Bullpup and Electric Trigger, Part 1

Bullpup rifles typically have less than great triggers; along and spongy travel with a pull weight of more than seven pounds. This is the result of the additional parts and friction in the linkage from the forward mounted trigger back to the fire control group. I admit to being a trigger snob and have installed aftermarket triggers on several rifles and handguns. A shorter, lighter trigger pull improves accuracy by reducing the amount of effort and time to fire the shot while holding the sights on target.

This is particularly noticeable when shooting offhand. After reading a few articles about poor trigger pulls on bullpup rifles and pistols such as the Remington XP-100 and the Savage Striker, I wondered if there may be a better It would have been nice to use the smaller one. way to actuate the trigger. Instead of using a mechanical linkage that has to get past the action and magazine to the fire control group, I decided to use an electric solenoid to actuate it.

I didn’t have a bullpup to try this on, so I decided to build one based on a Ruger 10/22. I measured the pull on my 10/22 and it was 3.5 pounds with 0.26 inches of travel, which is not bad. I had installed a trigger spring kit years ago; it reduced the force required but not the length of travel and didn’t have a crisp break. I tried the aftermarket Ruger fire control group; it didn’t seem any better than what I had. I found some suitable 12 volt solenoids on Amazon and ordered one that I thought might work.

It had a listed pull force of 20 Newtons (N) which is 4.5 pounds and a travel of 10 mm (0.39"). The solenoid was small and light; roughly 1.5" long, 1" wide, and 1" high and weighed only 2.5 ounces. I built a simple fixture to mount the 10/22 action and solenoid to see if it could pull the trigger. I connected the solenoid armature rod to the regular Ruger trigger with a simple loop of 1/16" diameter steel wire.

I did not want to further modify the Ruger fire control group because if this project turned out to be a bust, I would reassemble the rifle in the stock configuration. The solenoid didn’t have enough pull, so I bought a more powerful one. It was rated at 55 N (12.4 pounds) and 10mm travel. It was considerably larger and heavier; 3.5" L, 1.5" W, and 1.25" H, and weighed 12.0 ounces. It actuated the trigger with no hesitation.

Out of curiosity, I measured the force that the solenoids exerted with my trigger pull gauge. It turns out that the solenoids exert their rated force after they’re energized and the armature is fully retracted into the coil, not when the coil is initially energized. The amount of force is proportional to travel of the armature; the more the armature is retracted, the greater the force that’s exerted. The small solenoid only had a few ounces of pull when first energized but it took 4.2

I used connectors on the wiring for easier assembly and disassembly. Armature return spring is located on the right side of the solenoid. It requires very little force and travel to close the contacts. pounds to pull the armature out of the coil when it was energized. The larger solenoid only had two pounds of pull initially but over 10 lb. after being energized. Apparently, it retracted the armature sharply enough to overcome the Ruger trigger spring force.

I realize all of this may have a "science project" vibe to it. Bear with me. The next question was how to power the solenoid when installed The safety lever has a small tab on the top which prevents the lever from pivoting out of the grip. in the bullpup? I went to the local battery store and bought the smallest 12 volt lead acid battery they had; one typically used in kids’ scooters. It measured 3.75" L, 1.0" W, and 2.5" Hand weighed 12.9 oz.

I looked at cordless tool batteries but couldn’t find any that were smaller than the one I had selected. The next step was to design an aluminum chassis to mount the barreled action along with the butt stock, pistol grip, and fore end. After a few hours on the drawing board, I came up with a reasonable design. I decided to locate the battery in the buttstock above the solenoid since that was the most volume available.

I wanted the ability to use the 25round magazine which had a pronounced radius that wanted to interfere with the pistol grip. I moved the pistol grip forward to clear the mag when installing or removing it while trying to keep the length of pull between 14- 15". I reduced the angle and length of the pistol grip to help accomplish this. The pistol grip contained the micro-switch that acted as the trigger and a second micro-switch for the grip safety.

The microswitches area momentary, "normally open" design and require 7 oz. of force and 0.10" of travel to close the contacts. This results in a very light "trigger" pull. Closing the switches energizes the solenoid which retracts the armature rod and operates the Ruger trigger in the normal manner. When the trigger switch is released, the armature spring returns the rod to its initial position and the trigger resets in the normal manner.

Since the Ruger trigger retains its normal operation internally, there isn’t a concern about it firing if dropped. The solenoid return spring requires 1.5 lb. to compress it and prevents the armature from pulling the trigger if the rifle is dropped. I thought the addition of a grip safety made sense with such a light trigger pull. In hindsight, the normal Ruger cross bolt safety is adequate and rifles don’t typically have or need grip safeties.

Before investing the time and effort to fabricate with metal, I built a wooden mockup to determine if I had a feasible concept and how the overall design functioned and handled. It was assembled from thin sections of solid and laminated wood with screws and epoxy. It was light and rigid but not particularly durable. The left side and the top and bottom sections were The trigger blade has a hole at the top originally intended for a spring that would hold the blade against the switch. The spring was not needed.

