A device for sighting-in firearms is disclosed. The device comprises a telescope connected to a mandrel. The mandrel is sized to fit within a variety of calibers of gun bores. The mandrel has a tapered sleeve with a conical shape which centers the outside end of the sleeve in the outside end of the firearm bore. The inside end of the sleeve has a circumferentially expandable structure which allows the sleeve to be secured in the center of the bore when flared by the head of a slideable mandrel core. The telescope is connected to the mandrel with an optical arrangement through which the line of sight of the telescope is observable. The mandrel is constructed so that when the device is inserted in the bore of a firearm, the line of sight of the telescope is centered with and parallel to the axis of the mandrel, which is also the axis of the firearm bore.

BACKGROUND OF THE INVENTION 
This invention relates to devices for sighting in firearms, and more 
particularly to devices for accurately positioning the firearm sight to 
correspond to the point of impact of projectiles expelled from said 
firearms. 
Firearms are often equipped with sights which a person using the firearm 
uses to aim the firearm. The sights often comprise a telescope which 
allows the user a magnified view of his target. Such telescopes include 
reticles (cross hairs) observable while viewing a target through the 
telescope. The process of "sighting-in" the firearm consists of aligning 
the firearm sights, particularly the telescope cross hairs, so as to 
accurately correspond to the point of impact of projectiles fired from the 
firearm. 
Each caliber of firearm (and even similar calibers made by different 
manufacturers) and bullet muzzle velocity results in a different bullet 
trajectory. All trajectories are nearly parabolic due to gravity. Thus, 
firearms are generally sighted-in for the muzzle velocity and distance of 
bullet travel expected in actual use. For example, a hunter will sight in 
his particular caliber rifle for shooting a particular bullet at a 
particular distance. 
One method of sighting-in firearms is to shoot at the center of a target 
located at the desired distance. The point where the bullet actually 
strikes the target is noted, the firearm sights are adjusted, and the 
process is repeated until the desired accuracy is obtained. 
Various devices have been designed to aid in sighting-in firearms. For 
example, U.S. Pat. No. 1,295,075 to Sheppard discloses a bore sighting 
device which mounts in the end of a firearm bore and sets up a line of 
sight parallel with the axis of the bore mounting segment of the device. 
Likewise, U.S. Pat. No. 3,112,567 to Flanagan describes a device mountable 
in the end of a rifle which includes marks to which the rifle telescope 
can be adjusted depending on the expected target distance. U.S. Pat. No. 
3,744,133 to Fukushima discloses a collimating device which has a conical 
surface to center the device in various calibers of firearms. U.S. Pat. 
No. 4,090,305 to Cassidy also discloses a device to be mounted in the end 
of a gun barrel in an aid to sighting-in the sights on the gun. 
One common problem with all of the above devices is that when used, the 
firearm is sighted-in on a device at the end of the barrel, only a foot or 
two at most from the gun sights. Therefore, any slight error made while 
sighting-in using the device will be greatly magnified when shooting at a 
target several hundred yards away. Even if the precision of alignment were 
.+-.0.01 inches for a device mounted 2 feet from the guns telescope, at 
300 yards the precision would be .+-.4.5 inches, or about a 10 inch 
diameter circle, Thus, these types of prior art devices are typically used 
only as a first approximation, and actual target shooting is required to 
sight the firearm in with the desired degree of accuracy. 
German Patentschrift No. 647,136 describes a device for checking the 
accuracy of the sighting mechanism of a gun. The device uses a prismatic 
telescope in an optical arrangement designed to view along the axis of 
bore to check the accuracy of the gun sighting device. A problem common to 
the disclosed device and the previously discussed devices is the lack of 
accuracy in lining up the device itself with the axis of the firearm bore. 
In the case of the German reference, the optical device is mounted in the 
bore of the gun on a mandrel which includes two spherical bearing 
surfaces. In order that such a mandrel could be inserted into and removed 
from the bore, there must be sufficient clearance between the inside of 
the bore and the bearing surfaces to allow such placement without harm to 
the inside of the bore. Any freeplay between the mandrel and bore will 
result in a slight angle between the axis of the bore and the axis of the 
optical arrangement mounted on the mandrel. The small moment of error thus 
present will affect the accuracy to which the gun can be sighted-in. 
