Thursday, October 06, 2005

Scuba tanks for airguns - part 1

by B.B. Pelletier

When you move into precharged pneumatic airguns (PCPs), a scuba tank may be a necessary accessory. You can get by fine with a hand pump, but most shooters will eventually want the convenience of a scuba tank, too. So I thought we would talk about them. Today is the first installment

Tanks come in different sizes and pressure ratings
The size of a scuba tank is measured by the cubic feet of air it holds. Because air can be compressed, the same physical size tank can hold different amounts (different numbers of cubic feet) of air. The construction of the tank determines how much air and pressure it can contain.

Most PCPs today have a 3,000-lb. per square inch (psi) fill level. If they state their fill in bar instead of psi, it will most often be 200 bar, which is 2,940 psi. Because of that, the minimum scuba tank you need is one that holds at least 3,000 psi. If you have a tank rated at a lower pressure, it cannot fill beyond its maximum pressure and will not fill a gun to 3,000 psi.

Size DOES matter - for scuba tanks!
There are small auxillary tanks that hold as little as three cubic feet. While they may be rated to 3,000 psi, they won't fill a gun very many times because they don't hold that much air. Yes, you can use them to fill guns. I have two tanks that are six cubic feet each that I use to top off my field target rifle in a match. That's about all they are good for. I would never consider them as my primary air source.


Six cubic foot tank on the left, 80 cubic foot on the right.
Both have a maximum 3,000 psi fill rating.


Here's the minimum scuba tank you can get away with
The minimum usable scuba tank for airguns rated to 3,000 psi is an 80 cubic foot, 3,000 psi tank. These are typically made of aluminum and weigh about 40 lbs. when full. They cost around $150 new, though you can sometimes find one on sale. How many times you can fill your gun from this tank depends on how large your gun's reservoir is and whether you fill to 3,000 psi. As a worst-case example, take the AirForce Talon rifle, whose air tank is a whopping 490cc. From this scuba tank, you'll probably get two full fills and another 13 to 15 partials. At the end, you may only be putting in a few hundred psi, so the number of shots you get will be fewer (but at the same power) than if you filled to 3,000.

Bear in mind that the Talon, with its big reservoir, will give you many more shots than other PCPs of similar power with smaller reservoirs. The amount of air needed to push a pellet to a given velocity turns out to be very close to the same, regardless of which gun shoots it. Only things like longer barrels can help conserve the air a bit.

A steel 120-cubic-foot tank is the same size as the aluminum 80!
You read that right! A 120-cubic-foot tank weighs a little more and gets pressurized to 3,500 psi, so you get five times as many fills. It costs about $400, though you can find sales on these, too.

The best tank is not a scuba tank
In recent years, airgunners have taken the carbon fiber tanks from emergency breathing packs and adapted them to charge airguns. Though physically smaller than the 80-cubic-foot tank, they hold a whopping 150 cubic feet of air and are pressurized to 4,500 psi. They contain up to 45 times as many refills as a standard PCP rifle, yet they weigh only half as much as the aluminum tank when filled. The down side is a cost of $600, plus it may be difficult to find a station to fill one. Most dive shops can't fill above 3,500. However, fire stations usually have a compressor that can fill these tanks, so there you go.

You don't have to be a diver to buy a scuba tank and to have it filled
There is no law that mandates a diving certificate to buy scuba tanks or air. BUT - and read this carefully - the diving industry is very tightly regulated by its operators. It is the dive shop that will or won't sell you tanks and air without a dive card, and there is no law that says they have to.

The diving community is well aware of airgunners' needs for high pressure air. Some owners choose not to sell to people without a dive card, but most will do it. I don't have a diving certificate but have rented dive tanks in a different state than my residence and had them refilled later by the same dive shop. It usually depends on how you approach the dive shop. The best approach is to walk in and introduce yourself. Mention that you are an airgunner, and 80 percent of the time the shop personnel will take it from there.

Your attitude means a lot
I know a man who was refused a fill from the same out-of-state dive shop I rented from, and he owned a business in the same town! But, this guy has a sandpaper personality that would make a preacher want to punch him out, so he may be the only guy they won't sell to.

There is a lot more to cover, so I'll do it in stages, with other articles in between, so we don't bore anyone.

6 Comments:

At October 06, 2005 8:07 AM, Blogger Joe in MD said...

If you can get 4500psi fills, the best deal by far in a tank is the Luxfer for $350 (but buy the net, boot, and valve cap while you are at it). This holds 106CF at 4350psi -- while not as much pressure as a 4500psi, most of them hold 88CF so you have a whole lot more air in this tank.

In Frederick, MD, the Brass Anchor is the best place for fills.

Best,

Joe

 
At October 15, 2005 4:31 PM, Blogger turtle said...

what is the hardware requiredt o attach the cabon tank you linked to w/ an airforce talon tank? It sure looks like a fine xmass gift

 
At October 15, 2005 4:56 PM, Anonymous B.B. Pelletier said...

Turtle,

Airhog.com makes the attachments, but I believe Pyramyd Air sells the cheaper tank. You'll have to find out.

B.B.

 
At October 13, 2007 11:30 AM, Blogger andreas said...

B.B.

I am trying to figure out why an 80CF tank can only fill two 490cc tanks completely...

Considering that they are both at the same pressure, shouldn't the 80CF tank be able to fill MANY more since
1.00000 Cubic Centimeters = 0.00004 Cubic Ft

??

Thanks a lot

 
At October 14, 2007 9:35 AM, Blogger B.B. Pelletier said...

andreas,

You have suggested Monday's post topic!

B.B.

 
At October 14, 2007 12:43 PM, Blogger andreas said...

B.B.,

That's great! Thanks for taking the time and effort to answer my question.

Thanks

Andreas

 

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