Are you referring to the bayonet adapter? Once you remove the screw and locking washer, it should slide out. There are no threads in the cocking tube. You might need to twist it back and forth a little to free it up, but it should not take much effort. Did Vector put Loctite on the screw?
If it is just the dust cover it should not have a screw; the dust cover should just have a detent pin that you press in to remove. Again it will require some twisting so that the detent pin does not pop back into place.
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