Left, top, and bottom frame sections are shown. The receiver action screw is on the far right, forward of the mag well. the chassis. The components were attached to these pieces and simple, flat covers installed on the right side to enclose everything. The safety, mag release and bolt hold-open lever were accessible as on a normal 10/22. The mockup was rather "boxy" and crude (no one will ever mistake me for a cabinet maker) but proved the electric trigger system worked.

The length of the battery increased the stock length and the length of pull ended up at 15" which was okay. I was concerned that the weight of the solenoid and battery (24.9 oz. total) in the rear of the stock would make the rifle overly butt heavy. There’s plenty of clearance to insert and remove the mag. The cross bolt safety, mag release, and bolt holdopen lever are accessible in the normal manner.

The weight was rear-biased; the mockup balanced between the pistol grip and the mag well (without a scope) but felt comfortable when shouldered. The 20" barrel helped compared to a 16.5" or 18" barrel. Without the scope, the mockup weighed 6.44 lb. Installing the 3- 9×40 scope and riser added another 1.75 lb. to the front of the rifle which helped offset the weight in the butt stock. The overall length ended up at 29.5" compared to the original 10/22 at 38.5".

The original 10/22 weighed 5.25 lb. without the scope, the barreled action weighed 3.25 lb. and the stock 2.00 lb. These weights include an empty 10-round mag. Solenoid Details Before I started on this project, I did a little research to see if there was any history on this type of trigger actuation. Solenoids are used in many industrial and automotive applications, but I didn’t find anything on firearms.

Reducing the lock time (the amount of time it takes for the lock or action to fire around when the trigger is pressed) typically improves accuracy. Flintlock rifles obviously have very long lock times whereas modern rifles have times measured in milliseconds. That’s about all I know about it so I’ll stop there. Using a solenoid to actuate the trigger does not have an effect on lock time.

It does "slap" the trigger but since it and the barreled action are rigidly mounted to the chassis, it shouldn’t affect the accuracy. Testing would determine whether that was true. Remington introduced the Model 700 Etron X rifle in 2001 to reduce the lock time. They replaced the regular firing pin with a fixed and

Top: Right side view with 3-9×40 scope installed on the riser. Yes, I know, it looks like a wooden box with a rifle in it. insulated firing pin that contacted the electrically-fired primer when the bolt was closed on a chambered cartridge. When the trigger was pressed, an electric current was sent through the firing pin to the primer. This reduced the lock time by eliminating the motion of the firing pin. It required a special primer, but the rest of the cartridge was the standard design.

It used a 9V battery, trigger and safety switches and a computer to manage the electronics. The rifles were very accurate. The drawback was that you had to buy the ammo from Remington and could not reload the cases as Remington didn’t sell the primers. I couldn’t find any information on how many Etron X’s were sold or when it went out of production; I was unaware of the Etron X until writing this article.

I recently saw that Midway USA had these primers listed for $0.44 each, but of course, like all the other primers, they were out of stock. On my 10/22 original stock, the fore end is inletted to free float the barrel except for the last 1.5", closest to the muzzle. The 10/22 only has one action screw so pulling the barrel against the fore end is necessary. Some models have a barrel band that secures the barrel to the fore end.

The rear of the receiver is supported by narrow rails on either side of the stock, the fire control group fits between these rails. The more recent Ruger competition model 10/22 rifles have a second action screw to secure the action to the stock and completely free float the barrel which is an improvement over the standard model. I decided to support the barrel on the chassis at the same place as the 10/22. The support was 1.5" long and I bedded the barrel in the support.

I also bedded the rear of the receiver on rails that I glued to the inside of the chassis. This provided a rigid support for the action. I assembled all the components and dry fired it many times with snap caps. I added a cheek rest to make the stock more ergonomic. At the Range I tested the 10/22 action in the original stock after mounting the scope to the receiver. I shot from the bench and offhand at 50 yards.

I then installed the action in the bullpup chassis, installed the scope, and repeated the accuracy tests. Mounting the scope on the bullpup required installing the scope rail on top of the forend of the chassis as opposed to directly mounting it on the receiver and required the riser to get the scope to the proper height. I was concerned about how precisely I had aligned the barreled action and the scope rail with the chassis.

When I zeroed the scope, I was pleasantly surprised to find that it was aligned almost perfectly horizontally and just needed a small amount of vertical adjustment. The electric trigger system worked well and was completely reliable. The trigger pull was light and crisp as expected. Adding the scope moved the center of gravity forward causing the bullpup to be balanced at the pistol grip which was more comfortable. I used a 10-round magazine with standard velocity 22 LR ammo, not match grade, for these tests.

I shot three, five-shot groups and averaged them. The accuracy of the bullpup was slightly better than the standard 10/22. From the bench, the 10/22 averaged 1.76" while the bullpup averaged 1.70". Shooting offhand, the 10/22 averaged 4.73" and the bullpup averaged 4.07". Not a big improvement, but the 10/22 trigger was already pretty good with the 3.5 lb. pull. I’m sure there would be a larger improvement when compared to a typical bullpup trigger.

The next step will be building the aluminum chassis which I will cover in Part 2. I will change the pistol grip; the mockup grip wasn’t as comfortable as it should be. The new chassis will be slightly narrower than the current one at 1.88" wide. I’ll aim for 1.5" and make the rifle more aesthetic. AG