74 cu/ft tank ??

Got the news that my back ordered tank will be shipped next week.
called the dive shop to learn that they won’t fill a tank to 4500 psi even if it’s rated for it. (No expectation why/we just don’t do it). 
Being new to the PCP world I’m curious about how many rifle refills 4500 psi would give me compared to the lower PSI they fill for divers. (3000 ?? Not sure)
I’m shooting an HW-100 Carbine (unsure of the tank volume)
 
If I were in that situation, I would give serious consideration to cancelling the order for the 74 cu/ft tank and buying something like a Hill Pump to directly fill the gun. Mine fills a FX Wildcat from 140 BAR to 230 BAR in 90 seconds and will fill up to 300 BAR if you have a gun that needs that much air costa about $1200, built like a tank ... just saying.
 
A couple of options for you. Check with your local fire departments and find out which firehouse fills their tanks. If you are nice, they may help you out. :~) 2nd option, buy a decent HP hand pump. I used one to fill my HW 100 for over a year before I went the tank and compressor route. I believe your HW has a 175cc cylinder, it will be printed on the label as to its volume. You may have the smaller one though, which has 105cc capacity. If you have the 74 Cubic ft tank, that gets filled to 4500psi, then fill your HW to 2900 psi and shoot it down to 1200 psi before you refill it, you would get a bunch of fills out of the 4500 tank. Check AOA's website under tank fills. Plug in your numbers in the calculator and get your number of fills. Keep in mind that you don't need to fill to the HW capacity of 2900. Also, an 80 CF scuba tank filled to 3000 psi will not yield as many complete fills. Don't be discouraged. Pumping is not that bad, just go slow. Once you get the pump inline pressure filled, it will probably take about 75 - 100 strokes to get to your 2900 fill level. 
 
I have the following:

1. Two HW100's. One with the stock/steel 175cc cylinder and another with a Ratworks titanium 235cc cylinder.
2. 74CF carbon fiber tank
3. A dive shop that only fills my tank to 4350psi

I always refill after three full mags (42 shots) and realistically get around 20-25 rifle fills despite what the calculators say.

Hope this helps!
 
It is only THAT dive shop that does that. My local dive shop will fill to 4,500 PSI no problem. They do recommend leaving the tank overnight though to allow it to cool and then they can fill a few times due to heat. The do offer the option to fill quickly while I wait, but then when I get to home or the next day, the fill is only 3,900 PSI or so. Shop around for a better dive shop. 

Also, being a dive master myself, they do fill cylinders to above 3,000 but only if they are rated. 
 
Update
Called the place and the guy says that 3000 is the maximum psi they will fill too.
The upside is that it’s closer than the dive shop. 
Still haven’t checked out the Fire Dept.

I would recommend taking the tank in to the FD to check on filling along with a good description of certification and use of the tank. A call is possibly more easily dismissed with a NO. There was quite a bit of interest in the HP airgun concept on the part of the people in the FD when I initially took my tank in to see about getting it filled (many years ago now) and thereafter they filled it with no concerns until I got my first compressor.
 
When you can get compressors for less than $400 now on amazon you are much much better off with one of those than a tank. I have both 2 used 44 cu tanks ( I got for free) and a compressor. Tanks are great if you hunt and want to fill in the field (which I do) but otherwise compressors are the way to go. I am luck my paintball shop will fill to 4,500 psi but not all do.
Compressor2.1628405169.jpg

 
Good to know. 
My first inclination was to get a compressor, obviously for convenience.
What I found is that they can cost into the thousands. I also read of many gunners unhappy with them breaking down. I figured if the higher end models were unpredictable then the cheaper ones would be a waist of money.
So it seemed like a tank was the more dependable choice with less aggravation.
I’d like to hear more about the unit you have. How long have you had it??
$400 sure seems like a great price as long as it doesn’t go to compressor heaven in a week. 
 
A 6.8 or larger carbon fiber tank is a valuable asset and dependable source of air. Twelve volt compressors in the sub $600 price range are like Russian roulette. Some last for years, a disproportionate number of them do not. When a 12 volt compressor breaks down, most of the time it's terminal. Then you have a $300-600 boat anchor. If you are mechanically inclined then at least the Yong Heng class of compressors have most repair parts available online. If you want to direct fill without a tank, a Hill EC-3000 is probably the safest bet in a direct fill compressor. However, it is somewhat overpriced at $1200.

Truly reliable compressors do start at about $2500. Unless you are truly dedicated to the sport and own multiple PCP's, a compressor in this category is not a priority. Compressor reliability is an inverse relationship to price. A dependable source of high pressure air is hard to come by. A co-operative fire department, paintball or dive shop that gives 4500 psi fills for $10 and is within reasonable driving distance is a valuable asset for anyone to have until they're ready to invest in a high quality set up. A friend with a compressor is even better.