DEFECTIVE HDP .50 PISTOLS

I purchased an UMAREX HDP .50 GUN from Security Hyperstore in Gateway. These pistols are pretty much useless since the gas cartridges leak gas after a few shots resulting in the pistol being totally useless. I have established that the seal/Orings are defective in these pistols and have to be replaced before the pistols can be used again. This costs time and money since they accept no responsibility for this manufacturers defect. It also appears that there have been other customers who have experienced the same problem. Guys don't ever consider buying these pistols as they will inevitably fail when you least expect it. I have had 3 failures since the purchase of the pistol which I have hadly ever used.