I must be doing something wrong

A few months ago I purchased a 12 gm. cylinder adapter for my Hammerli 850. I put in two cartridges, screwed on the brass cap fully (which I assumed punctured the cartridge tips), screwed the adapter into the air chamber port, pulled the trigger, and -- nothing happened. With the help of a friend we disassembled the adapter, releasing the pressure, and found that only one cartridge had been pierced. I put in another cartridge with a penny between the two, put it back into the gun, pulled the trigger and -- nothing. I finally threw the thing away -- it was after the return period.

I recently read a review of the adapter; it received four and five stars from everyone. The only (justifiable) complaint was the price. Convinced I had purchased a defective one I bought another. Again, I put in two cartridges, screwed the adapter into the gun, pulled the trigger and -- it worked! However after perhaps twenty shots the power decreased. Opening up the adapter I found that only one cylinder had been pierced. I added another cylinder, putting a penny between them, screwed it into the gun, pulled the trigger and -- nothing! Again!! 8^(

Two other notes: 1) the first time I screwed the new adapter into the gun it was difficult. Once the threads had engaged slightly it was very difficult to screw it in all the way. 2) depressing the tip fully against a wood post did nothing; no pressured was released.

I'm at my wits end!! Does anyone know how the adapter is supposed to operate? I don't want to be out another $99. Thanks for your help.