[0001] This invention relates to a firing pin block that prevents a firearm from being discharged
with its bolt in an unlocked position. More particularly, it relates to a firing pin
block for a firearm of the type in which a breech bolt has locking lugs and is rotatable
between a position locked to the barrel and an unlocked position, this rotation being
imparted by cam means drivingly connecting the bolt with a reciprocating bolt carrier.
[0002] The idea of blocking a firing pin to prevent the discharge of a rotary-bolt firearm
when the bolt is in an unlocked position is not new. U. S. Patent 2,685,754 to L.
R. Crittendon et al, which has a common assignee with the present application, shows
such a block; and this invention is an improvement to that device. In the Crittendon
Patent, the travel of the firing pin in limited by its retaining pin, which is mounted
in the bolt carrier to extend across a flat on the firing pin. Cam means connecting
the bolt with the carrier are arranged to rotate and lock the lugs of the bolt to
those of the barrel before the carrier completes its forward stroke, allowing some
lost motion at the end (
1f this travel. The dimensions are so selected that until thr bolt has first been locked
and then the lost-motion portion of t.he carrier stroke has been at least partially
completed, the firing pin is restrained by its retaining pin from protruding from
the bolt face far enough to fire a cartridge. On firing, the forward momentum of the
firing pin is absorbed in part by impact against its retaining pin. This may sooner
or later distort the parts enough to interfere with proper operation of the firearm.
In an extreme case, distortion may cause the firing pin to jam with its tip protruding
from the bolt face. Further, the block is inoperative if the retaining pin is broken
or missing.
[0003] Another prior-art design of interest is shown by Patent 3,397,473 to Browning, in
which, in common with the present invention, cam means rotate the bolt as a result
of sliding motion of the carrier. However, forward motion of the firing pin relative
to the bolt is limited only by its engagement with the bolt, or with a retaining pin
mounted in the bolt. Therefore, the firing pin is not positively blocked against protrusion
from the bolt face when the bolt is unlocked, but is merely biased rearwardly by the
firing pin spring.
[0004] Prior-art firing pin blocks for bolt-action firearms are shown in U. S. Patents 2,926,446
to Benson, and 2,976,637 to Robinson. Benson discloses a bolt-action rifle in which
a lug on the firing pin is engageable by a cam on the bolt handle; when the handle
is raised to unlock the bolt, the cam retracts the firing pin behind the bolt face.
Robinson is an example of a hammerless bolt-action rifle in which a firing pin is
cocked rearwardly by a cam on the bolt when its handle is raised, and positively held
by the cam in this retracted position until the handle is lowered to lock the bolt.
[0005] It is the general object of the present invention to provide a firing pin block that
positively prevents the discharge of a rotary-bolt firearm when its bolt is unlocked,
and that will permit firing only after a safe degree of bolt lock-up is achieved.
A further object is to insure positive operation of the block even if the firing pin
spring and retaining pin have been distorted, have failed, or are missing altogether.
Another object is to provide a simple, economical firing pin block for rotary-bolt
firearms that does not require any separate parts, in addition to a bolt, bolt carrier,
firing pin, and cam means drivingly connecting the bolt and bolt carrier, that can
be omitted or lost in assembly.
[0006] Although the firing pin block of the present invention can serve as the sole means
to prevent firing of a rotary-bolt firearm when the bolt is unlocked. it is preferred
to use the system as a fail- safe device, in conjunction with other, conventional
means for preventing firing when the bolt is open. For example, the assignee of the
present invention has for some years made firearms having a trigger disconnector (which
may be integrated with an action bar lock in slide-action models) to prevent firing
when the breech bolt is open. Examples of these devices are shown in U. S.
[0007] Patents 2,675,638 and 2,685,75h to L. R. Crittendon.
[0008] The present firing pin block incorporates an enlarged head or abutment formed on
the firing pin, which is engageable with the rear end of the bolt carrier slide to
block the firing pin from any forward protrusion beyond the bolt face until locking
lugs formed on the breech bolt are at least partially, and preferably fully, locked
into complementary lugs on the barrel or barrel extension. The blocking action is
achieved by coordination of the relative longitudinal movements of the bolt carrier
and bolt with the operation of cam means which drivingly connect them to produce rotary
locking movement of the bolt after it has closed on the barrel breech, and the carrier
continues to slide forwardly. The degree of lock-up that must be attained before firing
becomes possible can be changed by varying these relationships, although it is highly
preferable to delay removing the blockage until after the locking lugs are fully engaged
and the bolt is completely locked.
