Why are the MH bulb terminals on my Aquaspacelight frying themselves?

[RonSF]

I've had some peculiar failures in my Aquaspacelight recently that have left me puzzled.

About four months ago I lost a 250w Megachrome bulb that was only four or five months old. When I went to replace it, I noticed that the terminal at one end of the bulb was largely fried off. It looked like the metal had been cut with a cutting torch. Further inspection showed that most of the copper contact in the light itself was largely burned off as well.

The Megachrome bulb had a boxier end profile than the AB bulbs and it was difficult to insert when I installed it, so I attributed the problem to a poorly seated bulb. I've messed with HQI bulbs enough to know when they look to be fully seated and the ceramic end piece is recessed into the fixture's ceramic endcap. This bulb looked right when I installed it, but the burning result lead me to believe it must have been an installation problem on my part that caused the failure.

I ordered another end terminal from Aqua Medic and installed a new AB bulb this time. I made SURE that the bulb was fully seated. Now, four months later, the new bulb has done the exact same thing. Same bulb position, same end. When I pulled it out it was definately recessed all the way into the ceramic holder. Nothing had come loose (except for some small crispy bits of metal).

Is this a common HQI malady? Should I be cleaning the end terminals with alcohol like the glass envelope of the bulb. Fortunately, I have a Oceanlight not hanging yet that I was able to rob from for the time being. I noticed that the terminal is silver (spring steel?) instead of copper in the new light. Is this a design upgrade that might make this less likely to happen again?

[jdieck]

The only explanation is a false contact. I would replace the socket again and then insure that the center tab is pulled out enough, if not try forcing it a bit by pulling the tab a little as to unbend it. Screw in the bulb. A week after try to tighten the bulb a bit more as temeprature changes may affect the tighteness.

[RonSF]

Thanks for the suggestion, jdieck, but double ended HQI bulbs don't screw in. They are a bayonet style blade end contact and they should "click" in when seated. Both before and after the burning incident they looked fully seated. The HQI design isn't the most user friendly. It is a little unnerving having to press so hard on the bulb inserting it. Because of slight differences in the shape, the AB bulbs go in with less effort than the Megachromes.
I'm just surprised that the current in these things is strong enough to weld/cut metal. Electricity is in large measure black magic to me.