Another disadvantage is that a separate mandrel must be used for each 
caliber. 
The devices disclosed in the Cassidy and Fukushima et al. patents use a 
compressible member to expand within the bore in an attempt to hold the 
devices in line with the axis of the bore. The nature of the expandable 
means used, however, makes it very difficult to insure exact centering. 
The device disclosed in the Flanagan patent is mounted only at the mouth 
of the bore. 
SUMMARY OF THE INVENTION 
The device of the present invention comprises a telescope connected to a 
mandrel, the mandrel being sized to be insertable within a variety of 
calibers of gun bores. The mandrel has a tapered sleeve which at the 
outside end is conically shaped to center the outside end in the end of 
the bore. The inside end of the sleeve has an expandable means. Inside the 
sleeve is a slideable mandrel core, including a flared head at the inside 
end. Means for sliding the core are provided which cause the inside end of 
the mandrel sleeve to expand and securely center the mandrel in the bore. 
The telescope is connected to the mandrel with an optical arrangement 
through which the line of sight of the telescope is observable. 
The present invention provides a mandrel which securely centers the 
sight-in device within the axis of the firearm bore. Using the device it 
is possible to sight-in a firearm without firing repeated shots. 
The device of the present invention is useful in sighting-in a wide variety 
of calibers of firearms, giving the device a wider range of usage than a 
device sized for one caliber or a narrow range of firearm calibers. 
Further aspects and advantages of the invention will be best under stood in 
view of the detailed description of the invention and the drawings, a 
brief description of which follows.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PREFERRED EMBODIMENT OF THE 
INVENTION 
FIG. 1 shows the preferred embodiment of the present invention mounted in 
the barrel 15 of a rifle 10. The sight-in device 20 is useful in 
sighting-in rifles, pistols, and any firearm which includes sights for 
accurately aiming the firearm. The device will be most useful, of course, 
when the sights on the firearm provide a high degree of accuracy in 
aiming, such as the telescope 14. As used herein, the term "sight-in" 
refers both to the initial accuracy adjustment of a firearm's sight and 
also to checking the accuracy of a firearm which has previously had its 
sights accurately adjusted. 
As shown in FIG. 2, the sight-in device 20 comprises three major sections, 
a mandrel 30, a housing 50 and a telescope 70. The mandrel 30 comprises a 
mandrel sleeve 32 and mandrel core 40, best shown in FIG. 3. The sleeve is 
tapered so that its outside diameter narrows going from the outside end to 
the end inside the bore 17 of the rifle barrel 15. This taper allows the 
mandrel 30 to be centered in the bores of a wide variety of calibers, such 
as bores ranging in caliber from about 0.25 inches to 0.40 inches. Of 
course, other sizes of mandrel sleeves may be constructed for bores 
outside this range. 
The taper must be narrow enough so that the sleeve 32 centers on the 
outside end 18 of the bore 17 and not the chamfer 19 normally found at the 
end of most barrels. This is because the chamfer 19 may not be concentric 
with the bore 17. On the other hand, the larger the taper, the greater 
variety of bores the mandrel will fit without being of an excessive 
length. A range of 1.degree. to 10.degree. is preferred on the taper of 
the sleeve, with a 2.degree. taper being the most preferred. 
On its inside end, the sleeve 32 includes four longitudinal slots 34, 
leaving four fingers 36 in between. See FIGS. 4 and 5. In addition, the 
inside diameter of the sleeve 32 at the inside end is tapered, getting 
thinner towards the inside end of the sleeve. See FIG. 3. The sleeve 32 on 
its extreme outside end is attached to the housing 50 by a threaded nipple 
38. 
Slideably mounted inside sleeve 32 is the mandrel core 40. The core 40 
includes a flared head 42 on the inside end. The flared head 42 has a 
conical outside shape substantially the same as the inside diameter taper 
of the fingers 36. The core 40 is longer than the sleeve 32, extending 
into the housing 50. This end of the core 40 includes threads 44 onto 
which a nut 46 is secured. The nut 46 includes a shoulder 48. 