[0009] The improved firing pin block has an additional advantage in that it mechanically
retracts the firing pin to a position behind the bolt face as the bolt is opened after
firing. The firing pin is thus retracted to a safe position even if the firing pin
spring or retaining pin are broken, distorted, or missing.
FIG. 1 is a fragmentary sectional view in side elevation of a firearm incorporating
a preferred embodiment of the invention, showing the rotary bolt and a bolt carrier
slide at the rear ends of their strokes, and the breech open;
FIG. 2 is a diagrammatic end view showing the angular relationship between complementary
locking lugs formed on the bolt and the barrel, in the open-bolt position of FIG.
1;
FIG. 3 is a view similar to FIG. 1, but showing the firearm with the bolt carrier
approaching the forward end of its stroke, and the bolt closed on the barrel breech
but not yet rotated relative to the bolt carrier, so that no rotation of the locking
lugs has 3 taken place;
FIG. 4 is a view similar to FIG. 3, but showing the firearm with the bolt carrier
moved farther forward relative to the bolt, enough to cause rotation of the locking
lugs to bring the bolt into fully locked-up relation to the barrel, but not yet far
enough to permit firing to occur;
FIG. 5 is a diagrammatic end view showing the angular relationship between the locking
lugs of the bolt and barrel in the locked position of FIG. 4;
FIG. 6 is a view similar to FIG. 4, but showing the bolt carrier moved still farther
forward, to the first position in which firing becomes possible;
FIG. 7 is a view similar to FIG. 6, but showing the completion of the forward stroke
of the bolt carrier, with the parts in their normal firing positions, and the hammer
shown striking the firing pin; and
FIG. 8 is a view similar to FIG. 7, but showing the commencement of rearward movement
of the bolt carrier after firing, to unlock and open the bolt and re-cock the hammer.
[0010] The present invention is equally applicable to manual slide- operated firearms and
gas-operated semiautomatic firearms of the type having a rotary bolt. Since the fire
control system and'the reloading system of the firearm are not directly concerned
with the firing pin block of this invention, and may be of various designs well known
in the art, these systems have been omitted from the drawings. Reference is made to
the aforementioned U. S. Patents 2,685,754 and 2,675,638 for typical examples of firearms
to which the present invention might be applied.
[0011] FIGURES
1 and
2 show a firearm having a barrel 12 formed with a cartridge-receiving chamber 18. A
barrel extension 14 is threaded on the barrel at 13, and is formed with a series of
conventional circumferentially-spaced locking lugs 16. The barrel extension is attached
by a bolt 19 to a forward portion 21 of a receiver 20, which has a socket 23 at its
rear end for mounting a shoulder stock (not shown). An action bar assembly 22 is reciproca
bly slidable in the receiver, and extends forwardly for attachment to conventional manual
or gas operating means (not shown) located at the fore-end of the firearm. The action
bars 22 are interconnected at their rear ends by an integral U-shaped yoke 24, which
fits into a recess 27 in a bolt carrier slide 28 to provide a fixed connection therewith.
A resilient plastic ring 53 maintains correct lateral alignment between the yoke 24
and slide 28.
[0012] A breech bolt 30 is slidably and rotatably received in a bore 29 in the bolt carrier
28. The bolt has an axial bore 32, in which a firing pin 34 is reciprocably slidable
between a retracted position shown in FIG. 1, in which its tip 35 is withdrawn behind
the bolt face 36, and an extended position in which the tip protrudes from the bolt
face, as shown at 35" in FIG. 6, to fire a cartridge (not shown) received in the chamber
18. The firing pin is biased rearwardly by a compression spring 54 received in the
bore 32 and bearing against shoulders 56 and 58, respectively formed in the bolt and
on the firing pin. The firing pin is secured by a retaining pin 60, extending transversely
through a cylindrical shank portion 42 at the rear of the bolt, and cooperating with
a flat 62 milled on the firing pin to limit rearward movement of the firing pin relative
to the bolt. Forward movement of the firing pin relative to the bolt is limited by
engagement of the shank 42 with an enlarged circular head or abutment 48 formed on
the firing pin. (See FIG. 7). The distance that the firing pin tip 35 protrudes from
the bolt face 36 is critical to proper functioning of the firearm. Control of this
dimension in the manufacture of the improved firearm is greatly facilitated by the
fact that the engaging surfaces of the shank 42 and abutment 48 are flat, and parallel
to the bolt face 36.
