Lyman M77 Globe Sight

Most of us have an eclectic accumulation of stuff we have collected over the years based on our hobbies, professions, or even inheritance. In my case I have several genres of things, including obscure marine hardware, various woodworking novelties, motors, and, of course, gun parts. The gun parts represent several generations of meticulous acquisition and preservation, resulting in many items that are beautifully manufactured but sometimes missing critical parts or related assemblies.

Such was the case when I began a project to build a target plinker from a 1895 Mauser action I picked up at a gun show years back. The sight combination I selected for this project is comprised of a Lyman M77 front globe sight and Armstrong dual-range peep sight for the receiver. The rear sight is an early version of an Armstrong dual-range peep sight which is designed to mount on the right side of the receiver, a necessary requirement given the bolt-release lever on the left side of Mauser rifles.

The sight mounts to the receiver with a V-block base and two screws. The base is a snug fit between the bolt handle and rear of the ejector port, requiring precise measurements when drilling the holes in the receiver. The Armstrong sight includes several ingenious features, including knurled adjustment knobs for elevation and windage adjustments. These knobs have 40 pitch threads and detents every 30 degrees resulting in a mere 0.002" of movement per click.

Vernier scales are mounted on both axes, with graduation markings every 15 clicks. The sight mounts to the base by means of a vertical dovetail with a quick release button to disengage the elevation screw from the base. This permits the intricate portion of the sight to be removed for safe transport. The aperture screws into a small plate that rides in vertical channels on across feed block positioned by the windage screw. The aperture plate has two small springs on the bottom that bias the aperture up.

The "dual-range" feature is enabled by across bar above the plate. The cross bar has a V-notch on one side. When the bar is pushed so that the V-notch section is above the aperture plate the sight will rise approximately 0.040". A quick ballistic calculation using a nominal 170 grain bullet load indicates this "dual-range" roughly corresponds to the bullet drop between a 25-yard sight-in range and a 200-yard target.

I admit to being skeptical about the value of this "dual-range" capability, but the mechanism and machining is clever. The adjustment knobs, peep sight plate, vertical dovetail, and cross slide have locking screws with hex heads. A vertical stop screw with the same hex head size can be adjusted to prevent the sight from being lowered onto the top of the receiver. A small hex wrench accompanies the sight in a snug fitting hole at the top rear of the sight mount.

My Lyman M77 front globe sight has a female dovetail from front to rear, locked in place by a shoulder on a knurled screw mounted on the right side. More modern configurations like the Lyman Model 17 globe sight use a standard female dovetail cut across the top of the barrel and come with a variety of offsets.

Like the more modern M17 sight, the M77 includes a set of inserts, four sizes of apertures in a post-mounted ring (sometimes referred to as a "lollipop sight"), several colored solid inserts with a small aperture, and a poststyle insert. The inserts are placed

into the sight from the rear and held in place by a threaded cylindrical tube which serves as the rear cover for the sight. The sight body has milled slots on either side from the rear to middle of the sight that guides horizontal tabs protruding from the outside of the inserts. The inserts are made from a dull black metal sheet approximately 0.025" in thickness, except for the solid semi-translucent colored inserts, which are either yellow or red.

My M77 only had one insert remaining (an aperture with a 0.085 internal diameter) and no male dovetail to mount to the barrel. The inserts for this model can still be found, although in many cases the sets are not complete and exhibit some surface damage. While Lyman M17 inserts are compatible with the older M77 sight, other inserts, including those of the Lyman Series 20 and 93 globe sights, will not fit. This struck me as an opportunity to use a 3D printer to produce the inserts.

