The guy obviously has no clue.
Therd are for sure hundreds of guys who have done hpa mods on various gjns.
Pressure of propane (i think i linked it befor) is over 100psi at 25° there are bunch of regulators that are adjustable between 5-200psi (perfect for airsoft and PB) the mag itself can handle the pressure up to 200psi no problem. The "weak link" will be the connection to the mag and so long as it is tapped properly it will be just as strong as the fill valve or the release vavle are as they are also brass fittings tapped into the mag and they hold propane with no issues.
Scroll down this page http://www.bingoairsoftworks.com/cat...pa-conversion/
And you will see a glock a kjw10/22 and a bolt action (either an l96 or a m700) mags converted to HPA look around the site and you can find out how to do it.
Just buy the parts you need and do it.
Only thing you may not want to do on yer own is drill and tap the mags.
Prety much any small machine shop would be happy to take your money to do that for you. Tho with a steady hand and a drill and a tap set you can do it on your own.
Its not rocket science it takes a bit of tinkering but it has been and can be done safely.
I think the PB guy just doesnt want you to have a cooler gun the him. Or he just doesnt know shit about regulators. What the hell kind of regulators do they use in paintball ( all the pros will have a regulator on their tank runningbout 200-250psi then a seccond regulator for 10-200 in line between the tank and the gun to fine tune the guy is just a moron dont ask pb guys about airsoft yes they sell airsoft guns but they know paintball not airsoft build your gun then go ajd rub it in his face like "hey remember you said it couldnt beb done? Shows how smart you are")
Hell just on saturday i seen Coach playing with a shotgun runnjng on either HPA or a remote line to CO2.
Its nothing new all the first airsoft guns wer either spring or HPA powered