Colt Salvo Squeeze Bore (SSB)

The Colt SSB work was based on previous work by Russell Robinson who filed for the patent
for the SSB concept in 1961 (# 3,450,050) although his work started long before that time.

This Colt development work was done in the late 1960s and early 1970s. What appears to be a
final report was dated January 1971. The purpose of the project was ito increase hit probability
and target saturation by use of multiple projectiles. Colt demonstrated the effective of the
concept in three calibers; .50/.30, 7.62/.220 and 9mm/.30. The concept was also tested in .45 and

It appears that the initial work was in .50/.30 for the Browning M2 machine gun fitted with a
barrel with included a conical taperbore adapter near muzzle. This system used 5 projectiles
per round so that the 600rpm rate of fire of the M2 provided 3000 projectiles per minute with no
other modification of weapon but barrel. This was apparently the only aspect of the SSB that
reach operational use with modified weapons being used operationally with Navy Swift boats in

The 7.62/220 tested on M14 using three 55gr projectiles in each cartridge. Specimens of this
cartridge are relatively rare and it appears to have only been a test program.

The 9mm/.30 was tested extensively and ammunition with both Colt headstamps and with Israeli
military headstamps were apparently produced in at least limited quantities. There are a wide
variety of experimental/test cartridges, most of which used assorted cases so the headstamps
have no significance. The material below illustrates the concept and provides the performance
of the ammunition. It also includes the performance of the ammunition. Many of the
experimental loads are illustrated.
Headstamp used on Colt 9mm SSB
production ca '70-'71
Headstamp used on 9mm SSB
produced for Israel. These are Israeli
supplied cases so production was
likely in late 1970 or early 1971.
Box label from for the Colt 9MM SSB headstamped
ammunition. No box has been identified for the Israeli
Left to Right:
  1. A very early round-Tiplex-with the bullets glued together (170.2gr oaw, 1.160" oal). Very few of these
    loads were made and they didn't work very well as the last bullet tended to skew in the barrell
  2. Very early test load-reportedly a Duplex-Probably the first of the Colt tests. This load comes in two oal
    (1.043" and 1.075") with different lengths of plastic visable at the case mouth. The weights are 186.5gr
    and 188.5gr respectively. These may be triplex loads.
  3. Another version of #2 above but this one with a red tape only visable at the case mouth (1.046" oal) and
    the weight is 186.6gr. The Woodin Laboratory has two seperate bullets which may be associated with
    this cartridge. Based on these two bullets, this may be a triplex load. The two seperate bullets weigh 25.1
    gr and 125.7gr
  4. In the Koch collection were a number of dummy rounds made up on the commercial W-W dummy case
    which lacks both primer and primer pocket. Most were badly scratched from use but this one was in good
    condition (159.6gr oaw, 1.17" oal). The plastic jacket on this load is molded.
Box label from for the Colt 9MM SSB headstamped
ammunition. No box has been identified for the Israeli
Box label from for the Colt 9MM SSB headstamped
ammunition. No box has been identified for the Israeli
Box label from for the Colt 9MM SSB headstamped
ammunition. No box has been identified for the Israeli
Box label from for the Colt 9MM SSB headstamped
ammunition. No box has been identified for the Israeli
Box label from for the Colt 9MM SSB headstamped
ammunition. No box has been identified for the Israeli
Box label from for the Colt 9MM SSB headstamped
ammunition. No box has been identified for the Israeli
These three loads all have the Colt headstamp. Some of these cases were used for test
Left to Right:
  1. Another of the experimental loads with the molded and turned jacket. This load with
    the "Colt" headstamped case implies that the molded sabot was probably a test
    program in the 1971 or later time frame. Blind primer pocket (170gr oaw, 1.176" oal)
  2. A dummy round with no primer and a blind primer pocket. The normal triplex bullet
    appears to have slipped into the case because of the lack of powder (165gr oaw,
    1.120" oal)
  3. This is the standard Colt SSB round which is found in the 64 round box illustrated
    earlier (176gr oaw, 1.166" oal). About 18K rounds of this ammunition was produced
    (loaded by IVI of Canada) and all but about 500 rounds were shipped to Israel.
Left to Right:
  1. A late model SSB load with relatively pointed projectile (167gr oaw, 1.153" oal)
  2. A late model triplex load with a projectile with a relatively large tip diameter (167gr, 1.156" oal)
  3. The short length of this bullet indicates it may actually be a duplex load but the weight indicates a
    triplex. Note the late model sabot with the grooves and the recessed tip on the projectile (166gr oaw,
    1.084" oal)
There are a varity of cartridges similar to these, with variations in tip shape and length, and different oal of
the round. Some come from Colt sources and marked "<500 made" and "<100 made". All these loads have
molded bullet jackets.
Left to Right:
  1. Dummy with the late model bullet which is more transparent and has the grooves or slots in the bullet.
    Note the rough texture of the projectiles (155gr oaw, 1.153" oal). This load has a molded jacket.
  2. An early round with the smooth sabot and no primer (155gr oaw, 1.180" oal). Machined nylon jacket.
  3. Another early test load with the smooth sabot. Note the thickness of the projectile viable in the sabot. This
    may be a duplex load because three bullets of this size would take most of the volume of the case (185.7
    gr oaw, 1.131" oal). Machined nylon jacket. Only about 300 cartridge were made with this type jacket.
  4. This round has an unusual bullet in that there is a plastic nipple on the tip of the jacket which covers the
    tip of the bullet. All other known SSB bullets have the tip of the first bullet exposed (164.6gr oaw, 1.149"
Left to Right:
  1. A slightly different bullet with a jacket cast around the bullets and then machined to shape. The
    bullets are solid turned GM, not the lead core bullets like most SSB (103gr, 0.7425")
  2. One of a series of unusual SSB loads with a sabot that appears to be molded and then turned down
    (167.3gr oaw, 1.133" oal)
  3. Another variation with a slightly different bullet ogive (164gr oaw, 1.139" oal)
Early test rounds with various type plastics as sabot. These are clearly early test items since the sabots
lack the vertical scribe marks added to later loads for better separation. All have machined jackets.
These bullets were apparently made by Colt's lab in New York using a different process.
Left to Right
  1. Gray molybdenum disulfide impregnated nylon jacket (164.6gr oaw). Fewer than 800 produced.
    The molybdenum disulfide was intended to reduce the friction. Not too successful.
  2. Black Delrin plastic jacket (166.5gr oaw). Delrin is similar to nylon but more brittle and intended to
    provide for better breakup and seperation. Not too successful. Less than 100 produced.
  3. This is probably a round with an ABS plastic jacket intended to improve breakup (163.9gr oaw).
    Only 100 produced, but apparently another 100 rounds were loaded with slotted ABS jackets.
These three loads all have the Israeli headstamp.
Left to Right:
  1. This is the standard load associated with the Israeli 9mm SSB contract (175.1
    gr oaw, 1.195" oal)
  2. A dummy load with a solid nylon bullet (80.3gr oaw, 1.127" oal). Less than 20
    were made. Most were shipped to Israel.
  3. Loaded round with a slotted jacket (163.3 gr oaw, 1.177" oal). There is also
    a variation of this round with 171.1gr oawand 1.155" oal. these were Colt test
    items put in Israeli cases. This load is one of the few with a machined slotted
    jacket, indicating it is one of the very early slotted jacket loads.
10K empty primed cases were shipped to Colt. All but a few hundred were loaded
and shipped back to Isreal.
Data from test firings on 4/8/70
The material below was sent to me as a packet and is clearly from a test firing of SSB cartridges. There
are a number of envelopes and one was titled 9mm SSB Projectiles. The origin of this material is
unknown. The material includes the following:
  1.    Photo of different SSB bullets with information on each.
  2.   Three photos of SSB bullets in flight (two are reproduced below). The bullets in the top photo
    are shown as three white projectiles at the center right of the photo with the wake visible behind
    them. in the second photo the last bullet can be seen in front of the wooden beam with the other
    two bullets just to the right of it.
  3.   Five targets from test shots (three reproduced below) showing the impact pattern of the
    projectiles. Blue background paper was used to highlight the holes. The brown backing paper for
    the targets was also included.
  4.   An assortment of fired and unfired SSB bullets along with a single bullet that is similar to the
    individual triplex bullets but significantly larger. The base of this bullet is pictured separately. This
    bullet is not similar to any other bullets known to be part of the SSB test series.
  5.    An envelop containing sectioned bullets and a sectioned case and some W-W dummy cases as
    well as a single SSB dummy made using a W-W dummy case without a primer pocket. Two
    identical dummies were found in the collection of Ted Koch who had close relations with Colt and
    was a friend of Rob Roy of Colt. The inclusion of this dummy with the test specimens implies it was
    an item contemporary with the SSB tests in 1970 and is probably a legitimate part of the set of
    SSB loads.
  6.   The final items in the packet were a set of photos of barrel/chamber pressure traces for the five
    test shots as well as traces titled "WW 9MM" dated 9 April 70, the day after the SSB test firing. The
    peak pressure on the W-W shots is about 30K psi while the five SSB traces of 40K to 50K psi.
From Left to Right;
  1. 33.4gr - 0.346" oal
  2. 38.3gr - 0.361" oal
  3. 32.7gr - 0.331" oal
  4. 41.2gr - 0.354" oal
  5. 41.4gr - 0.386" oal
  6. 71.5gr - 0.500" oal - six radial grooves in the base-two visable in photo above
This  photo shows a set of SSB bullets that
came from the Ted Koch collection. Ted
was close to Rob Roy of Colt and had quite
a bit of experimental SSB material. Note
that the weight of these rounds differ a
great deal. on the front row, from left to
1. 102gr
2. 114gr
3. 124gr
4. 140gr-4 bullets

