What is so great about a C300 or 350? What is the difference between them.
Well, you'll have to buy my logic to end up agreeing with me, but it goes like this:
For my absolute failsafe reg, I'll take a downstream valve as a backup. Why? In case of a stray grain of floaty coral sand getting stuck between the poppet and the balance chamber causing a malfunction in a balanced second. Yeah, unlikely. But I'll bet you've maybe had a balanced 2nd get stuck after you got tumbled in a rough beach entry once in your career. So you know what I'm talking about. Bang a downstream valve on your thigh, and youre likely good to go again. Maybe not with an S-wing poppet and balanced 2nd. So anyway, that's why I'm even looking at it. European cavers have jumped on the C300 series over similar logic.
The C300/350 has a big G250 exhalation valve. They have a barrel with huge flow due to the cutout, and a venturi adjust sleeve kindof like the A700. The flow characteristics of the case are fantastic. Smaller than the G260, and I think even a little smaller than the S620t, but with that special barrel. Anyway, the air delivery is second only to the new S620t and A700. Part of that is due to the poppet. Unlike the S-wing, where air passes through the wings of the poppet and swirls around the spring before going out the barrel, the C350 has an end design with no obstruction to air flow. The spring is on the other side! But here's the thing: I think it says something about friction and counterforces that Scubapro can use the S600 balanced 2nd poppet spring (supposedly lighter) in a downsteram design! Unless I'm "misremembering" that's exactly what they've been able to do in the C300 (see below re: C350).
The lever looks wonky, like the old (awful) X650, but the pivot points in the barrel have been redesigned for really low friction. It opens very wide and the bent-rod lever has half the friction of the S600 or A700 levers on the diaphragm disc.
Add it all together, and it's a go-to reg for guaranteed performance.
Now all that said, it's still unbalanced, so it's very critical to tune to your balanced first's IP. I wouldn't be this enthusiastic if using an unbalanced first stage too.
But with a relatively constant IP, you can absolutely count on this reg's performance. Tuning it for very light cracking might be problematic, since it would drift out of tune and might freeflow after the LP seat takes a set from the orifice. After all, Scubapro doesn't use silicone seats with a seat-saver orifice spring like Atomic. But with average cracking efforts (1.4"), it is the definition of dependable,.
The C350 had only one substantive change: the poppet spring, which I think used to be the same as the S600 spring, has now been coated. The tolerances in that new barrel are a little finer, and the old spring had reports of binding. There were cosmetic changes, too, but only to distinguish it from the previous model.
It's hard to get parts here, because few use it in the US. I think the problem might have been horror as soon as technicians saw the X650-style lever, and made some erroneous assumptions. Or maybe the fact that it was paired with Subgear firsts and was seen as second-class kept it from breaking out. Or maybe nobody much gravitates toward unbalanced seconds except us technophiles. But it's EASY to service and breathes the best of any downstream 2nd I've ever serviced. I'm still waiting for parts from Europe to upgrade two recent eBay C300 finds to the C350 model. Grab 'em if you can find 'em!
I'm slowly making them the alternate second stage on every reg set I dive - Scubapro or Apeks or Atomic or XStream. Hopefully I'll find a used one for all of them.
