Hand gun with improved barrel mounting pin

The frame of a hand pistol has in its forward end a pair of spaced furcations between which the lug on a removable gun barrel is pivotally mounted by means of an adjustable mounting pin, which permits the barrel to be pivoted between an open or loading position, and a closed or firing position. The adjustable pin comprises an Allen-head screw having a cylindrical head positioned snugly in a circular bore formed in one furcation, and a reduced-diameter, externally-threaded shank, which extends coaxially through a bore in the barrel lug, and which is threaded into an annular nut that is positioned snugly in a registering bore in the other furcation. One or more radially expansible sleeves surround the reduced-diameter shank of the screw of the bore of the barrel lug, and are designed so that when the nut is threaded toward the head of the screw, the sleeve or sleeves expand slightly radially, if necessary, to take up any undesirable slack which might otherwise exist as between the frame and the removable barrel, thus increasing the accuracy of the gun and minimizing its head spacing. Either a single sleeve having therein one or more longitudinally extending slots can be used; or a series of sleeves, the confronting ends of which have sliding engagement along a plane inclined to the axis of the screw, can be employed.

This invention relates to hand guns, and more particularly to hand guns of 
the type having replaceable barrels, which are releasably attached by 
removable mounting pins to the gun frames. Even more particularly, this 
invention relates to an improved mounting pin for accurately securing 
barrels of the type described to their associated gun frames. 
Competitive target shooting with hand guns requires the use of an extremely 
accurate firearm. One such event which has become extremely popular in 
recent years involves the use of metallic targets that are designed to be 
struck and knocked over by bullets fired from hand guns. Typically, 
several series of such targets are employed, starting with a series of 
relatively small targets placed at close range, and progressing to a 
series of extremely heavy targets at long range. Although a competitor 
must use the same gun throughout a given match, different guns may be used 
for different matches. As a consequence, guns having replaceable barrels 
have become popular because they give a competitor the option to choose 
any one of a number of different barrels for a given match. 
For example, Thomson: Center Arms of Rochester, New Hampshire manufactures 
a hunting and/or target practice hand gun the frame of which is designed 
to accommodate any one of a plurality of differently sized gun barrels, so 
that the same gun can be used to fire multicaliber bullets. A gun of this 
type therefore, is particularly suited for use in competition involving 
the above-noted metallic target meets, because a new or different barrel 
can be readily substituted each time a different caliber is desired for 
use in any particular match. 
One of the major difficulties heretofore encountered in connection with 
hand guns of the type described is that the accuracy of the gun tends to 
vary rather considerably from barrel to barrel. In the case of one such 
prior gun, for example, each replaceable barrel has a lug projecting from 
its underside adjacent its breech section; and this lug is pivotally 
connected by a cylindrical mounting pin between the legs of a furcation 
which is formed on a forward end of the associated gun frame. When thus 
attached to the gun frame, the barrel is pivotal into and out of a locked 
position in which its bore registers properly with the firing pin which 
reciprocates in the frame forwardly of the hammer. With this type of 
mounting it has been discovered that the accuracy of the gun is changed 
each time the gun barrel is changed or replaced. 
Not only is the accuracy of the above-noted gun inconsistent, but also its 
head spacing (the space between the rear end of the barrel and the 
confronting surface on the gun frame) tends to vary considerably from 
barrel to barrel. Ideally this head space is held to a minimum to prevent 
any undesirable expansion of the brass casing of a bullet or shell during 
the firing of a gun. Since most competitors reload and use such shell 
casings over and over again, it is desirable to minimize any such 
expansion of the shell casings, because this in turn reduces the need for 
working the brass casings when they are resized during the reloading 
process, and consequently prolongs the useful life of a casing. Moreover, 
with minimum head space the likelihood of any undesirable separation or 
splitting of a shell casing is minimized. 
Accordingly, it is an object of this invention to provide improved means of 
releasably mounting replaceable gun barrels on the frames of hand guns of 
the type described, thereby to improve the reliability of the guns by 
eliminating variations in their accuracy from barrel to barrel. 
Another object of this invention is to provide for hand guns of the type 
described improved barrel mounting means which minimizes the existence of 
undesirable head spacing in the guns. 
A more specific object of this invention is to provide an improved, 
adjustable mounting pin for pivotably attaching replaceable gun barrels to 
the frames of hand guns of the type described. 
Still another object of this invention is to provide an improved mounting 
pin of the type described which can be adjusted accurately and securely to 
mount each of a plurality of different gun barrels on the same frame of a 
hand gun so as to increase the accuracy of the gun, and to reduce the head 
space thereof, as compared to prior such guns. 
Other objects of the invention will be apparent hereinafter from the 
specification and from the recital of the appended claims, particularly 
when read in conjunction with the accompanying drawings.