Second row all weigh between 103gr and
105gr with no significant differences except
for some in the base of the projectiles

The last two bullets are from another
collector who had close connections with
Colt. These are two 115gr bullets fired
down different squeeze bore barrels at Colt
early in their 9mm SSB work. One is now
6.53mm and the other 7.64mm.
Left to Right:
  1. Dummy with solid nylon plastic bullet and an inert primer. This bullet has grooves (hard to see) in the
    bullet to simulate the late style bullets (73.9gr oaw, 1.129"oal) the solid molded bullets for these
    dummies were from mold tests, and later used to make dummies which can be found in a number of
    headstamps. About 150 of these were made.
  2. Another dummy without a hole and much shorter. Less than 50 of these were made (70.1gr oaw,
    1.052" oal).
  3. This is a very strange item, and clearly a Colt test cartridge. It has the molded plastic jacket crimped
    tightly in the case, but has only the single bullet in the front of the jacket. The bullet appears to be
    made of lead (93.7gr oaw, 1.108" oal
Close examination under a glass will reveal machining marks on the jacket of many of these bullets. All the
unslotted bullet examined show these marks. Most of the slotted jacket bullets show a grainy surface indicating
they were molded. This grainy appearance also shows up inside the slots. Two of the slotted rounds examined
show machining marks on the jacket and the slots were clearly cut showing machining marks but no grainy
areas. Load #3 immediately above is the only load illustrated with a machined, slotted jacket.
Bullets courtesy of Woodin Lab