Gemtech HDM Owner's manual

TM-HDM
OPERATIONAND MAINTENANCE
OF SOUND SUPPRESSOR
MODELHDM
Before using this suppressor,
be certain you have read and
understand this manual.
Manufactured by
GEMTECH
Div. of Gemini Technologies, Inc.
P.O. Box 140618
Boise, Idaho 83714
ISSUED:April 2017

 WARNING  
Because sound suppressed weapons make
less noise than non-suppressed weapons, it is
easy to forget that they are still firearms. It is of
vital importance to remember that a sound sup-
pressed firearm is just as dangerous as a non-
suppressed one, and the same safe handling re-
quirements apply.
Historical References Cited:
THETRUTHABOUTGUNS.COM
MODERNFIREARMS.NET
COPYRIGHT NOTICE:
©2017 Gemini Technologies, Inc
All rights reserved. The contents of this publication may not be reproduced
in any form or by any means in whole or in part without the prior written
permission of the copyright owner.

HDM
OPERATIONALMANUALFOR
INTEGRALLYSUPPRESSED
HIGHSTANDARD H-D MILITARYPISTOL
WITHINTEGRALMODELHDMSUPPRESSOR
Manufactured by
GEMTECH
Division of Gemini Technologies, Inc.
P.O. Box 140618
Boise,Idaho 83714-0618
Phone: [phone]
FAX[phone]
CONTENTS:
Historical Information ....................................................................... P. 2
AmmunitionRecommendation ......................................................... P. 3
Photo: Original and Reproduction HDM........................................... P. 4
Cleaning & Maintenance, Disassembly ........................................... P. 5
Reassembly ..................................................................................... P. 6
Cross Sectional Drawing HDM Suppressor ..................................... P. 7
Physical Specifications.................................................................... P. 8
Limited Warranty and Repair Policy................................................ P. 9
GEMTECHPROPRIETARY
Thisdocumentcontains proprietary informationofGemtechand is
submittedtothereceiverinconfidence.Anyreproduction,useand/
ordisclosure of thisand/orany portionthereofis expresslyprohib-
ited without the express written permission of Gemtech

SOUNDSUPPRESSORMODELHDM P.
 WARNING 
Failure to follow installation and maintenance instructions
detailed in this manual can result in potential for serious in-
jury to the user and damage to the weapon. Firearm sound
suppressors are user attached firearm muzzle devices, and as
suchare subject toimproper attachment unlessthe properproce-
dures outlined in this manual are followed.
MANUFACTURER’SDISCLAIMER
The manufacturer is not responsible for improper usage of this prod-
uct. This product is potentially dangerous, and as such it is the user’s
responsibility to understand and implement its proper use. If you do
not understand the instructions in this manual, please contact the
manufacturerfor further clarification.
HISTORY OF THE SILENT H-D MILITARY PISTOL (HDM)
In 1942, the War Department ordered 34,000 Model H-D High Stan-
dard pistols for theArmy to use for basic pistol training. The large frame H-
D, originally introduced in 1940 as an inexpensive alternative to the Colt
Woodsman, had much the same feel, operation, and sights of the Colt 1911
and it was thought that these simple guns could be used to introduce new
shooters to the fundamentals of pistol marksmanship before moving on to
the Colt .45ACP. Besides ease of use, the price tag was also a huge selling
point; the 22 LR was cheaper by far to shoot and allowed valuable war
ammunition to be sent to the front rather than stockpiled at training depots.
The model H-D pistol was manufactured for the civilian market until 1955
when it was replaced by the Olympic series.
During World War II, US secret operatives found themselves in need
ofsmallcaliber suppressed pistols. In responseto this, the OSS (forerunner
of the CIA) ordered a batch of the model H-D from High Standard featuring
an integral sound suppressor. From about October 1943 to March 1944 just
over 2600 H-Ds were made with integral suppressors for use by the OSS,
also known as the iMS (Military-Silent) variant. These guns used an integral
suppressor designed by Electric Bell Laboratories that dropped the sound
levels of the pistol by approximately 20 dB, or about the sound of a cough.
Delivered to the War Department, they were shipped overseas for immedi-
ate use and today a handful still exist in private collections and museums.
It’s believed that as many as 400 of these are still in CIA and DOD armories
2
today.

SOUNDSUPPRESSORMODELHDM P. 3
The original 6¾ inch barrel was reduced in diameter and perforated
with four rows of eleven 1/8 inch holes. The volume between the outside of
the barrel and the approximately eight inch long outer tube was filled with a
stack of brass screen washers to function as a packing material. Forward of
themuzzlewasa stack of similar screen washers witha smaller central hole
to pass the bullet extending to the front cap. The intent was to replace the
screen washer packing every 200-250 rounds – a task that was difficult at
the armorer level and impossible in the field. Packing replacement became
almost impossible if the interval extended past 500 rounds.
The outer tube and front end cap were mild steel. Original specimens
were finished with a standard black oxide (“blued”) finish while subsequent
units has a dark grey phosphate (Parkerize) finish.
Various models of the .22 caliber High Standard pistols, including the
H-D Military have been suppressed by a number of manufacturers. One
company,Automatic Weapons Co in New Mexico in the 1980s, built a num-
ber using a shorter tube with a replaceable copper packing material based
loosely on the original OSS design but more similar to their suppression of
the Ruger Mk1 pistol.Although simpler to repack, service was still required
at intervals of 300-350 rounds.
GEMTECH’S HDMs SUPPRESSION OF THE H-D MILITARY
In 2016, the Gemtech custom shop revisited the OSS suppressed H-D
Military pistol with the goal being to develop a highly efficient integrally
suppressed pistol with easily serviced modern parts that required no part
replacement. Further, the requirement was that the cosmetics had to be
such that it was indistinguishable from the original OSS version. The result-
ing design is an improvement on Gemtech’s Quantum integral Ruger MK-2
pistol. While retaining velocity control to permit the use of HV .22LR ammu-
nition, the Gemtech HDM suppressor achieves a sound reduction in excess
of 35 dB as contrasted to the original OSS design of 20 dB. Photographs of
the original and Gemtech replica are on the next page.
AMMUNITION RECOMMENDATIONS
Special barrel modifications allow the use of both standard and high
velocity ammunition, although the use of standard velocity loadings will be
more pleasing. The weapon functions best using Gemtech subsonic .22LR
ammunition with the 42 grain bullet.

