique National Herstal SA of Belgium as a personal
defense weapon for troops whose primary mission is something
other than the use of small arms. Thus, the P90 is intended
for people such as vehicle drivers, operators of crew-served
weapons, support personnel and other troops who are often
issued sidearms or submachine guns. The goal was a select-fire
weapon of ultra-compact design that would provide superior
hit probability to the aforementioned weapons out to greater
distances thanks to the new compact 5.7x28mm round. These
characteristics, combined with the availability of SB193 subsonic,
L191 tracer and SS190 supersonic ammunition for the P90,
provide a very interesting package for Special Operations
as well as for law-enforcement, counter-terrorist, security
and executive-protection applications.
Many of these additional missions would depend upon - or be
enhanced by - the availability of a compact sound suppressor.
That suppressor would have to be capable of sustaining
substantial full-auto fire with standard duty ammunition (an
impossible dream until very recently), while providing enough
suppression with subsonic rounds to hide the fact that a shot
has been fired when the tactical situation demanded stealth.
FN Herstal SA asked Gemtech to develop a military quality
suppressor for the P90 that would be compact, tolerate
full-auto fire, and incorporate a snap-on quick mount which
would retain the FN muzzle brake or at least incorporate that
design into a replacement fixture.
Gemtech's design team of Dr. Phil Dater, Greg Latka, and
Jim Ryan devoted a great deal of time and energy into the
project over the course of a year. Their impressive M4-96D
suppressor for the M4A1 carbine - which Gemtech initially
developed for the Naval Surface Warfare Center - was
already in production, and this became the inspiration for
the new SP90 suppressor. The process of adapting the
M4-96D technology was more complex than one might guess.
Some qualities of the new system made the design process
easier, while others would provide challenges.
A plus for the designers was that the Five-seveN
(5.7x28mm) cartridge produces a substantially smaller
volume of combustion gases than the 5.56x45mm round.
Less gas means that the suppressor has less work to
do, so the Gemtech team was able to make the SP90
shorter, smaller in diameter and substantially lighter
than previous designs.
Most of Gemtech's design effort focused on engineering
a revolutionary baffle stack that would not increase the
P90's cyclic rate beyond acceptable limits. This challenge,
which one would expect from any compact blowback
weapon, appears because a suppressor increases back
pressure, which increases the cyclic rate of the weapon.
At least theoretically, a suppressor could increase the
back pressure of any compact blowback weapon to the
point that the magazine spring does not have enough time
to present the next round for the bolt as it cycles forward.
Thus a design goal for any compact weapon is to tune
the design of a suppressor so that bolt speed (i.e., cyclic
rate) of the suppressed weapon falls within the optimum
range for both the weapon itself and its magazine. Thus
the contradictory challenges are to minimize back pressure
for optimum reliability while creating maxirnum turbulence
inside the suppressor to optimize the amount of sound
reduction. In order to meet these challenges, Gemtech
developed a baffle stack in which no two baffles are the
same design.
Another design challenge was to develop a robust and
foolproof quick mount for the SP90 suppressor. Since it
proved impractical to design a suppressor mount that
would directly latch onto the outstanding FN muzzle
brake, the Gemtech team decided to marry their Bi-Lock
snap-on quick mount with the FN muzzle brake.
SP90 Design
Gemtech's remarkable spring-loaded Bi-Lock mounting
system provides excellent alignment with the P90 barrel
and a robust means of attaching the SP90 suppressor
that never loosens during firing (unlike screw-on suppressors
using a single-point mounting system, which tend to
loosen when subjected to semiautomatic or full-auto
firing, unless permanently attached with ROCKSETT
sealant or silver solder).
The name of this patented Bi-Lock mounting system
comes from the two alignment lugs on the muzzle brake,
which engage a spring-loaded collet in the back of the
suppressor. The moving parts are sealed to minimize
fouling from carbon and powder residue. To install
the Gemtech SP90 suppressor on a barrel fitted with
a Bi-Lock muzzle brake, simply align the suppressor
with the brake, push down and rotate the can 90 degrees
clockwise (as seen from the front) until the device
can no longer be rotated, and allow the spring pressure
to lock the suppressor firmly against the Bi-Lock's twin
lugs.
Each lug has a different size, so there is only
one way to install thesuppressor. This feature minimizes
the shift in the point of impact whenever the suppressor
is mounted and keeps the shift repeatable (i.e., predictable).
