Need help with bulk CO2 fill problem

[Fisherdude]

I was going to bulk fill my QB78 this afternoon and when I hooked up the hose to the rifle, it wouldn't seal.  It has been sealing fine.  There must be an o-ring or something in the quick disconnect that has gotten lost?  Can someone tell me what size o-ring I need to get?

[Frank]

You might be able to use a small hook and get the old ring out. There are metric and sae sizes of o-rings. If the ring is missing try getting the ring out of another connector to find the size....

[Rodents Rapture]

Never had any luck rebuilding those things. Usually dry-rot or a nick in the o-ring. I have them for sale if you want to buy a new one. Pre-fall price is $10.00 include shipping in US.

[CharlieDaTuna]

Yes, there is an o-ring in the female side of the qd connector. It sets low inside near the bottom. A little tricky to get out. Just use a needle to get it turned on end and pick it out. There is no real rebuilding of the connector itself other than replacing the o-ring.

It isn't uncommon for them to get damaged and you should keep a couple of spares on hand. Just a little silicone on the male side of the connector helps to prevent the damage.
I don't remember the size but you can get the o-rings almost anywhere that sells paintball stuff and might even be able to get them at Wal-Marts. Seems like I've seen them there in the paint ball section but I could be wrong.

You can also pop the old one out and take it a an Ace Hardware and match one up but it will probably only be a 50 or 60 Durometer and not last too long.

 If/once you know the size you can order a hundred of them from McMaster & Carr for a few dollars and would last you a lifetime. If ordering them, I would order them in 70 Durometer as they will not damage as easily and still not be too hard coupling up.

[Bentong]

If you don't have a slide check to vent co2 before disconnect, the o-ring tends to get blown out. This is what I replace mine with #010 O-ring from > http://www.theoringstore.com/servlet/the-2358/010-E70-EPDM-O-dsh-ring/Detail
way cheaper than Mcmasters. Found that out when I ordered urethane o-ring for my QB's and they didn't last long, swelled up till it leaked. The EPDM o-rings sealing good with no swelling.         

[Rodents Rapture]

 You may also have a micro-nick on the fill nipple in which case you'll be replacing o-ring, after o-ring, after o-ring