Referring now to the drawings by numerals of reference, and first to FIGS. 
1 and 2, 10 denotes generally the frame of a pistol frequently employed in 
metallic target competitions of the type noted above. The frame 10 has the 
usual hand grip section 11, a trigger guard 12 for the trigger 13, and a 
pivotal hammer 14, the operation of which forms no part of this invention. 
On its forward end frame 10 has two, spaced, parallel, upstanding legs or 
furcations 16, (FIG. 2) which form in the frame forwardly in the hammer 14 
an elongate slot or groove 17 (FIG. 2) for a purpose noted hereinafter. 
The two furcations 16 have therein a pair of registering, circular 
openings 18, which are equal in diameter, and which open on opposite 
sides, respectively, of the slot 17. 
Releasably attached adjacent its rear end to the forward end of the gun 
frame 10 by a novel mounting pin 20 is a conventional gun barrel 21. 
Barrel 21 is one of several different types of barrels which are adapted 
to be attached releasably to frame 10 by means of an integral lug 22, 
which projects from the underside of each such barrel adjacent its rear or 
left end as shown in FIG. 1. Each such lug 22 has a pair of spaced 
parallel sidewalls which are separated a distance approximately equal to 
the space between the frame legs 16, so that each lug 22 will fit snugly 
and movably between the legs 16 as noted hereinafter. Moreover, each such 
lug 22 has therethrough a circular bore 23 (FIG. 2) the axis which extends 
right angles to, and transversely between, the opposed side walls of the 
lug so as to be registerable coaxially with the openings 18 in the frame 
legs 16, as shown in FIG. 2. Also as will be apparent from FIG. 2, the 
diameters of the registering openings 18 and 23 are substantially equal. 
Heretofore it was customary to secure the lug 22 of a barrel 21 between the 
frame legs 16 by means of a solid, cylindrical mounting pin (not 
illustrated), which was removably inserted into and which extended snugly 
through, the registering bores 18 and 23. When mounted in this manner the 
associated gun barrel 21 was then pivotal from its open position (FIG. 1) 
to a closed position (not illustrated) in which its rear end was latched 
by known means in a firing position with the rear end of its bore disposed 
in registery with the firing pin of the gun. The gun could then be cocked 
and fired, after which the barrel latching means was released manually in 
a known manner, so as to enable pivotal movement of the barrel 21 back to 
its open position. Because of the variations in the sizes and positions of 
the bores 23 in the mounting lugs 22 on different barrels 21, prior or 
conventional mounting pins have resulted in the above-noted unsatisfactory 
accuracy from barrel to barrel, and the inconsistent head spacing. 
Referring now to FIG. 2, the improved mounting pin 20 which obviates the 
above-noted disadvantages of conventional mounting pins, comprises a flat, 
Allen-head cap screw 30 having a cylindrical head 31, an integral, 
reduced-diameter, externally-threaded shank 32, and a truncated-conical 
shoulder section 33 formed at the juncture of its head and shank sections. 
The screw 30 has an overall length approximately equal to the distance 
between the outside surfaces of the frame legs 16, and has plane, 
transverse end surfaces which, in use, are disposed approximately coplanar 
with the outer surfaces of the frame legs 16 so as not to interfere with 
the removable front stock (not illustrated) of the gun. Head 31 of the 
screw, which has in its outer end the usual recess 35 for accommodating 
the end of an Allen wrench, fits snugly and slidably in an opening 18 in 
one of the frame legs 16. 
Adjustably threaded onto the shank 32 of the screw 30 in the bore 18 of the 
other frame leg 16 is an annular nut 37, the outside diameter which also 
is approximately equal to the diameter of the bore 18 in which it is 
positioned. The nut 37 has formed on its inner end a beveled surface 36 
which is similar to, but inclined oppositely to, the truncated-conical 
shoulder 33 on screw 30. The nut 37 has a castellated outer end containing 
four, equiangularly spaced notches 38 (only three of which are shown in 
FIG. 2) for accommodating the forked head of a conventional tool, which 
can be employed to hold the nut 37 against rotation during its adjustment 
of screw 30 as noted hereinafter. 
Mounted in the bore 23 of the barrel lug 22, and surrounding the part of 
the screw shank 32 that extends between the frame legs 16, is a split 
sleeve or ring 41, which is made from a piece of hardened, precision 
machined steel, or the like. Ring 41 has in its annular wall a 
longitudinally extending slot 42, which extends continuously between 
opposite ends of the ring to enable radial expansion thereof. Also, 
opposite ends of the ring 41 are countersunk or otherwise machined to form 
on opposite ends of its bore wall beveled or truncated-conical surfaces 
44, which are engagable, respectively, with the inclined shoulder 33 on 
the screw 30, and with the tapered surface 36 formed on the inner end of 
nut 37. Also as shown more clearly in FIG. 2, the overall length of the 
ring 41 is such that it can be positioned entirely within the bore 23 of 
the barrel lug 22, and therefore does not project axially into either bore 
18 in the frame legs 16. 