Since stops in the mount prevent rotating the suppressor
past the locking recesses in the interface piston that
mate with the compensator lugs, the mounting procedure
is both positive and very fast. Furthermore, the amount
of pressure generated by the intemal spring during
mounting is considerably less than some quick mounts
I've used on other weapons, making the installation
process easier and faster, without sacrificing security.
When removing the suppressor soon after firing, be aware
that the silencer could be dangerously hot. Use a heavy
glove, hat or other protection to avoid burns. To dismount
the Gemtech SP90, push it backward about 0.1 inch (3 mm)
until the suppressor can be rotated counterclockwise
(as seen from the front). Rotate the can 90 degrees
and pull the suppressor clear of the flash hider. The
Bi-Lock mount permits installing or removing a sound
suppressor in just 1.5-3 seconds. It is safe to say that
the Bi-Lock mount is an impressive engineering achievement.
The Gemtech SP90 suppressor is constructed from 304
stainless steel tubing, 303 stainless steel barstock,
hardened 440C stainless steel for the interface piston,
and Inconel for the blast baffle at the rear of the baffle
stack. Inconel is particularly resistant to the heat
and erosive effects of hot combustion gases, especially
when the suppressor is subjected to fullauto fire.
The Bi-Lock compensator is machined from 4140 steel
which is then hardened. The SP90 is 7.25 inches (18.4
cm) long and 1.37 inches (3.5 cm) in diameter, and the
suppressor weighs 19.4 ounces (550 grams). All suppressor
components are coated in a matte black oxide, and the
interface piston receives an additional coating of Sandstrom
Products 9A Dry Film Lubricant to enhance corrosion
resistance,
From a subjective point of view, the relatively modest
length and weight of the SP90 gives the suppressor
excellent handling characteristics when mounted on
the FN P90. Whether engaging targets at arm's length
or at 100 yards (91 meters), target acquisition was very
rapid and hit probability was outstanding. The sound
signatures produced by the suppressed P90 were quite
impressive. When using the supersonic SS190 ammunition,
the surprisingly mild cough of the suppressor was
followed by bullet flight noise, which was a muted
and rather eerie ripping sound that ended with the
distinctive thud of bullet impact. When using subsonic
SB193 subsonic ammunition, the muzzle signature seemed
dramatically quieter than an H&K MP5 SD, bullet flight
noise was a barely perceptible hiss, and the noise of
bullet impact was easily the dominant sound. While
this is a very interesting design that produces a satisfying
sound signature when fired with either supersonic or subsonic
fodder, there is no substitute for rigorously evaluating
the performance of a suppressor with repeatable and
standardized scientific methodology. To this end, I tested
the performance of the Gemtech SP90 suppressor using
the following procedures.
Performance
Suppressor performance was determined by measuring
sound signatures using the equipment and procedures
specified at the end of Chapter 5 in the book Silencer
History and Performance ($55 postpaid, Wideworld,
Dept. SAR, P.O. Box 1827, Conway, AR 72033). The
microphone was placed 1.00 meter to the left of the
suppressor or muzzle according to U.S. Army testing
procedures specified in MIL-STD-1474C. The ambient
temperature during the testing was 73°F (23°C),
and the speed of sound was 1,132 fps (345 mps).
Velocities were measured in feet per second using
a P.A.C.T. MKIV timer/chronograph with MKV skyscreens
set 24.0 inches apart and the start screen 8.0 feet
from the muzzle (P.A.C.T., Dept. SAR, P.O. Box 531525,
Grand Prairie, TX 75053, 214-641-0049). Atleast 10
rounds were fired to obtain an average sound signature
or muzzle velocity.
Two kinds of 5.7x28mm ammunition were used for the
study. The supersonic SS190 round has steel core in
front of an aluminum core toward the base, a projectile
weight of 31.0 grains (2.02 grams), and a nominal published
velocity of 2,345 fps (715 mps). The subsonic SB193 round
is a lead core boat tail with a length of 0.753 inches
(19.1 mm) and a projectile weight of 55.0 grains (3.58 grams)
in front of 2.0 grains (0. 13 gram) of ball powder. The
SB193 round is still under development at the time of
this writing, and an improved variant of the subsonic
round is scheduled for field trials in the spring of 1998.
Therefore, any data reported here on the subsonic
round must be regarded as provisional.
