How the vintage Diana ball-sear trigger works

[MDriskill]

Wrote this up earlier for another forum. For what it's worth...!

The parts diagram below is a Diana model 25D.

1. The inner trigger sleeve (part no. 17) is fixed into position within the receiver, by the two stout cross pins in the action (19 and 20). The famous ball bearings (18) sit in holes in this sleeve. These holes are sized to permit the balls to move inward and outward a small amount. The spring guide (15) sits on the front of this sleeve.

2. The outer trigger sleeve (16) moves backward when the gun is cocked, and flies forward a short distance when the gun is fired. The firing spring (21) is trapped between the two sleeves.

3. Note the outer sleeve has three recesses arranged around its center. These have two functions: a) pushing the ball bearings inward when the sleeve moves backward; b) halting the sleeve's forward motion against the rear of the spring guide after firing.

4. The outer sleeve also has a cut-out underneath, that engages the two spurs on top of the sear (23/2). This is what you "feel" when pulling the trigger (the ball bearings have nothing to do with it).

When you cock the gun: a) the piston contacts the outer sleeve and pushes it rearward; b) the firing spring starts to compress; c) the outer sleeve recesses start to push the ball bearings inward; d) the annular groove around the piston stem moves toward the ball bearings. When the sear catches, all this is locked into place - the ball bearings in their innermost position, restraining the piston. When you pull the trigger, the firing spring pops the outer sleeve forward, and this all reverses itself in a hurry.

Hints for working on this trigger: a) use a spring compressor, and put a rag around the back of the receiver as things come out, to keep ball bearings and little springs from flying around the room; b) to start disassembly, pull off the sheet metal rear cap and put a little compression on the inner sleeve - the retaining pins should pretty much fall out; c) to start re-assembly, "glue" the ball bearings to the inner sleeve with grease, stack the sleeves on the spring guide, and then drop this mess in front of the spring compressor; d) insert the firing spring after the sleeves are partially inserted past the rear of the receiver, which will help restrain it; e) use a punch or other dummy pin to align the cross pin holes (it will take some patient wiggling around but the pins do go back in!).

[Mole2017]

I've wondered if anybody tried anything like that. I guess it costs extra to implement in a rifle, but how did they work out for users? Any difference in trigger effort/feel? How about durability?

[MDriskill]

I may be misunderstanding your comments, but the ball-sear trigger was not some experimental thing. It was used in all of Diana's top sporting rifles for more than 30 years - the famous models 25D, 27, and 35 barrel-cockers, and model 50 underlever.

It's pretty much the definition of reliable - hundreds of thousands of these guns were manufactured. The trigger's moving parts are heavy steel stampings, three ball bearings, and stout small springs.

The ball-sear trigger is adjustable, and when correctly set up gives a superbly smooth two-stage pull with a crisp release.

[Mole2017]

A little misunderstanding, but no problem. I was pretty sure a German rifle company would be doing this for a good reason, but just didn't know. So a really nice system. Pretty neat.

Can a ball sear handle more than conventional sears, e.g. an experimental gun design with higher loads on whatever sear system a person would try to apply to it? I can see it certainly holds reliably, else all our quick disconnect lines wouldn't use something like it.

[MDriskill]

An interesting question. I don't know why this type of mechanism couldn't handle the tension of any mainspring usable in a spring-piston power plant.

An ingenious feature of the design was the fact it requires no hand-fitting; it's all made of ball bearings, springs, and formed stampings. Economical, durable, and perfectly suited to mass production. But admittedly a pain in some ways, the worst being that removing the spring and piston requires dismantling the trigger into its individual little bits.

The so-called "T 01" trigger used on later Diana designs addressed this issue - it's basically a ball-sear mechanism enclosed in an easily-removed module.

[DanD]

Thanks for the explanation, Mike.

Even after rebuilding my 35 a few times I didn't fully understand how the sleeves and bearings work, but you clarified it.

Thank you!
-
Dan

[MDriskill]

Thanks Dan! It's truly an original and ingenious design, I think.

An interesting wrinkle on the models 35 and 50, is that the bigger receiver tube gives the bits more room to move around. So the firing spring needs a tiny little spring guide of its own!