Boberg XR9-S Theory of Operation

Trigger, hammer and sear

The trigger group is a very simple system that works very well and very smoothly. The trigger pulls back on the trigger bar which in turn pushes the hammer group. They engage in different angles so eventually the trigger bar looses grip of the hammer bar and the hammer falls. Just before the hammer falls the firing-pin block gets moved out of the way by a protrusion on the hammer bar.

Locked breech, short-recoil operation with rotating barrel

After the firing pin hits the primer and sets off the round there's now the action-reaction thing going on. The key is to get the bullet out of the muzzle before the breech-end gets unlocked from the barrel. This is accomplished by a rotating barrel design. The first few milliseconds the slide and barrel move back as a unit. As the recoil block on the bottom of the barrel hits the takedown lever it forces the barrel to twist to unlock from the slide. This slows the recoil since it's spreading the impulse over a longer period of time. This, secondarily, saves space since the barrel doesn't have to tilt like a normal Browning-type design.

Extraction and ejection of spent case

Extraction works like a typical auto-pistol. The extractor is on the slide and pulls the case out if it needs help. The case is retained until the the back of the case hits the ejector and then it will pivot off the extractor and fly out the ejection port.

Round feed from magazine

While the slide is moving backward the bottom of the slide has a pair of tongs that will pull the case backwards out of the magazine. The round and tongs are guided backwards on the platform. The fresh round is feeding under the case that is being extracted.

Lifting ramp, camming ejector

The insert block has a nub that hits the flip link. This in-turn moves the platform on a parallelogram to lift up the fresh round in line with the barrel. This also helps with the ejection since it'll push the spent case out of the way. Just before the platform lifts the round all the way, the ejector gets cammed out of the way by a camming surface on the slide.

Tongs acquiring new round

The final part of the slide cycling after the platform has pushed the fresh round up in line with the barrel the flip-link performs a final action of camming the tongs back down ready to pick up the next round in the magazine.As the slide moves forward pushed by the recoil spring the tongs will lock on to the next round in the magazine and be held in place by the unlock block's ramps.

Trigger reset

As the trigger is moved forward, the tip of the bar falls off a ledge on the frame and slides over the sear link until it clicks past, ready to push it back again.[smugmug url="http://photos.vec.com/hack/feed.mg?Type=gallery&Data=21919761_pQvMKM&format=rss200" imagecount="100" start="1" num="100" thumbsize="Th" link="smugmug-lightbox" captions="false" sort="false" window="true" smugmug="true" size="L"]

- = -

This has been updated from the original post to correct some factual defects and brain farts. Much thanks to the folks at the Boberg Arms forum on this thread for advancing my knowledge of this weapon!

A special thanks to Arne, the designer of this gun (!!!!), for helping me out!  :-D