[0013] The bolt 30 is formed on its exterior cylindrical surface with a pair of similarly-shaped
circumferentially-spaced cam slots 52, of which only one appears in the drawings.
These cam slots cooperate with a pair of cam pins 50 secured in the bolt carrier 28
to produce rotation of the bolt when it is moved axially relative to the bolt carrier.
One of these cam pins may comprise the inner end of a manual bolt-operating handle
(not shown), if desired.
[0014] In the positions of the bolt carrier shown in FIG. 1 and 3, the bolt is rotated to
an unlocked position, in which it protrudes forwardly from the bolt carrier, by movement
of the cam pins 50 to the rear ends of the slots 52. The bolt has a series of circumferentially-spaced
locking lugs 40 around its outer surface; as shown in FIG. 2, these lugs are aligned
to enter freely between the lugs 16 of the barrel extension 14 as the bolt is moved
forwardly by the action bars 22 and bolt carrier 28 between the positions of FIGS.
1 and 3. This angular alignment is maintained during this forward movement by a rectilinear
channel 33 formed in the top of the receiver 20, and extending parallel to the longitudinal
axis of the bolt, for receiving and guiding one of the lugs 40. The carrier 28, which
is guided for rectilinear reciprocation primarily by the action bars 22 riding on
rails 25 formed in the side walls of the receiver 20, also has a guide lug 41 that
is slidably received in the channel 33.
[0015] The rearwardly-extending tubular shank portion 42 of the bolt is slidably received
in a bore 44 formed in a rearward extension 46 of the carrier 28. The enlarged head
or abutment 48 engages the carrier extension 46 to prevent forward movement of the
firing pin 34, in the relative positions of the parts shown in FIGS. 1 and 3.
[0016] The bolt 30 is shown in FIG. 1 protruding forwardly from the carrier 28 to the maximum
extent, as defined by engagement of the cam pins 50 with the rear ends of the cam
tracks 52. This protruding relationship is maintained, as the carrier moves the bolt
forwardly, by the lug 40 sliding in the channel 33. The maximum retraction of the
bolt into the carrier, as shown in FIG. 7, is defined by the cam pins 50 engaging
the forward ends of the cam tracks 52, after these cam means have rotated the bolt
to its locked position.
[0017] A hammer 66 is pivotally mounted on a pin 68 secured in the receiver 20, and is rotatable
clockwise, when released by a suitable trigger and fire control mechanism (not shown)
from a cocked position shown in FIG. 1 to a firing position shown in FIG. 7, in which
it impacts the rear end of the firing pin to discharge the firearm. A box magazine
70 is mounted in the receiver in a conventional fashion to supply a series of cartridges,
each of which is fed successively into the chamber 18 by a forward movement of the
bolt 30. In the illustrated embodiment, the clockwise rotation of the hammer 66 is
limited by its engagement with the magazine 70, as shown in FIG. 7, and the firing
pin is driven forwardly by the momentum of hammer impact imparted to it prior to this
engagement.
[0018] Referring now to FIG. 3, the bolt carrier 28 and action bars 22 are shown moving
forward, in the direction shown by the arrow. The bolt has passed over the magazine
70, where it could have picked up a cartridge (not shown), and its forward stroke
has been terminated by abutment against the barrel 12, in which position it would
have seated the cartridge in the chamber 18. The bolt lugs 40 have passed freely between
the barrel lugs 16, have left the receiver channel 33, and have entered a cylindrical
recess 17 in the barrel extension 14, so that the bolt is now free to rotate. However,
no bolt rotation has yet occurred, since the cam pins 50 have not yet been moved by
the forward travel of the bolt carrier 28 from the rear ends of the cam tracks 52.
