XR9-S recoil spring?

"skeptics thought that fitting a recoil spring into this gun was impossible, there was actually a space for it, but in an unconventional location - along the lower-left corner of the barrel, allowing the spring working length to be virtually the full length of the gun"

I'm not sure I understand where the recoil spring is...a diagram would help, thanks.

Also, are there any other differences in the mechanism of the XR9-S versus XR9-F?

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Permalink Reply by Arne Boberg on September 4, 2010 at 12:02am

I don't know of any precedents to an off-center recoil spring in firearms. However, off center force-producing devices are used everywhere - in household appliances, cars to high-speed assembly and process equipment. Often, it is not practical to put a spring, air actuator, electric actuator or hydraulic cylinder exactly aligned with the center of mass of an object. The key to successfully applying off-center loading is GUIDING, which depends on the aspect ratio of the guides. I have seen some terrible aspect ratios (guiding length divided by guiding width) in the machine design field - 1:1 or less and the mechanisms still work (all though they have limited life). A good practice is to have to have at least a 2:1 aspect ratio for long life (I always used at least 3:1 when designing machines). The XR9-S has a 4.3:1 aspect ratio side-to-side and a 31:1 aspect ratio up and down. When you think about it, guns that have the spring on center will swing the slide to the left some of the time, and to the right some of the time, when taking up the play. The XR9-S in theory biases to one side, which should produce better grouping. I have seen no issues related to wear in the side-to-side direction.

elsullo said:

Think of the M1 Carbine: the location of the single recoil spring does not matter since the frame guides the slide and torque is minimal..............................elsullo

urbock said:
Arne,

This isn't intended as a criticism, just curiosity. What firearms engineering presidents, if any, are there for the asymmetrical recoil spring?

Arne Boberg said:
Here is another view showing where the slide spring is located: http://www.bobergarms.com/photo/underside-of-slide-assembly

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Permalink Reply by elsullo on September 16, 2010 at 12:24pm

I thought of a successful pistol design with an off-center recoil spring: the Intratec Tec-22. These are mostly junk, but some of them work well somehow---the design has no ejector to aid the extractor! The bolt is fully guided by the frame, and so the off-center recoil spring works perfectly and torque is not an issue.................................elsullo

Arne Boberg said:

I don't know of any precedents to an off-center recoil spring in firearms. However, off center force-producing devices are used everywhere - in household appliances, cars to high-speed assembly and process equipment. Often, it is not practical to put a spring, air actuator, electric actuator or hydraulic cylinder exactly aligned with the center of mass of an object. The key to successfully applying off-center loading is GUIDING, which depends on the aspect ratio of the guides. I have seen some terrible aspect ratios (guiding length divided by guiding width) in the machine design field - 1:1 or less and the mechanisms still work (all though they have limited life). A good practice is to have to have at least a 2:1 aspect ratio for long life (I always used at least 3:1 when designing machines). The XR9-S has a 4.3:1 aspect ratio side-to-side and a 31:1 aspect ratio up and down. When you think about it, guns that have the spring on center will swing the slide to the left some of the time, and to the right some of the time, when taking up the play. The XR9-S in theory biases to one side, which should produce better grouping. I have seen no issues related to wear in the side-to-side direction.

elsullo said:
Think of the M1 Carbine: the location of the single recoil spring does not matter since the frame guides the slide and torque is minimal..............................elsullo

urbock said:
Arne,

This isn't intended as a criticism, just curiosity. What firearms engineering presidents, if any, are there for the asymmetrical recoil spring?

Arne Boberg said:
Here is another view showing where the slide spring is located: http://www.bobergarms.com/photo/underside-of-slide-assembly

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Permalink Reply by Arne Boberg on September 17, 2010 at 1:07pm

Thanks for those examples, guys!

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Permalink Reply by Jose A. Montalvo on September 19, 2011 at 7:22pm

Hey, Mr Boberg designed this on a computer. I'm sure he has all bases covered, and wouldnt be surprised if this gun could be fired in zero gravity with total reliability. In fact, it works without the recoil spring if fired pointing straight down.

He has indeed built a better mousetrap and the proverbial gun world will beat a path to his door. I'll put in my order once his production capacity exceeds the need for a waiting list. Yes, I am too impatient. Waking up at 3:00 AM Christmas morning, is considered "sleeping in" at my household.