Newbe air tank owner with questions

You've probably got a 3/8" hose. Yes there is a lot of wasted air with a hose that size. If you search for a "microbore" hose you'll notice a smaller and more flexible line. The microbore hose holds the same amount of air over 12" that the 3/8" hose holds over 1", very big difference! I like the braided microbore hose that AoA sells. It's more expensive and uses BSPP fittings but, it's super flexible!
The scuba shop filled you too fast. It's a common thing and that's why they gave you a time to come back on your first visit. They should have either told you to come back later or offered you a discount for a partial fill.
You are CERTAINLY in your right to request your bottle be filled to 4500. Your paying to have to bottle filled, not "somewhat-partially-close enough" filled. You also are well within your right to be a little ticked off. But, don't push it too far. They could refuse to fill you again and then you'd be searching. 
Many of us have switched over to home compressors so that we don't have to deal with the headaches of having someone else fill our bottles. But, to do that right can be a significant expense. 
Tom

lamarkeiko, Tominco is 100% right. My dive shop will do the same thing if allowed (fill to 4500 and say they're done). If you have them fill the tank, then wait 15 or 20 minutes, then top off again to 4500 psi, you usually can get it close to the full pressure. My dive shop in San Diego fill the tanks while in a tub of water to try and keep them as cool as possible. Plus, when just getting your tank topped off from say 3200 to 4500 psi, they don't get nearly as warm as a full fill from zero psi. I normally take more than one tank for my fills, usually I have 3 with me. Luckily, its only $5 per fill.

I think you probably have the below SCBA fill rig from Airtanksforsale if you are using the CGA347 connection "firefighter's tank" . If not, you are using the DIN300 fill rig. They are similar except for the connection to the tank. I think they do come with a 2mm microbore hose, but the issue is the void inside the valve block holding a significant amount of air. You can get a shorter microbore hose, like the one below, but it probably won't help significantly. The SCBA rig from eBay also comes with the microbore hose and its the one I use. But like I said, that one and the Airtanksforsale one have a void in the valve block that hold a portion of air and vents more than you would expect. No way around it. If I read this wrong and you are using the standard Great White or Tiger Shark then disregard this post...

Airtanksforsale SCBA fill rig:
http://experthpa.com/cart/cart.php?m=product_detail&p=66
Airtanksforsale DIN300 fill rig:
http://experthpa.com/cart/cart.php?m=product_detail&p=69
eBay SCBA fill rig:
http://r.ebay.com/8vTD0k
eBay 2 ft. DN2 microbore hose:
http://r.ebay.com/5kMUNG

Lamarekeiko, when you open the bleed valve do it fast so that the check valve in your gun will close faster. If you do it slow then the hose stays closer to being equalized longer allowing a tad more air to bleed down from the guns tank/cylinder. Another thing I do is add a small 1/8" pipe threaded valve, high pressure of course, just upstream of your bleed valve. With this valve in line you'll only bleed off the hose and bleeder and not all the fittings and gauge all the back to the tank.
Just a thought....
Jimmy

Lamar, kind of a cluttered photo but you can see the valve I use furthest downstream. I actually use this valve to do the filling instead of the cylinders valve. Nuvair.com has some small valves.
Jimmy

If that's the only gauge on your set up I would put one on after that last valve so you can see and regulate what's going into the Airgun and it's a good way to make sure the gauge on the gun is right....Right now I take it you are just watching the gauge on your Airgun when you fill being it looks like that big gauge is only giving you your main tank pressure reading between valves...I would take and move the black handled valve next to your main valve and then put a gauge by your pressure release knob, you can use a dead head in the hose end to check tank pressure if you need to see how much pressure is left in your tank.....it keeps the valves close to the tank so there is less chance of bumping and breaking off that long pipe set up......JMO.....



edit for valve...

Is that an N2 setup?

Centercut, it's just breathing air (Grade D), 4500# cylinder. I have two of these, One in the garage and one in the shop in my backyard. They last a loooooong time..

Imold, I misspoke earlier. Most of the time I use the cylinder valve to fill the gun and I do watch the gauge while filling. When the gun is full I close both valves and just bleed off the hose up to the last black handled valve. This leaves the gauge pressured up for several days if I don't use it but eventually the pressure leaks down a little. I've tested this gauge against my Crystal digital test gauge and it's almost right on. I can also just leave the end valve shut, crack the cylinder valve to check the cylinder pressure.
Jimmy

very informative thread information greatly appreciated !!

Do all or most scuba shops fill to 4500? Local shops claim they can only fill to 3000, or just over. If scuba shops won't/can't, where else? Forget the fire dept, they won't even talk to you round here. 

The scuba shops within 100 miles of me only fill to 3200, same as the VFD's around here so I went ahead and bought a AV Compressor and don't worry about it anymore. Can't see driving 4 hours round trip for a day or less at the range depending on what I'm shooting and sure I could buy a couple more tanks but that would be the same cost or close to buying a compressor so Compressor it is.