[0019] It will be observed in FIG. 3 that a premature release of the hammer 66, which is
possible at this point, will merely impact the head 48 of the firing pin against the
rearward extension 46 of the bolt carrier, since these parts still remain in contact.
Thus the firing pin is blocked and cannot be moved forwardly in the bolt bore 32 at
this time, either by impact of the hammer 66, or by its own inertia if the firearm
is accidentally dropped, even if the spring 54 should be distorted, broken, or missing.
[0020] As shown in FIG. 4, the action bars 22 have carried the bolt carrier 28 far enough
forward relative to the bolt 30, which can travel no farther, to cause the pins 50
to traverse the curved portions and enter into the longitudinal portions of the cam
slots 52, and at the same time to move forward a distance L relative to the bolt.
This distance is slightly more than sufficient to rotate the bolt and engage the bolt
lugs 40 behind the barrel lugs 16, as shown in FIG. 5, to lock the bolt to the barrel
extension 14.
[0021] The firing pin 34, being pressed rearwardly by its spring 54 against the retaining
pin 60 in the bolt, begins to protrude rearwardly from the carrier extension 46 at
the same time as the carrier 28 commences to move forward from the FIG. 3 position
toward that of FIG. 4. The carrier 28 consequently reaches a position in FIG. 4 such
that the gap between the head 48 of the firing pin and the carrier extension 46 is
equal to L, the same distance that the cam pins 50 have moved forwardly in the bolt
30. The parts are so dimensioned that the distance between the tip 35 of the firing
pin and the bolt face 36 is also equal to L.
[0022] If the trigger is pulled at the stage shown in FIG. 4, releasing the hammer 66 to
strike the firing pin at a position 66', it will be seen that the head of the firing
pin can travel forwardly only the distance L before it is stopped at a position 48',
abutting against the carrier extension 46. Therefore the firing pin tip will be halted
at a position 35' flush with the bolt face 36, so that it cannot discharge a cartridge
in the chamber. It would be necessary for the firing pin to travel an additional distance
forward before the tip 35 could protrude far enough from the bolt face to indent and
ignite the primer of a cartridge. Thus, even though the bolt has reached a fully-locked
condition at the stage shown in FIG. 4, still further forward travel of the bolt carrier
is required before the firearm can be discharged; this provides an additional margin
of safety to cover the possibility that the parts might become distorted or badly
worn.
[0023] In the position of FIG. 4, the carrier extension lies a distance I behind the bolt
shank 42. Additional forward movement of the carrier 28 through the distance I is
illustrated in FIG. 6. If the hammer is released at this stage, it will drive the
firing pin forward the distance L + I, causing the head to reach a position 48" abutting
against the bolt shank 42, and the tip to reach a position 35" protruding the distance
I beyond the bolt face 36. This is the maximum depth to which a cartridge primer can
be indented by the forward momentum of the firing pin.
[0024] The cam tracks 52 have straight lost-motion sections extending forwardly from their
curved sections at dwell distance D, as appears in FIGS. 4 and 6, to allow not only
the incremental forward movement I of the carrier 28 and action bars 22, but also
some additional movement into their extreme forward positions shown in FIG. 7. At
any point in this additional movement, the weapon may be fired by releasing the hammer,
which strikes the head of the firing pin as it reaches a position 66", in which it
is halted by contact the magazine 70. The momentum imparted to the firing pin 34 compresses
the spring 54, and drives the firing pin forwardly until its head strikes the bolt
shank 42 at the position 48", and its tip projects from the bolt face at the position
35" to discharge the firearm,
[0025] FIG. 8 illustrates the initiation of subsequent movements of the parts to reopen
the breech and recock the hammer. The action bars 22 are driven to the rear, as shown
by the arrow, by either manual or gas operation as the case may be. This initially
retracts only the bolt carrier 28, as its attached cam pins 50 pass through the straight
lost-motion portions of the cam slots 52. Then the cam pins pass into the curved portions
of the cam slots, rotating the bolt 30 to the unlocked position of FIG. 2. At the
illustrated stage, with the cams pins 50 at the rear ends of the slots 52, the rearward
movement of the action bars and bolt carrier is imparted to the bolt 30 as well.
