Armored 
Medical Research Laboratory 
Fort Knox, Kentucky 
INDEXED 
PROJECT NO-.6- VISION IN TANKS 
Report On 
Sub-Project No. 6-15 - Study and Development of New Instruments 
for Indirect Fire Control 
SUBJECT: PARALLELOGRAM MOUNTING OF REFLEX SIGHT 
-E01U5O CAL. ANTI-AIRCRAFT MACHINE GUN 
Project No. 6-15 
14 October 1944 ARMORED MEDICAL RESEARCH LABORATORY 
Fort Knox, Kentucky 
Project Noo 6-15 
File No, 413o74-4 SPUEA 
14 October 1944 
PARALLELOGRAM MOUNTING OF REFLEX 
SIGHT FOR 50 CAL. ANTI-AIRCRAFT MACHINE GUN 
1. PROJECT: No. 6 - Vision in Tanks; sub-project 15 - Study and 
Development of New Instruments for Indirect Fire Control0 
a. Authority: Letter Commanding General, Headquarters Armored 
Force, Fort Knox, Kentucky, File 400,112/6 GNOHD, Dated September 24, 1942. 
> y * £ 
b. Purpose: To develop a mount which v.ould place the reflex 
sight above the smoke, be convenient to the gunner, and absorb recoil shocko 
20 DISCUSSION: 
ao Facts pertinent to the development are as follows: 
(1) This project was jointly initiated by the Gunnery De- 
partment of The Armored School and by the Weapons 
and Ammunition Section of the Armored Board. 
(2) The parallelogram mount was first designed and later 
improved by the Armored Medical Research Laboratory. 
(3) Three (3) mounts were fabricated locally by a contract 
with the Armored Board and a similar mount was fabri- 
cated by the University of Rochester. 
(4) The mount was designed for a reflex sight developed by 
the University of Rochester under an NDRC contract at 
the request of the Armored Board. While specifically 
the mounts were developed for a 300 mile an hour lead 
ring type reflex, it is equally adaptable to the 400 
mile an hour lead ring type developed for the Anti- 
Aircraft Artillery Board. 
b. The following requirements were considered essential in the 
design: 
(1) That the sight be elevated 20 to 25 inches above the gun 
in order to avoid obscuration by smoke. 
(2) The reflex sight must be mounted so that the eye can be 
1 held vTithin one or two inches of the window in order 
to secure full advantage of the wide field (300 or 
400 mile lead ring circles). 
(3) Because of the necessary contact between head and head- 
rest, shock of recoil must be absorbed in order to 
eliminate jarring ano loss of vision from vibration. 
c. The sight mount comprises the following general characteristics: 
(1) A four-member parallelogram is attached to the gun cradle 
supporting trie sight so that the eye is approximately 
2$ inches above the barrel of the gun in the middle 
range of operation.(See drawings & specifications attached, 
(2) A restoring spring device keeps the normal position of 
the sight suitably placed for the gunner. During changes 
of elevation, the level at which the eye position is 
maintained does not appreciably change0 As one approaches 
higher elevations, the eye position moves in somewhat to 
accommodate the natural forward movement of the gunner 
as he depresses the grips. 
(3) The spring positioning device satisfactorily absorbs the 
shock of recoil except at very low elevations where 
there is some residual disturbance to the head. 
(4) A spring detent and shock absorbing mechanism was incor- 
porated later in the head-rest permitting a movement 
of 1/2 to 3/4 inches which satisfactorily removes ob- 
jectionable shock even when firing at low elevations0 
t 
(5) The entire assembly can be quickly folded flat to the 
gun when in carrying position. 
(6) A modification was introduced (see supplementary drawings 
1 and 2) which allows a quick removal of the sight 
without disturbing boresight adjustmerit. 
(7) Experiments were conducted on spring character which re- 
sult ed in the thinner leaf type shown in supplementary 
drawing 3» 
d. Tests conducted in conjunction with the Armored Board and The 
Armored School established the following: 
(1) The placement of the sight avoided obscuration. 
(2) Head shock was at no time objectionable, being practically 
non-existent in the normal anti-aircraft elevation ranges. 
2 (3) Accuracy of alignment retention appeared to be satis- 
factory as tracer fire narrowed to a stream comparable 
to the inherent dispersion of the gun. . No accentuation 
of whip could be noted. 
(4) When crews became accustomed to the use of the rings for 
lead, marked improvement in effectiveness was noted. 
(One crew obtained as high as 12 hits in 1000 rounds 
on a towed sleeve 15 feet in length and 2 feet in dia- 
meter at 600 yards.) 
(5) It was not possible to obtain statistically dependable 
appraisal of the device, but the more experienced anti- 
aircraft gunners felt that many times increase in ef- 
fectiveness would be obtained with proper training. 
e. Tests conducted by Anti-Aircraft Artillery Board may be commented 
upon as follows: 
(1) The primary purpose of the mount to raise the sight above 
obscuration by smoke was not mentioned. 
(2) Suitable platform inevitably necessary for employment of 
subject sight and mount was not employed; hence erroneous 
conclusion that the sight was not well positioned. This 
conclusion was exactly contrary to all our findings. 
(3) No adeouate statistics were offered to indicate the possible 
improvement in anti-aircraft fire. 
3. CONCLUSIONS: 
a. The subject reflex sight mount provided an adequate positioning 
of the sight close to the gunner's eye under all conditions of anti-aircraft 
fire. 
b. Shock disturbance was satisfactorily removed. 
c. The positioning avoided previous difficulties of obscuration 
encountered with all types of anti-aircraft sights tried. 
d. Boresighting and alignment were adequately attained. 