The sound signatures, which are more properly called
sound pressure levels (SPLs), appear in
Table I along
with some comparative data for reference. Since the
FN P90 might compete against both 5.56x45mm and 9x19mm
weapons for law-enforcement applications, data on both
categories of weapons are included. Unsuppressed and
suppressed versions of the M4A1 were tested at 50°F
(10°C). The MP5 and MP5 SD were tested at 71°F
(22°C). Unsuppressed and integrally suppressed
.22 rimfire rifles were tested at 83°F (28°C)
to provide a baseline for sound signatures significantly
less than normally encountered in the tactical environment.
The net sound reductions appear in
Table II. Figures
1-3 compare aspects of the extemal ballistics (velocity,
trajectory and bullet drop) produced by the SS190 FMJ
round fired from a P90, a Winchester USA 9x 19mm FMJ
round with a 115 grain (7.48 gram) FMJ projectile fired
from an H&K MP5 submachine gun, and an M855 5.56x45mm
round with 62 grain (4.03 gram) projectile fired from an
M4A1 carbine. The P90 produces a projectile velocity
that falls in between the M4A1 and MP5 and provides
performance reminiscent of (but a bit less than) the
venerable old .22 Hornet, which was used in several
survival weapons once issued to the U.S. Air Force.
Thanks to the fairly brisk muzzle velocity and the P90's
high sights, Figure 2 shows that the P90's trajectory is
remarkably similar to the M4A1 out to the P90's effective
range of 150 meters (137 yards). Clearly, an operator
of average skill will obtain much better hit probability
or shot placement with the P90 than with the MP5 simply
because of the flatter trajectory provided by the SS190
round.
Mounting a suppressor on the P90 does have an effect
on projectile velocity. The SS190 round produced a
muzzle velocity of 2,339 fps (713 mps) when fired
without the suppressor mounted on the P90 and 2,262
fps (689 mps) when suppressed. The SB193 subsonic
round produced a muzzle velocity of 998 fps (304 mps)
without a suppressor and 951 fps (290 fps) when the
suppressor is mounted. Velocities decrease slightly
when the suppressor is fitted to the weapon since the
increased back pressure causes the blowback bolt to
begin extraction sooner after ignition than the unsuppressed
weapon. As Figure 4 shows when comparing bullet
trajectories of suppressed versus unsuppressed P90s,
this slightly reduced velocity when the suppressor is
mounted has almost no effect on practical external
ballistics when using the standard SS190 supersonic
round, and should have even less effect with the
subsonic round since there is sig-nificantly less velocity
change in suppressed versus unsuppressed mode. A
discussion of terminal ballistics is beyond the scope
of this study. From an operator's point of view, however,
there are a number of conclusions to be drawn about
the P90 Personal Defense Weapon and the Gemtech
P90 suppressor designed for the weapon.
Conclusions
The P90 is compact, handy in close quarters, and yet
provides rapid target acquisition and outstanding hit
probability out to 150 meters. When fitted with the
Gemtech P90 suppressor and using supersonic ammunition,
the weapon is significantly quieter than a suppressed
M4A1 carbine. This has direct implications regarding
command and control in confined spaces, as well as
both short-term and long-term hearing loss experienced
by personnel operating in limited spaces. When using
subsonic ammunition, the suppressed P90 is dramatically
quieter than an H&K MP5SD and is even quieter than
some integrally suppressed .22 rimfire rifles, making
a very stealthy weapon. The Gemtech suppressor
will tolerate an unprecedented amount of full-auto
fire for an intermediate cartridge, mounts or dismounts
in the time required for a magazine change, and will
not loosen during prolonged firing.
Assuming the terminal ballistics are suitable, the FN
P90 with Gemtech suppressor seems even better suited
for law-enforcement applications than for its originally
intended role as a military personal defense weapon.
Whether used as an entry weapon or a replacement
for shotguns, submachine guns and carbines of pistol
caliber in the squad car - the P90 seems to hold a
great deal of potential for law-enforcement applications,
especially when equipped with the outstanding Gemtech
P90 suppressor. Fabrique National Herstal SA of Belgium
is now entering the law-enforcement market.
The Gemtech SP90 suppressor removes more of the
high-frequency noise than the typical suppressor designed
for intermediate rifle cartridges, so the lower pitch sound
signature of the Gemtech suppressor actually seems quieter
to people with a normal range of hearing than the numbers
in Table I would otherwise suggest. The Gemtech SP90
suppressor provides excellent sound reduction, no adverse
effects on reliability or accuracy, a relatively light and
compact package, and superior durability when subjected
to full-auto fire compared to previous generations of
suppressors. The Gemtech SP90 represents an impressive,
state of the art suppressor, and I can recommend it
enthusiastically. [It is available exclusively from FN
Manufacturing, Inc.]
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