TargetTalk

I have the 80 cubic foot scuba tank. When filled to 3000 psi , it may seem like a lot. Two hundred BAR ( 3000 psi) is what most of the air guns use. The refill level is about 100 Bar (1500 psi). Repeated cylinder re-fills from the tank drop the cylinder output quickly. I noticed that after a few dozen refills the manometer reads about 150 Bar, which now only leaves 50 bar until yet another refill is required.

I heard that if you have two tanks, in tandem, you can fill far more refills. The first tank, even if down to 150 bar, can partially fill your cylinder about 85%, the second tank requires only 15% more air from that tank to top your cylinder up to 200 bar. You can shoot far longer this way before refilling. Although my single tank is 75% full, my cylinder is about half full. It doesn't take much air to go from 150 bar to 200 bar.

How far from the dive shop do you live? Your proposal seems an awfully costly cure for what is at worst an inconvenience - refilling the tank. Most APs that I'm familiar with are good for 120 - 160 shots per charge X 20 - 30 charges before needing to refill the tank = doesn't look like a terrible thing.

If you really insist on having 2 tanks, consider keeping a full one as a backup. When the primary needs a refill swap them over. Then you only have 1 tank at a time that needs to go for a car ride.

With a cascade system (we used that at the club in my home town, the OTC uses it too), you still only take 1 tank for a ride at a time. You use Tank A to do the majority of filling and Tank B to give it that final push. When Tank A finally dies (can't get 50bar), you take it for a ride to be filled. Now you use Tank B for the primary fill and Tank A for the top-up.

It works really well and prolongs the trips to top up the tank. Even in a club setting with a dozen shooters (rifle and pistol) topping up, it took 6~8 months between fill-ups.

Another version:

Old divers like me often have a couplpe of 12 or 15 litre 200 BAR tanks lying around. They are just fine for diving, and for the basic AP fill. This means you only need to buy one 300 BAR tank for topping up.

BTW my MG1E shoots just fine down to about 80 BAR so I don't really need a full 200 BAR fill for a training session.

I think BrianM said it better than I did. Yes, it is an expensive alternative, but I was able to pick up my second tank cheap. The real issue is that you really need to refill your 80 cubic foot tank every time when it is only 15-20% depleted since the internal pressure drops dramatically. There is still a huge amount of air in it but at much reduced pressure. As Brian M said, one tank can do the majority of the cylinder filling , even when that tank is 50% empty, and your second tank "tops" up the air gun cylinder to 3000 psi using very little air. This second tank lasts forever. Two tanks together last alot longer than two separate tanks on their own.

My situation to get my tank filled requires that I take a 50 mile ( 100 mile round trip) to my "local" dive shop, drop off the tank and pick it up a few days later, ( another 100 mile trip) OR drive to my local firehouse and beg them to fill up my tank. I would rather donate some money to my local firehouse than the dive shop. But the problem with my firehouse is that they only meet on mondays, and even then , just some mondays, not all mondays. Two tanks would stretch this out ten fold.

I used to have a rapid fire air pistol ( LP-50) and I went through thousands of shots performing rapid fire practice. My air use was much greater than single shot use. Now my wife is into airguns , so the use has doubled.