The first step was to model the sight in On Shape (OnShape.com), a free online Computer Aided Design (CAD) package. I made a parametric model for the inserts, which allows key variables such as the aperture size and sight style to be easily changed so that all the different sights can be generated. Additionally, custom configurations can be easily created by adjusting the variables. A complete set of inserts was modeled and exported to STL files, a file format native to the stereolithography CAD

software. The STL file format is a three-dimensional representation of the part’s surface geometry and can be used to view the part using a 3D viewing program and to create the physical object with a 3D printer. A set of six inserts was printed on a Dremel 3D45 printer using black PLA material—Polyactic Acid, a thermoplastic made from renewable resources. This material produces a flat black finish which is ideal for this application. Additional solid aperture sights were printed in red and yellow.

PLA is non-toxic; in fact, it is used in medical implants and food packaging. It has a glass transition temperature of 145°F and a high resistance to UV degradation, making it suitable for most shooting conditions. The inserts are printed slightly oversized and individually sized to fit using needle files. The STL files for the inserts can be found on American Gunsmith Reader Services 1.

the American Gunsmith website, AmericanGunsmith.info/lymanm77-download. The M77 sight mounts to a male dovetail attached to the barrel. To determine the correct height the distance from the centerline of the action to the center of the rear sight aperture with the rear sight set to the lowest position was determined.

The distance from the center of the M77 front sight to the top of the dovetail was subtracted from the rear sight measurement; the resulting dimension is the required distance of the sight base from the muzzle centerline. The sight base was also designed in On- Shape. The dovetail is a standard 60° with a 0.46" wide flat and the outer barrel diameter at the location for the sight is 9/16" diameter.

Once these features were modeled, it was a simple task to set the final base dimensions to place the top of dovetail at the proper place based on the previous measurements. The base was manufactured from an aluminum rectangular bar measuring 1/2 x 1". The base was milled to the required overall height and length before being cut from the bar.

To create the concave radius required to mate to the barrel, a 9/16" mill was aligned to edge of the base with a machine square and the mill table moved to position the cutter above the centerline of the base. The depth of cut determined the height from the barrel (0.250") and was easily checked with calipers during the machining process. The base was cut from the bar after the barrel radius was milled into the part to the required depth. A #6 mounting hole and counterbore was drilled into the base.

In preparation for milling the dovetail into the base, an adapter was made from a 9/16" brass rod. The adapter was milled to the width of the sight base and the two parts connected with a 6-48 screw. The adapter was clamped into the vise on the mill and positioned to take several light vertical "climbing" cuts with the dovetail cutter; top to bottom on the right and bottom to top on the left. The base was deburred, degreased, and treated with Aluminum Black metal finish.

It is important to thoroughly clean the part after machining as any residual oil will result in an inconsistent finish. Once degreased, the base was sanded with 400 grit paper, wiped down with isopropyl alcohol, and coated with Aluminum Black several times with light sanding between coats. Once complete, the part was washed in hot water and lightly oiled. The base was mounted to the barrel with a single 6-48 screw.

The radiused interface of the base to barrel provides stability, enabling a single screw for mounting. This configuration enables future "switch-barrel" options; anew base can be manufactured with this method and fitted to barrels of any diameter. Furthermore, customized front sight inserts can be designed and manufactured using CAD and 3D printing for any situation.

I made a travel box for the sights with some help from the 3D printer to keep the inserts organized and securely hold the front and rear sights. 3D printed parts for the rear sight cradle (after removal from the receiver base), a short dovetail for the front sight, and a tray for the inserts fit inside a small wooden box with a foam insert to hold the parts securely in place. These classic sights add a touch of class to a ground-up rifle project that started with an unbarreled smallreceiver Mauser action.

Fortunately, individual gunsmiths now have the tools to design with advanced computer models and create the custom hardware using both traditional machining techniques as well as additive manufacturing tools, including 3D printing. The availability of computerized modeling software and publicly-available 3D printers enables today’s gunsmith to go beyond their traditional machine shop fabrication capabilities to include specialized components as apart of their offering.

On Shape users can find the entire model, named "Lyman M77", in the On Shape public folder. Individual "part studios" are included for the inserts, base, housing, clamp screw, and eyepiece. There are dimensioned drawings of the insert and base as well as assembly drawings for the complete sight. AG