In order to remove barrel 12, it is first pivoted to its open position, 
(FIG. 1), and the nut 37 is then backed off or adjusted toward the right 
on the screw shank 32 in order to release any axial pressure which may be 
exerted against opposite ends of ring 41 by screw head 31 and nut 37. This 
enables the ring 41 to contract radially until its outer diameter is, in 
practice, approximately equal to the diameter of the bore 23 in the barrel 
lug. 22. At this time the pin 20 can then be readily removed from the 
bores 18 and 23 merely by tapping one end or the other of the pin. After 
it has been removed, and assuming that it is desirable to replace the 
existing gun barrel, a second gun barrel having a lug 22 is mounted on the 
frame 10 so that the bore 23 in its lug 22 registers approximately with 
the openings 18 in the frame furcations 16. The pin 20 is then reinserted 
into the registering bores 18 and 23 until it assumes approximately the 
position as shown in FIG. 2, wherein opposite ends of the pin register 
approximately with the outer surfaces of the frame legs 16. At this time 
the pin 20 can be adjusted by rotating screw 30 relative to nut 37 (or 
vice versa) to cause the split ring 41 to expand slightly in a radial 
direction in order to take up any undesirable play that might exist in the 
bore 23 of the new barrel lug. This adjustment causes the nut 37 to be 
drawn, by way of example, axially toward the left on the screw shank 32 as 
shown in FIG. 2, thereby causing the inclined surfaces 33 and 36 on the 
screw 30 and nut 37, respectively, to exert equal and opposite forces 
against opposite ends of the split ring 41. The split ring therefore tends 
to expand radially, as permitted by the slot 42 in the ring, thereby 
increasing the diameter of the ring until its outer peripheral surface 
snugly engages against the bore wall 23 of the barrel lug 22. 
This expansion of ring 41 does not interfere in any way with the ability of 
the barrel 21 to be pivoted between its open and closed positions. This 
type of adjustment, however, does have the beneficial effect of taking up 
any undesirable slack which might otherwise occur in the mounting as 
between a frame 10 and a new gun barrel 21. Likewise this adjustment tends 
to reduce the amount of head space in the gun thereby not only increasing 
its accuracy, as noted above, but also prolonging the life of shell 
casings that are employed in the gun. 
In the example illustrated the tapered, mating surfaces 33, 36, and 44 on 
the screw 30, the nut 37 and the split ring 41, respectively, are formed 
at an acute angle to the axis of the pin 20, and by way of example, at an 
angle of approximately 30.degree. or 45.degree.. Obviously, however, the 
degree of inclination of these contacting surfaces can be varied slightly 
without departing from this invention. 
Referring now to the modified pin shown in FIG. 3, wherein like numerals 
are employed denote elements similar to those employed in the first 
embodiment, 50 denotes a flat, Allen-head type of screw having a 
cylindrical head 51, and a reduced-diameter, externally threaded shank 
section 52. In this embodiment the juncture between the head and shank 
sections of the screw is defined by a plane, transverse surface 53, which 
lies in a plane that extends at right angles to the axis of the screw. 
Also unlike the first embodiment, the castellated nut 57 in this 
embodiment has four, tool-accommodating notches 58 in its outer end, but 
has a plane, transverse inner end or surface 56, which extends parallel to 
the plane surface 53 on the head 51 of the screw. As shown more clearly in 
FIG. 3, these plane surfaces 53 and 56 are disposed to be in approximately 
coplanar registry with the inside surfaces of the frame legs 16, when the 
barrel 21 is mounted as shown in FIG. 3. 
In this second embodiment three, separate ring members 61, 62 and 63 are 
mounted in the bore 23 of the barrel lug 22 to surround the portion of the 
screw shank 52 which extends between the frame legs 16. Each ring 61, 62 
and 63 extends without interruption around a portion of the screw shank 
52; and the outer ends of the two outer rings 61 and 63 have formed 
thereon plane surfaces which are disposed to have coplanar registery with 
the plane surfaces 53 and 56 on the screw head 51 and the nut 57, 
respectively. However, opposite ends of the inner ring 62, and the 
confronting, inner ends of the outer rings 61 and 63, are plane surfaces 
which are inclined at an angle, for example approximately 60.degree., to 
the axis to the screw shank 52. As a consequence, the confronting ends of 
the rings 61 and 62 lie in a plane 65 (FIG. 3) inclined in one direction 
to the axis of the pin 50, while the confronting, coplanar surfaces of the 
rings 62 and 63 engage each other along a plane 66 (FIG. 3), which is 
inclined in the opposite direction relative to plane 65. 
