Laser Trainer for Dryfire Practice

This is a laser trainer using 3D printed components with electronics self contained in a barrel mounted configuration. My goal was to create a laser trainer that could adapt to a variety of long rifles that would not require readjustment of the firearm's sights. That is, the laser would be adjustable to match the sight's point of impact. This configuration has been tested with telescopic sights up to approximately 20 meters. I have also included an untested "iron sight barrel bracket" file  that will lower the laser and hinge support components below the sight line by 20 mm to accommodate iron sights to facilitate biathlon training.  

The unit detects the release of the firearm's firing pin with a piezo sensor mounted in the electronics housing. The electronics then fire a 50 mSec laser diode pulse compatible with ITarget detection app ( https://www.itargetpro.com/ ) or most other photosensitive or IR detectable targets (https://www.instructables.com/Dry-Fire-Laser-Target) as an example.  The laser diode is available from most electronic distributers or can be salvaged from a laser pet toy (Dollar Store) for a few dollars.

The drawback of using the piezo sensor is that the laser is triggered by the vibrations made when re-cocking the bolt. This necessitates moving the barrel off target so these unintentional pulses are not registered.  This should not be an issue for casual practice.

I am including two circuits that may be used- one based on Arduino Nano, and another using discrete components based on a 555 timer. The Nano version is likely easier to build for novice makers as only a few other components are required to be sourced. The link to the Dry Fire Laser target above provides info on programming and using the Arduino Nano. For more detail on using the Nano also check out this Instructable : https://www.instructables.com/Arduino-Nano .

For this Laser Trainer (Arduino Nano Version) you will have to use the program code (LaserDryFirePulse.ino) included in the "files" section above . For the code to work you will have to make all the connections as detailed in the included schematic. 

The discrete component (555) version may appeal more to a hobbyist who already has a collection of components. The piezo sensor, also marketed as a guitar pickup, can be salvaged from an old smoke detector, or as with virtually all the required components, ordered from Ali Express or Amazon. Note that all the resistors used are 1/4 watt.  The capacitors used should be rated at 20V or higher.  It may be more cost effective to order an assortment of resistors or capacitors than try to purchase individual items.  Attempt to salvage components from old electronic devices where possible. Any NPN type transistor will work.  As far as the resistors and capacitors, try to keep with 20% of the target values, especially R2 and C1 which dictate the pulse width of the laser. 

Notes on assembly:

1) I have built both versions of this trainer (Nano and 555 Discrete Components). The discrete component schematic shows connectors that should be ignored- just solder the wires directly to the circuit board. In this case I used perforated prototyping board which seemed to work fine.  

2) The use of printed bolts on the square laser adjuster (hinge support) is preferred to keep the weight down on the front end of the rifle. The holes themselves should be tapped at 1/4-20 threads. Running the printed bolts through a steel nut, and printed nuts over a steel bolt is advisable to clean up the threads.  Printed bolts and nuts design courtesy of  AgentSCAD https://www.thingiverse.com/thing:4394046

Also the threads on the "barrel bracket" connecting the top straps should be tapped at 6-32.  Alternatively the holes could be drilled out to clear the #6 screws and use #6-32 nuts to secure the straps.

3) The mount was designed for a 20 mm diameter barrel. To accommodate smaller barrels, The "barrel adapter" file is included. This particular adapter was designed to adapt a 14.5 mm diameter barrel to the mount. Intermediate size barrels may be accommodated by using just one half of the adapter set, or designing a new adapter with two cylinder halves - outside diameter of 20mm and inside of diameter matching that of the barrel. Going larger than 20 mm will likely require a redesign of the "barrel bracket" part.

If the barrel has front sights, the top straps may require notching or redesign.  Or alternatively, nylon tie straps may be used to secure the mount.

4) If using with a rimfire rifle, in order to protect the firing pin, it is recommended to use snap caps or TPU printed dummy round such as https://www.thingiverse.com/thing:3536377

5) All printed parts use PLA, at a 0.2mm layer height and 40% infill, with the exception of the nuts and bolts which require 0.1 mm layers at 100% infill.

6) The "Center and Housing" part may require a slight reaming with a 1/4 inch drill bit to accommodate the laser. 

7) The laser itself must be focused with the lens mounted on the forward end. This is done by rotating the brass bezel containing the lens.  The laser should extend just out of the "Center and Housing" part allowing the adjustment. I recommend leaving this to a final step, using the "test" switch to turn on the laser continuously then rotating the bezel to find the smallest elliptical dot on a surface at about 5 meters.  Once this is done, "lock" the bezel with a drop or two of hot melt glue to prevent the laser from losing focus. The focus of the laser has a dramatic effect its range.

7) Please review attached photos for further details.

Using the laser Trainer:

Mount the unit to the end of the barrel, control box down. Back off the plastic centering adjustment screws so the laser housing is roughly centered.  Proceed with laser adjustment as described in (7) above. Put a mark on the surface at about 5 meters and look through your scope at the mark.  In most cases at this short distance you will need to turn down the scope power and adjust the parallax if available for the most clear picture. Loosen the steel hinge bolt and bring the laser pinpoint close to the right elevation in the scope view then tighten the steel bolt as a coarse adjustment. Move the plastic adjustment screws until the laser pinpoint  aligns with the center of the scope crosshairs then tighten the lock nuts on the screws.  At distances closer than this setting the laser dot will be lower, and further will be higher.  Adjust the plastic screws accordingly.  Do not adjust the scope crosshairs themselves as you want to keep you sights true for "real bullets".  Note that this plastic mount is not a precision device and will need to be adjusted prior to any use.  It should stay fairly true for a session, but will have to be adjusted for any change in distance (plus or minus 1 meter).