4. RECOimmATIONS: 
a. That the parallelogram mount be adapted for armored vehicles 
employing 50 Cal. machine gun for anti-aircraft protection. 
3 bo That platforms be provided in armored vehicles to secure the 
proper height for the use of subject parallelogram sight. 
The conclusions and recommendations set forth above have been concurred 
in by Headquarters, Armored Center, Kent C. Lambert, Colonel, Acting Chief 
of Staff, with the further recommendation that with the consideration for 
adoption of this mount, more stable gun mounts for vehicular mounted o50 
caliber machine guns, be developed to take advantage of the inherent good 
qualities of the parallelogram mount. 
Submitted by: 
F. S. Brackett, Lieut. Colonel, Sn C 
APPROVED , 
■ ' WILLARD MACHLE 
Colonel, Medical Corps 
Commanding 
7 Incls 
3 Blueprints 
3 Drava ngs 
Specifications 
4 SPECIFICATIONS FOR REFLEX SIGHT MOUNT 
50 Calo Anti-Aircraft Machine Gun 
Detail 
No. 
No. 
Req'do 
Size, no allowance 
Material 
1 
1 
3/8 dia. x 26 lgo 
Steel rod 
1A 
2 
1/8 x 2-1/4 x 1-19/32 
Steel 
IB 
2 
1/16 x 3/6 x 1-1/2 
Spring steel 
2 
1 
3/8 x 1-3/4 x 2-3/8 
Brass 
3 
1 
1/4 X 7/8 X 2-3/4 
Brass 
4 
1 
1/2 x 7/8 lgo 
Brass 
5 
1 
7/8 O.D. x 1/64 thick 
Spring steel 
6 
1 
1/4 - 20 st'd. 
Wing nut 
7 
1 
3/8 dia. x 1-1/4 lg. 
Brass 
8 
1 
1 dia. x 5/8 lg. 
Brass 
9 
1 
23/32 O.D. x 3/16 I.D. x 1/32 thick 
Steel . 
10 
2 
Aluminum casting 
11 
2 
1/2 dia. x 2-3/16 1g. 
Drill rod 
12 
4 
1/16 x 1/2 x 3 1g. 
Spring steel 
13 
2 
1/16 X 1/2 X 3 Ige 
Spring steel 
13A 
2 
1/16 x 1/2 x 1-15/16 lg. 
Spring steel 
13 B 
2 
1/16 x 1/2 x 1-11/16 lg» 
Spring steel 
13C 
2 
1/16 x 1/2 x 1-7/16 lg. 
Spring steel 
13D 
2 
1/16 x 1/2 x 1-3/16 lg. 
Spring steel 
13E 
2 
1/16 x 1/2 x 15/16 lg. 
Spring steel 
14 
2 
5/8 x 7/8 x 1-1/4 
Brass 
15 
2 
3/4 dia. x 15/16 lgo 
Brass 
16 
1 
3/16 x 3/4 x 20 lg. 
Steel 
17 
1 
Iron casting 
18 
1 
7/16 x 1-3/16 x 1-1/2 
Steel 
19 
1 
1/16 x 1 x 2 
Spring steel 
20 
1 
Aluminum casting 
21 
1 
7/16 dia. x 1-5/16 lgo 
Steel 
22 
1 
7/8 x 1 x 3 
Steel 
23 
2 
Aluminum casting 
24 
2 
1/2 dia. x 2-1/4 lg. 
Drill rod 
25 R.H. 
1 
Iron casting 
25 L.H. 
26 
1 
Omitted by revision 
Iron casting 
27 
2 
1/2 dia. x 6-1/16 lg. 
Drill rod 
28 
1 
Aluminum casting 
29 
2 
Aluminum casting No. Keq'd. 
Standard Stock 
20 
Washer, lock for #10 machine bolt (steel) 
4 
#10-24 x 1 hex. head machine bolt (brass) 
threaded 3/3 from end 
3 
#10-24 hex^.head machine bolt nut (brass) 
1 
#8-32 x 3/8 1g. flat head machine screw (brass) 
2 
#8-32 x 5/8 1g. fillister head cap screw (brass) 
1 
#52 x 7/8 1g. drill rod (.063 dia.) 
1 
#52 x 3/8 1g. drill rod (.063 dia.) 
12 
#10-24 round head machine screw (brass) 
8 
#2/0 x 1 1g. taper pin 
4 
3/8 I.D. washers (steel) finished 
4 
3/32 dia. x 1 1g, spring steel cotter 
2 
#10-24 x 1-5/8 hex. head machine bolt (brass) 
2 
#10-24 x 1-1/4 hex. head machine bolt (brass) 
4 
3/8 - 16 N.C. slotted nut (steel) 
2 
#30 x. 7/8 lg0 drill rod (.12? diao) 
2 
#8 - 32 x 1/2 flat head machine screw (brass) 
- 2 
#6 - 32 x 7/16 round head machine screw (brass) 
2 
Washers, lock (steel) for #6 machine screw 
1 
3/16 x 1-3/4 1g. flat head rivet 
1 
3/32 dia. x 1/2 soring steel cotter 
1 
1/4 - 20 x 3/4 round head cap screw (steel) 
1 
Washer, lock (steel) for 1/4 cap screw 
1 
1/4 - 20 x 5/8 Allen oval pt. set screw 
1 
Nut, lock (steel) for 1/4 ~ 20 set screw 
7 
5/16 - 18 x 7/8 1g. hexo head bolt (steel) 
7 
Washer, lock (steel) for 5/16 bolt A/ X" 7 ceMM 
4 /& 
MM 
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4 
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