Surrounding the nut 46 and bearing against shoulder 48 is a spring 52. The 
nipple 38 is hollow over most of its length, allowing the spring 52 to fit 
within the nipple 38 and surround nut 46 and the threaded portion of core 
44. The natural tendency of spring 52 is to bias the flared head 42 of the 
core 40 against the fingers 36 of the sleeve 32. 
The shape of the flared head 42 causes the fingers 36 to spread apart. Thus 
the fingers and slots form a circumferential expandable means at the 
inside end of the mandrel sleeve 32. When expanded, the inside end of the 
sleeve 32 engages the bore 17 and secures the inside end of the mandrel 30 
in the center of the bore 17. The mandrel 30, when in this position, is 
secured at two points inside the bore 17 of the firearm, aligning the axis 
of the mandrel sleeve 32 with the axis of the bore 17. 
The housing 50 includes a body 57 providing the physical structure to 
connect the mandrel 30 with the telescope 70. The housing 50 also includes 
several other components which allow for mechanical actuation of the 
mandrel core 40 and provide an optical arrangement through which to view 
the line of sight through the telescope 70. As seen in FIG. 4, a lever 54 
is connected to a cam 56 journaled in the housing body 57. The cam is 
cylindrical in shape except for a flattened area 58. In the position 
depicted in FIG. 4, the flattened area 58 is aligned with the nut 46, 
allowing the spring 52 to force the flared head 42 of the mandrel core 40 
as far as possible into the sleeve 32. Turning the lever 54 through 
90.degree. or more rotates the cam 56 so that the nut 46 compresses the 
spring 52 and slides the core 40 further into the bore 17. As a result, 
the flared head 42 disengages the fingers 36, allowing the expanded inside 
end of the mandrel sleeve 32 to return to its normal shape. In this 
position, the mandrel 30 may be removed from or inserted into the bore 17. 
Appropriate stops (not shown) are provided on he housing 50 to control the 
angle through which the lever 54 may be turned. 
The optical arrangement inside the housing 50 includes a flat mirror 60 
mounted at a 45.degree. angle with respect to the axis of mandrel 30. The 
top of the housing 50 includes a hole and an eyepiece 62 through which 
reflections off the mirror 60 may be viewed. 
The optical arrangement of the telescope 70 is not critical to the present 
invention, and any suitable telescope may be used. A preferred telescope 
is the Leopold M8-6x compact rifle scope. The housing on the telescope 70 
is modified to provide a threaded nipple 72 which screws into the housing 
body 57. By looking through eyepiece 62, the line of sight, including the 
reticle, of the telescope 70 may be viewed as it reflects off mirror 60. 
To use the device 20 to adjust the sights of a firearm, the device 20 
itself must be first calibrated for the caliber of firearm for which it 
will be used. To do this, the device 20 is first secured in the bore 17 of 
the firearm using the lever 54 as previously described. The firearm is 
then placed on a steady surface and positioned so that the line of sight 
of the device 20 as viewed through he eyepiece 62 intersects an aim point. 
Without disturbing the firearm, the firearm sights are adjusted to also 
line up on the aim point. If the firearm is accidently moved during this 
step, several repetitions of positioning the firearm and adjusting its 
sights may be necessary in order to get the line of sight of the device 20 
and the firearm sights to intersect on the aim point. 
Next, the device 20 is removed from the firearm. A single shot is then 
fired at a target the distance away at which the firearm is being 
sighted-in (for example, 200 yards) using the sights of the firearm to aim 
at the target. The firearm should be held very steady while this shot is 
fired. 
The device 20 is again secured in the bore 17 of the firearm, and the 
firearm positioned so that the line of sight of the device 20 intersects 
the target. The firearm sights are then adjusted to intersect the hole 
made by the bullet fired in the previous step. When the firearm sights and 
line of sight of the device 20 line up, at the same time, with the bullet 
hole and the target respectively, the firearm is sighted in. 
One further step allows the device 20 to be used later to verify that the 
firearm is still sighted in. While the firearm is still positioned so that 
the firearm sights are in line with the bullet hole, the adjustments 80 
(FIG. 2) on the telescope 70 of the device are adjusted so that the line 
of sight of the telescope 70 also intersect the bullet hole. 