[0026] During the rearward travel of the bolt carrier 28, its extension 46 pulls the firing
pin head 48 along with it, away from contact with the bolt shank 42. The head 48 soon
engages the hammer 66, and pushes it counterclockwise out of contact with the magazine
70. The completion of the counterclockwise hammer recocking motion is effected by
a subsequent engagement between the bottom of the bolt carrier and the hammer, until
the parts reach the position of FIG. 1, when the hammer is held cocked by the aforementioned
fire control.
[0027] In the preferred embodiment which has been illustrated and described, the rearward
extension 46 of the bolt carrier 28 is made even longer than is necessary to ensure
that the bolt lugs 40 must be fully locked to the barrel lugs 16 before the firing
pin tip 35 can be made to protrude from the bolt face 36 to discharge the weapon.
This provides a margin of extra safety in the event that the parts, particularly the
enlarged firing pin head or abutment 48 and the extension 46, might become worn or
distorted. This aspect of the invention can be more clearly understood by analyzing
the dimensional relationships of the parts in somewhat greater detail.
[0028] As appears in FIGS. 6 and 7, the length of the firing pin 34, between the forward
surface of the abutment 48 and the tip 35, is equal to the length of the bolt 30 plus
the maximum cartridge indent distance I, which is reached by the tip upon contact
of the abutment with the bolt shank 42. The extension 46, is of such a length that
after the bolt carrier has moved forwardly from the position of FIG. 1 to that of
FIG. 3 to close the bolt against the breech of the barrel 12, it holds the abutment
48 at a distance L + I to the rear of the bolt shank 42, and consequently holds the
firing pin tip at a distance L to the rear of the bolt face 36.
[0029] Movement of the bolt carrier farther forward a distance L, to the position of FIG.
4, causes the cam pins 50 to pass through the curved portions of the cam tracks 52,
whose longitudinal. length defines the distance L, and rotates the bolt to lock it
to the barrel. At this stage, the carrier extension 46 still lies to the rear of the
shank 42 a distance I, so that the abutment 48 can travel forwardly no more than the
distance L, only enough to bring the tip 35 flush with the bolt face. Still further
forward travel of the bolt carrier through the distance I, to the position of FIG.
6, is necessary to remove the block against contact between the abutment 48 and the
shank 42.
[0030] It will be seen from this analysis that if the extension 46 were to be shortened
by the length I, the full bolt lock-up condition shown in FIG. 4 would still have
to be achieved before the abutment 48 could contact the shank 42 and cause the tip
35 to protrude the distance I. If the extension 46 were to be shortened still more,
this protrusion of the firing pin could be permitted at some point during the locking
rotation of the bolt 30, when the lugs 40 and 16 were sufficiently engaged to insure
safety, but not fully interlocked as shown in FIGS. 4 and 5. Such variations are considered
to fall within the scope of the invention in its broader aspects, although they are
not preferred because of the lesser degree of safety they would provide in a firearm
that is intended to serve a useful life of indefinite length, and whose parts might
become worn or distorted after long use.
CLAIM 1. In a firearm of the type having a receiver; a barrel secured to said receiver
and having a rearwardly-open breech formed with locking lugs; a bolt carrier reciprocable
longitudinally in said receiver; a breech bolt having a front face adapted to close
said breech, said bolt being formed with locking lugs rotatably engageable with said
breech lugs to lock said bolt thereto, said bolt being received in said bolt carrier
in longitudinally and rotationally movable relation; a firing pin received in said
bolt for longitudinal sliding movement between a position retracted behind said face
and a position protruding therefrom; and cam means drivingly connecting said bolt
with said bolt carrier and constructed and arranged for effecting a forward longitudinal
movement of said bolt to close said face against said breech in response to a corresponding
forward movement of said bolt carrier, and for effecting rotary movement of said bolt
to a locked position interengaging said lugs in response to further forward movement
of said bolt carrier following arrest of forward movement of said bolt by closure
of said face against said breech;
the improvement comprising a firing pin block which includes an enlarged abutment
formed rearwardly on said firing pin, and a rearward extension of said bolt carrier;
said cam means being constructed and arranged to locate said rearward extension, in
all positions of said bolt other than said locked position, to block sufficient forward
movement of said enlarged abutment to enable said firing pin to move from said retracted
position into said position protruding from said bolt face.
