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RBL Shotgun Trigger Conversion: A double trigger shotgun can be converted into a single trigger even at a small shop. Here's how it's done.

RBL (Round Body Launch) is a line of shotguns designed and manufactured by the Connecticut Shotgun Manufacturing Company (CSMC, RBLshotgun.com, 860/225-6581). Created and guided by Antony Galazan, this company manufactures some high-end shotguns of classic design as well as their own in-house designs.

For this article, the gun of interest is a 28 gauge 2017 side-by-side boxlock with double-trigger mechanism. The customer came to my shop and declared that he cannot use this gun. The reason was simple--he has a small palm with short fingers. As a result, he could not reach the front trigger.

Extending the front trigger to the rear--which presents a challenge by itself--would not solve this problem as the rear trigger becomes unusable.

The evident solution would be a single trigger. I called CSMC but their technical staff explained to me that they do not have a conversion kit and would not take the gun in for single trigger conversion, despite the fact that they have a version of their RBL-28 with single trigger in their current production.

The customer needed a solution, and we decided that I would do it by myself. He also added the request to convert the automatic safety to manual and make a nonselective trigger. He wanted the gun to shoot the right barrel first and the left second. During this conversion I was trying to make the least amount of changes to the original receiver as possible. My fix was accomplished with the rear (left) trigger, sears, and a portion of safety block as the only mechanically-changed parts. Nothing was changed on the main body.

Decisions and Parts

The single trigger mechanism can either be mechanical, when the switch from one sear to another is a result of the trigger motion, or inertial, when this switch is caused by the motion of an inertia block in response to a counter-recoil of the gun. Either way, each single trigger mechanism has to incorporate the "third pull" blocker which often is the most challenging part of this mechanism. What exactly is a "third pull?" Simply put, this is another trigger pull immediately after the first shot. It is an unconscious pulling motion of the trigger finger. If this "third pull" is not blocked and the second sear is engaged with the trigger, the result is the gun doubling. I published a more detailed analysis of an inertial mechanism in the September 2000 issue as, "Understanding Inertial Devices On Single-Trigger Double Guns."

The advantage of an inertia block device for the single trigger action is that it can combine two functions: The switch from one sear to another and the disconnect of the trigger from both sears during the time of counter-recoil when the third pull happens. When the counter-recoil is over and the gun stops, the inertia block moves toward the sear under spring tension and engages the trigger with the second sear.

The inertia principle has become the most popular design in single-trigger shotguns and I decided to go with it for this conversion. I used a standard inertia block from SKB, just because I had it. In fact, any other inertia block could have been used or just made from scratch.

The single trigger itself for this conversion was made out of the original RBL rear (left) trigger by cutting and bending forward its arch. It also had to be heat treated. Trimming it to remove the unnecessary material, I left the post for restricting the motion of the inertia block. Another necessary preparation was shaping the sears for engaging with steps on the inertia block.

Having the inertia block itself, the next major question is how to place it in the action. Note the tiny space inside the action and a need of several more parts like a trigger return spring, link between triggers, inertia block, and safety. After some trials and errors I fabricated a link in the shape of a fork. This fork-shaped link is made from a high carbon steel flat 0.065" thick (1.65mm) which I heat treated to a spring hardness. The inertia block hinging hole is for inertia block hinging, and the fork hinging hole into the bolt extension is for hinging the fork in the bolt extension. The angle of the left side of the fork is for distributing forces of the spring, pushing the fork along with pushing the inertia block down. The bottom part of the inertia block with a step cut on the sear has a slot sliding over the lower hand of the fork for stabilization.

The trigger now is installed into the right slot of the floorplate. A screw serves for engaging the fork with the trigger. The assembled action without safety has a spring performing three functions: Forward trigger return, tight connection between link and trigger, and lowing the link into position for engagement with each sear. This multi-functional spring saved space and simplified the action.

Trigger Sequence

The sequence of events before, during, and after each shot is thus. First, when the barrels are opened by turning the top lever, the bolt extension moves to the rear with the inertia block and the lower hand of the fork sliding over the screw. The hammers are cocked, raising both sears up to the level of the inertia block steps.

Second, when the barrels close the bolt extension with inertia block moves forward and the right sear engages with the step on the right side. The left sear on the level of the other step remains unengaged. Pulling the trigger will trip the right hammer and the shot goes off. During the recoil of the first shot none of the parts change their position.

Third, during the counter-recoil when the gun moves forward, the inertia block tries keeping its position, swinging to the rear and releasing the right sear, moving it down. The trigger post restricts the swing of the inertia block and ensures that the sliding bottom part of it will stay on the lower hand of the fork. Keeping at rear for the duration of the counter-recoil, the inertia block prevents the engagement with the left sear and the "third pull" does not cause the double shot.

Fourth, when the gun stops after counter-recoil the inertia block moves forward and the other step engages the left sear. Then, the next trigger pull will trip the left hammer and the second shot goes off.

With all this accomplished, the manual safety should be fabricated and installed. Among many ways of doing that the easiest one is to use the internal part of the original safety. The original safety block is modified by brazing a small U-shaped part on it and allows for the original safety to work.

Conclusion

The result of this conversion moved the trigger position back 10mm to a convenient place for my customer. In addition to this, his two other requirements of having a manual safety and a non-selective trigger were implemented. Since this conversion the gun went through numerous shoots and hunts, proving itself reliable.

An inertia single trigger is not a new design and the conversion could have been done in many different ways. My goal, though, was to make it as simple as possible and avoid structural changes to the main body of the receiver. In fact, only the original sears, rear trigger, and the safety bar were slightly modified. The major principle part of this conversion is the fork link, which may be fabricated for any other conversion of this type.

by Sergey Lyalko
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Title Annotation:WORKBENCH
Author:Lyalko, Sergey
Publication:American Gunsmith
Date:Jul 1, 2019
Words:1258
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