As the result of the construction illustrated in FIG. 3, when the nut 57 is 
rotated to cause its advance toward the head on the screw 50, the axial 
pressure exerted on the outer ends of the rings 61 and 63 cause the 
confronting surfaces on the three rings to slide slightly relatively to 
one another, and in turn cause ring 62, for example, to be shifted 
slightly radially outwardly from the axis of the shank 52 relative to the 
rings 61 and 63. It has been found that this construction also results in 
more uniform accuracy and smaller head clearance in guns of the type 
described. 
In the embodiment shown in FIG. 4, 70 denotes an Allen-head screw having a 
modified head section 71, and a reduced-diameter, externally-threaded 
shank section 72. In this embodiment the inner end of head 71 has formed 
thereon a truncated-conical surface 73, which seats against a 
correspondingly inclined surface formed on one end of an annular washer 
74, which surrounds the screw 70 at the juncture of its head 71 and shank 
72. 
In this embodiment (FIG. 4), two annular members 75 and 76 surround the 
screw shank 72 between the legs 16 of the frame, and are held thereon by a 
nut 77 similar to the nut 57 shown in FIG. 3. The outer ends, 
respectively, of members 75 and 76 lie in transverse planes which nearly 
are coplanar with the inner surfaces of the frame legs 16. The inner ends 
of the annular members 75 and 76, however, comprise plane, inclined 
surfaces which engage each other so at 78 along a transverse plane which 
is inclined at approximately 45.degree. to the axis of the shank 72. As a 
consequence, when the nut 77 in this embodiment is tightened, the axial 
pressure placed against the outer ends of members 75 and 76 cause them to 
shift slightly radially in opposite directions relative to each other 
along the juncture 78, thereby taking up any slack which might otherwise 
exist as between the associated barrel 21 and frame 10. 
The embodiment shown in FIG. 5 illustrates a modified pin in which the 
Allen-head screw 80 and the associated nut 37 are identical to those 
employed in the first embodiment. The screw, therefore, has a cylindrical 
head 31 and a threaded shank 32 connected by a truncated-conical shoulder 
section 33. In this embodiment, the screw shank between frame legs 16 is 
surrounded by a modified ring or member 81 having in diametrally opposite 
sides thereof a first pair of registering, longitudinally extending slots 
82 (only one of which is shown in FIG. 5), which extend part way in from 
the right end of ring 81, and a second pair of registering, longitudinally 
extending slots 83, which are positioned at 90.degree. intervals from the 
slots 82, and which extend part way in from the left end of member 81. 
Slots 82 therefore form on the left end of ring 81 two, diametrally 
opposed portions 85, which support substantially the upper half of member 
81 in cantilever fashion from the lower half thereof, while the other two 
slots 83 leave portions 86 at diametrally opposite sides of member 81 
adjacent the right end thereof, for supporting two other opposed sections 
of the member 81 in cantilever fashion about the respective portions 86 of 
the member. 
Also as shown in FIG. 5 opposite ends of the bore in member 81 have formed 
thereon beveled surfaces 89 which are engagable by the complimentarily 
inclined surfaces on the inner end of the screw head 31 the nut 37, 
respectively. It will be apparent, therefore, that as the nut 37 is 
threaded onto the shank section 32 of this screw, the inclined surfaces on 
the inner ends of the head 31 and the nut 37 will cause portions of the 
ring member 81 to be expanded radially, and snugly into engagement with 
the bore 23 on the barrel lug 22. As in the case of the preceeding 
embodiments, the adjustable pin 80 thus permits the take-up of any 
undesirable slack which might otherwise exist between the barrel 21 and 
the frame to which it is attached. 
From the foregoing, it will be apparent that this invention provides a 
relatively simple and inexpensive means for dramatically increasing the 
accuracy of hand guns of the type described. Moreover, by proper 
adjustment of the novel mounting pins disclosed herein it is possible also 
to minimize the amount of head clearance in each such gun, thereby to 
prolong the life of the associated cartridges or gun shells that are used. 
Still another advantage of this type of mounting pin is that it can be 
readily adjusted and/or removed through the use of simple hand tools, such 
as for example, an Allen wrench, and a conventional tool of the type which 
is employed for operating castellated nuts. Of course, while in the 
illustrated embodiments the use of an Allen-head screws and castellated 
nuts has been suggested, it will be apparent to one skilled in the art 
that modifications of such screws and nuts can be employed without 
departing from this invention. Moreover, while only certain embodiments of 
the invention have been illustrated and described in detail herein, it 
will be apparent that this application is intended to cover any such 
further modifications thereof that may fall in the scope of one skilled in 
the art or the appended claims.