SOUNDSUPPRESSORMODELHDM P. 4

SOUNDSUPPRESSORMODELHDM P. 5
 DANGER 
Before performing any maintenance operation, always
remove the magazine from the firearm, open the action, and
visually ascertain that the chamber is empty and the weapon
unloaded. Failure to do so can result in potential for serious
injury to the user and others in the vicinity.


Always read the warning label on any cleaner or solvent,
and remember that virtually all solvents are inherently dan-
gerous and potentially toxic. Always use adequate ventila-
tion and both skin and eye protection when using organic
solvents.
CLEANING and MAINTENANCE
TheHDMsuppressor can be totally disassembled by theuserforclean-
ing and maintenance. It is strongly recommended that disassembly and
cleaning be performed at intervals of 250 rounds or less. Longer intervals
will result in greater difficulty removing the baffle stack.
1. Remove the magazine from the weapon, open the action, and visually
ascertainthat the weaponisunloadedwithnothingremaining in thecham-
ber.
2. Remove the 8-32x1/8" setscrew from the bottom rear of the suppressor
tube with a 5/64” hex key.
3. While holding the barreled receiver in one hand, firmly grasp the sup-
pressor tube with the other hand and unscrew.
4. While apart, check (and replace if necessary) the small “O” ring gas seal
intherearmount.Replacements are available at any hardware orplumb-
ing store and measure 3/4 inch outside diameter with a 1/16 inch thick-
ness.
6. Unscrew the stainless steel sleeve from the barrel covering the barrel
ports.Check and cleanthe barrel portsifnecessary.Ifany lead is present
in the port, it can be pushed out with a paper clip or other sharp object.
7. At this time, clean the bore of the weapon utilizing any method desired.

SOUNDSUPPRESSORMODELHDM P. 6
8. Unscrew the front end cap from the tube. Using a 3/8 inch wood dowel,
push the baffle stack out from the rear. Gentle tapping with a small
hammer is acceptable. There are seven baffles and a wave spring.
9. There are no perfect carbon solvents. Softening of the carbon deposits
can be performed with LRM Carbon Cutter. A reasonable alternative is
OxyClean detergent in water. Aheated ultrasonic tank may be used.
10. Do not use the vinegar-peroxide internet favorite as it will damage the
aluminumbafflesandmaydamage the black oxide finish of thetubeand
end cap.
11. Following cleaning, rinse thoroughly in warm water followed by drying
and oiling the steel parts inside and out.
REASSEMBLY
Reassembly is the reverse of
disassembly. The first step is reas-
sembly of the baffle stack. There are
three different baffles (all K-type),
andtheirstackingorder is important.
The five middle baffles have index-
ing tabs. The rear (blast) baffle dif-
fers from the others in that it has a
hole in the flat portion of the “K.” The
front baffle differs in that it does not
have the locating tabs.
Thesimplestmethodofreassemblyistostackthebafflesintheproper
sequence and orientation on a 1/4 inch diameter rod or dowel approxi-
mately 9 inches long. Please refer to the drawing next page.
1. Place the front baffle, cone down, on the rod. This is the baffle with no
locating tabs on the end of the cone. Orient this baffle conveniently for
reference.
2. Stack the next five baffles on top of the front baffle, rotating each 180° to
the one below. The tabs engage notches in the flat portion of the baffle
below.
3. Stack the blast baffle, again oriented 180° to the one below.
4. Last, place the wave spring on the blast baffle. Be sure the tabs engage
in the notches and the baffles are stacked smoothly.

SOUNDSUPPRESSORMODELHDM P. 7

SOUNDSUPPRESSORMODELHDM P. 8
5. Without moving the stack, slide the outer tube over the stack until the
entire stack is within the outer tube.
6. Invert the suppressor while holding the stack in place against spring
tension and screw in the front end cap. Gently snug the end cap. It is
neither necessary nor desirable to tighten it any more than light finger-
tight.
8. Apply a thin layer of grease or Vaseline on the “O” ring to provide a gas
seal and ease removal. Replace the “O” ring, if necessary.
9. Replace the diffuser with the open end of the cup to the rear of the
weapon. The diffuser threads onto the barrel.
10. Screw the suppressor assembly onto the barrel until the witness marks
align on the under side. Replace the 1/8” long 8-32 setscrew.
11. Be sure to oil all steel parts to prevent rust.
PHYSICAL SPECIFICATIONS
Parameter Reproduction Original
Suppressor Length (inch) 7.5 7.75
Barrel Length (inch) 4.1 6.75
OverallLength (inch) 14 13.78
Weapon weight (ounce) 40.2 48
Sound reduction (dB) 32 20
MATERIALS (GEMTECH HDM Reproduction)
Outer Tube, endcap: 4130 steel, black oxide finish, same as original
Diffuser: 304 stainless steel.
Baffles: 7075 aluminum (high tensile strength)