Go to a hardware store and get an "easy out" for that stripped screw. They cost under $10.

Are you using a remote? If so, make sure you are not cutting off the ait with the plunger that depresses the pin of the tank. I had the same problem, and that is what it turned out to be.

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"Only the strong survive. The weak are killed and eaten as fingerfood." SDI SSgt Patterson, Platoon 1077 USMC

One option for removing the screw is if you have a dremel, you can cut a slot into what's left of the head so you can use a flat blade screwdriver to remove it.

Another option would be to try and see if there's a metric hex wrench that's a hair bigger. If it might fit enough to get a bite into it.

I keep some really cheap foreign ones around 'cause they are so poorly made that they seem to be a little larger or smaller than their intended sizes. That has worked out well in situations like that before. Since they are usually made out of cheap metal, they also mold to the fastener you're trying to remove Same thing for combination wrenches when trying to remove a bad bolt.

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Less in not More! I did the Math!

Could also be, (although not likely) that either the sear (situated in your grip/trigger assembly) or the part on the hammer where the sear catches, might be worn off enough that it wont catch the hammer.


[edit]
For reference, the sear is part number 02-35 as depicted here

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^Relic from the past