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jellyroll · New Member

hi
anyone have the dims for cutting back the main tube on a qb78 to fit a 12ci reg bottle.
better still diagrams/pics/tech drawings???
Do you have to do any mods to the piercing pin??
Would like to hear from someone who has done this mod .
tx

rsterne · Moderator

If you are planning on mounting the bottle directly, as in a QB79.... be aware that the mounting system for the tank block is designed for CO2 pressures.... There has been at least one catastrophic failure caused by the regulator bypassing and pressurizing the main tube to 2600 psi.... This resulted in the tank block/regulator/bottle assembly separating violently from the gun when the mounting screws sheared.... Shocked

If you want more information, I suggest you read my bottom post on this page regarding safety with HPA conversions:

http://airgunhome.com/agforum/viewtopic.php?t=3165&start=30

In regards how much to shorten the QB78 tube, I would imagine that as long as you miss the valve you would be fine.... and I would remove the piercing pin from the valve to get better flow.... You might be safer if you use a QB bulk-fill adapter simply screwed into the existing end of your QB78 tube and then a remote tank and regulator assembly.... Whatever you do, make sure the gun is projected by a 1.8K burst disk.... Wink

Bob

jellyroll · New Member

thanks bob
planning on staying well within the CO2 pressure range. I am not planning on mv much above 700fps. Co2 is really costly here so hence the mod. This is a starling rifle. Small birdies at close range, must be silent.
tx
jellyroll

kanyon · Silver Status Member

rsterne · Moderator

My comments about a regulator failure still apply.... make SURE the downstream side of the regulator (and hence the gun) is protected by a 1.8 K burst disc....

Bob

jellyroll · New Member

Yup I'm a saffa. Laws here are not too bad as far as airstuff goes. Airguns of .22cal and above and where they excede 6ft/lbs need a licence.
Below that ie .177 and .20 dont need a licence.
Silencers are allowed and modifcations where the caliber is not changed. There really is NO way for anybody to enforce these rules here though as the cops are stretched to the max with real crime. Unless you get caught doing something silly which would be unlucky or your own fault.
As for the boks well I think they suffer from schitzo sports delusions.
will make sure the reg is set as you say. Had a bad incedent with some paint spray guns we made for a TV ad. Made charged bottles out of super thick wall pvc pipe attached to modified garden spray guns dressed up to look like rayguns??!!??. Charged the tubes and one of them poped an end cap turning the workshop and every thng in it blue. Very conservative when it comes to HPA now!