SCBA 30 Min 4500psi Carbon Fiber bottles

I have one out of date scba tank I fill it myself but the outside has no nicks or scratches in it I been filling it for 2 or 3 years now but I'm doing it under my own risk also paintball or diving place won't fill outdated tanks. There are some recertified tanks but I don't know what tests or how they consider what tanks can be recertified 
 
i got one on ebay for 65$ couple of years back .. no problems, i like it better than the 'new' tank i bought for 400 .. it was dirty and scratched up when i got it so polished it out with some meguires compound ... what you get with a used one is up in the air, what you dont want is a damaged one with a deep gouge in the surface or a bad valve so try to find a seller that takes returns and dont settle if its unacceptable, tell them you want a useable one .. anyway yeah, a 50$ fill adapter and firemans tank is grreat if you can fill yourself, with a yongheng etc ..

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I really just want one to pony off a 80cf aluminum SCUBA tank. Seems easier than taking the big one to the range, and it's extremely doubtful that I would want to shoot more than the number of fills I could get from the small tank at any one time anyway. 

Of course, if it exploded, denuded the range, cause me to loose an arm or killed the guys kid in the next stall... 
 
SCBA's have a VERY wide margin of safety built into them. "15 year life" is more like 30. The treatment they get in Fire Departments is way rougher than our intended use & treatment (imho). I was a firefighter, I speak from experience. Don't buy tanks unseen, if possible (get photos). If they show any scorch marks, cracked resin coating or obvious dents take a pass & keep searching. ALL my tanks are used but they look structurally sound on the outside & I've hydrotested them (I'm licensed for that). I have confidence in the wide margin of safety but I never forget that HP air has potential for great harm & act accordingly. I'm more cautious of fittings or hoses or compressor blowing out than my tanks.
 
I have two 30 min tanks that were given to me by a FF friend I think they are a little small I agree a 45min is a better way to go. Here on EBAY you get 2014 tanks for just $300 and still have almost have their life left https://www.ebay.com/itm/194751351579?epid=9002750464&hash=item2d5815cb1b:g:mY4AAOSwaJBh6KAl. Even after 15 years if you can get them to pass a hyrdo test which they probably will you will be fine. I then got the stickman to fill adapter here https://airtanksplus.com/product/stikman-scba-pcp-fill-system/ which works great. However by the time you do all that you basically at $600 and can get a a 45 min sized here for $600 ready to go https://utahairguns.com/airmarksman-4500psi-carbon-fiber-tank-6-8l-pre-order/  so the truth is SCBA's tanks are great if you can fill them yourself and get an old one cheap otherwise its a toss up between getting one that still has some life in it and the fill adapter versus getting one that is setup and ready to go brand new. The other option is to get a cheap gun compressor which I also have as well I save the bottles for when I go hunting and use the compressor when at home.
 
Mine are very clean, and were around $100 each. I have a cheap compressor, which is now a backup to a very not cheap compressor. I’ve seen some bottles in firehouses that I wouldn’t fill, and they think nothing of it. As Gerry52 said, there is a wide safety margin there, and with common sense and respect for what I’m doing, I believe I’m relatively safe. I think some of the fittings on the market are much more likely to cause problems. YMMV
 
I was contemplating the same question as the OP a few years ago. I decided if was going to spend $400 or so I would be better off buying a used SCBA and a Yong Heng rather that purchasing just a new tank for the same money. So that is exactly what I did, purchased a 30 min Scott tank (with 3 years left) from an AGN member that happened to live close by and a yong heng from ebay.

Tank=$100 YH=$250 CGA-347 adapter=$50 Total=$400
 
I was contemplating the same question as the OP a few years ago. I decided if was going to spend $400 or so I would be better off buying a used SCBA and a Yong Heng rather that purchasing just a new tank for the same money. So that is exactly what I did, purchased a 30 min Scott tank (with 3 years left) from an AGN member that happened to live close by and a yong heng from ebay.

Tank=$100 YH=$250 CGA-347 adapter=$50 Total=$400

How long to top it off from a session, on average? 
 
I have 11 out of Date SCBA tanks, all are filled with my 5000 psi SCUBA Compressor, we tend to use them up fairly quick when shooting the big bores, if you don't have a SCUBA compressor or a good PCP compressor rated to fill SCBA tanks, Buy one that has several years of life left and is recently Hydro tested, on the overseas Bottles, I'm not sure if Air filling Stations will fill them since they are not DOT Certified, you might get lucky and find a place to fill it, if you go that route, if I were you, I would look into a small portable PCP compressor, GX, Spirit tech, Yong Heng, and others can be purchased for under $500.00 on Fleabay, Amazoin and Wallyworld.