After this procedure, the device 20 can be used to verify that the sights 
on the firearm are correct. For example, after long periods of disuse, or 
after the sights have been bumped or replaced, the sights on the firearm 
can be accurately adjusted without firing a shot by inserting the 
calibrated device 20 into the bore of the firearm and adjusting the sights 
of the firearm to align with the line of sight of the device 20 at the 
desired sight-in distance. Since this verification or sighting-in is 
performed without firing a shot, it is possible to sight in the firearm in 
situations where traditional sighting-in procedures are not practical. 
It has been found that once the device 20 has been calibrated for a given 
firearm, it can be used to adjust or verify the sights on firearms 
shooting bullets which have trajectories similar to the trajectory for 
which the device 20 was calibrated. Of course, if the trajectory is 
significantly different (either because a different muzzle velocity or 
caliber bullet is used), greater accuracy can be achieved for sighting-in 
the new firearm by first recalibrating the device for the new trajectory. 
However, when the differences in bullet trajectories is relatively small 
(as is most often the case), the calibrated device 20 may be used to quite 
accurately sight in a variety of firearms without the need for 
recalibration. The method of mounting the mandrel 30 in the bore 17 and 
the internal alignment between the mandrel 30 and telescope 70 of the 
device 20 provide a high degree of accuracy which more than compensates 
for small differences in trajectories, as compared to the limits of 
accuracy provided by prior art devices. 
In the preferred embodiment, the mandrel sleeve is approximately 4 inches 
long. A longer sleeve is preferred if the range of calibers to be sighted 
in is fairly narrow. The tapered end of the mandrel core is bronze. The 
housing 50 and mandrel 30 are made of aluminum to be light weight. As 
shown in FIG. 5, the slots 34 are made in the sleeve 32 so that a finger 
36, rather than a slot 34, is at the top (12 o'clock) position. In this 
manner, the weight of the device 20 acts directly against a metallic 
surface, which helps make sure the inside end of the mandrel 30 remains 
centered. 
In order to achieve the best alignment, it has been found that the sleeve 
32 and housing 50 should be constructed from the inside out. Thus, to make 
the sleeve 32, a piece of stock material is first drilled through. Then 
the stock is turned to the proper outside dimensions while centered about 
this initial bore. The threaded nipple 38 and tapered inside end are also 
machined while the stock rotates about this inside hole. Likewise, the 
holes into which the telescope 70 and mandrel 30 screw into the housing 
body 57 are made from a common centerline. 
In a less preferred embodiment, the telescope 70 may be mounted on a 
bracket which is attached to the mandrel and which supports the telescope 
from its bottom using traditional telescope mounts. If the bracket is not 
shaped so as to center the telescopic line of sight with the bore axis, 
the offset distance must be accounted for in the final sight-in 
adjustments. 
From the foregoing it will be evident that the device of the present 
invention makes it possible to accurately and quickly sight-in a firearm. 
Once the device 20 has been calibrated for the desired trajectory, firearm 
shooting bullets of similar trajectories can be sighted in without firing 
a shot. This reduces the danger associated with sighting-in a firearm, 
makes it possible to sight-in at night (using a light as the "target") or 
in an area such as around a hunting camp where noise is undesirable, and 
saves on costly ammunition otherwise used during the sighting-in process. 
Also, the device can be used to check the accuracy of the sights on a 
firearm previously sighted-in, or determine if the line of sight through a 
variable power telescope changes as the magnification factor is changed. 
The design of the mandrel 30 provides a sure, center alignment of the 
device 20 with the bore 17 of a variety of calibers of firearms. The 
actuating system including the lever 54, cam 58, slideable core 40 and 
flared head 42, provide an easily operated mechanism to cooperate with the 
mandrel 30 to quickly insert and secure or remove the device 20 in or from 
the firearms being sighted-in. 
The presently preferred embodiment of the invention has been described and 
given as an illustrative example. Since numerous modifications and changes 
may be made without departing from the invention, it is not desired to 
limit the invention to the exact construction and operation shown. 
Accordingly, all suitable modifications and equivalents may be resorted to 
without departing from the present invention, the scope of which is 
defined by the following claims.