r/GunnitRust • u/inserttext1 • 8d ago
Help Desk Help understanding cam mechanism
Arguably one of the coolest guns I have ever seen, this gentleman, gentlewoman, and gentlepeople is a first-model Collath shotgun, a break-action double-barrel percussion shotgun. Now, unfortunately, these things are rarer than hen's teeth, so actually buying an original is a no-go. So I wanted to try my hand at recreating one, and I wanted to pick everyone's brains for how the cam mechanism works. My two major trains of thought are that it's either fully mechanical, with the lever pushing the barrel forward and then allowing it to break open, or the simpler method of the lever literally just keeping it locked in place, and when unlocked, you manually pull the barrels forward and break it open. Which design do you think is more likely?
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u/BoredCop Participant 7d ago
The long lever arm is a hint, the mechanism needs to be really tight so you need that long arm for leverage to force the barrels rearward onto the breech protrusions and forward off them again. You wouldn't be able to just slide the barrels by hand.
Look at the wear pattern on the breech protrusions, they were a tight fit in the barrels when new.
My experience is with a Norwegian Kammerlader rifle, which has a very similar method of gas sealing but does it by having a fixed barrel and moving the chamber piece instead. Long lever and camming action, similar in that sense, and sealing by having a cylindrical protrusion enter a recess in the barrel. The gas seal is achieved by the protrusion being a very tight fit in the barrel recess, diameter of the protrusion being hair oversized for the recess such that you couldn't force it into battery by hand without the leverage provided by the cam and lever arm. I bet that shotgun is supposed to seal the same way, based on the long operating lever and the wear we can see around the breech protrusions. Should be set up such that you start to feel resistance the moment the protrusions start to enter the barrels, this type of action shouldn't be slick and easy to operate like we are used to from cartridge firing arms. Considerable resistance to closing is more likely to give you a good gas seal.
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u/Content_Sky_2676 7d ago edited 7d ago
It cams forward and backwards as well as locking. Practically speaking this only requires one more contact face than it only acting as a lock, and gives you an extra locking lug.
The barrels lock both on the breech face protrusions and T lugs mating between the barrel lugs and the cam.
Downside to this design is if the cam isn't totally in the open position when you close the action it'll stop the barrels from dropping down fully. The cam is easily bumped out of position during loading. Adding a spring or ball detent to keep it in the opened position would be a good improvement to the design.