CLAIM 2. A firing pin block as recited in CLAIM 1, said cam means being so constructed
and arranged that said rearward extension: engages said abutment to block any forward
movement of said firing pin throughout said corresponding forward movement of said
bolt carrier; moves forwardly with said bolt carrier during said further forward movement
thereof; and reaches a position to permit sufficient forward movement of said abutment
to enable said firing pin to move into said protruding position only after said further
forward movement is at least substantially completed.
CLAIM 3. A firing pin block as recited in CLAIM 1, in which said bolt, firing pin,
and bolt carrier are longitudinally movable parallel to a common axis; and said rearward
extension of said bolt carrier is aligned longitudinally of said common axis with
said enlarged abutment so that the extreme forward displacement of said firing pin
with respect to said bolt carrier is limited by engagement of said abutment with said
rearward extension.
CLAIM 4. A firing pin block as recited in CLAIM 3, in which said bolt has a rear shank
portion aligned longitudinally of said common axis with said enlarged abutment, and
the limit of forward displacement of said firing pin with respect to said bolt, into
said position protruding from said bolt face, is defined by engagement of said abutment
with said shank portion.
CLAIM 5. A firing pin block as recited in CLAIM 4, in which said cam means are constructed
and arranged to locate said rearward extension of said bolt carrier rearwardly from
said shank portion of said bolt to prevent engagement of said abutment with said shank
portion, in all longitudinal and rotational positions of said bolt other than said
locked position interengaging said lugs.
CLAIM 6. A firing pin block as recited in CLAIM 1, including means constructed and
arranged for preventing rotation of said bolt with respect to said bolt carrier during
said corresponding forward movement of said bolt carrier to close said face against
said breech, and for releasing said bolt for rotary movement by said cam means during
said further forward movement of said bolt carrier.
CLAIM 7. A firing pin block as recited in CLAIM 1, said cam means including a cam
slot having a circumferentially-curved portion extending longitudinally a fixed distance
L, such that said rotary movement of said bolt to a locked position is effected by
said further forward movement of said bolt carrier through said fixed distance L3
said rearward extension of said bolt carrier having a length such that, upon completion
of said corresponding forward movement of said bolt carrier to close said bolt face
against said breech, said rearward extension engages said enlarged abutment in said
retracted position of said firing pin to prevent forward movement of said firing pin;
and upon completion of said further forward movement of said bolt carrier to rotate
said bolt and interengage said lugs, said rearward extension terminates forward of
said abutment said distance L, whereby said extension limits forward movement of said
abutment and said firing pin to distance less than L until said further forward movement
of said bolt carrier is completed.
CLAIM 8. A firing pin block as recited in CLAIM 7, in which said firing pin extends
forwardly from said abutment thereof to a tip which, in said retracted position of
said firing pin, lies substantially said distance L behind said bolt face.
CLAIM 9. A firearm as recited in CLAIM 8, in which said bolt has a rear shank portion
engaged by said enlarged abutment in said protruding position of said firing pin;
said rearward extension being positioned at the completion of said corresponding forward
movement at a distance to the rear of said shank portion at least substantially as
great as said distance L.
CLAIM 10. A firearm as recited in CLAIM 9, in which said bolt has a rear shank portion
engaged by said enlarged abutment in said protruding position of said firing pin;
said cam means being constructed and arranged to permit additional forward lost motion
of said bolt carrier with respect to said bolt after completion of said further forward
movement; said rearward extension of said bolt carrier extending, at the completion
of said corresponding forward movement, to a distance to the rear of said shank portion,
exceeding said distance L by a distance I; said rearward extension being moved forwardly
by said further forward movement of said bolt carrier through said distance L and
thereby extending, at the completion of said further forward movement, said distance
I to the rear of said shank portion to prevent engagement of said abutment with said
shank portion;
whereby said bolt must first be fully locked, and at least a portion of said forward
lost motion of said bolt carrier must then be executed, to move said rearward extension
still farther forward through said distance I, before said abutment can contact said
shank portion and said firing pin can thereby reach said protruding position.