I think that was an ill attempted trigger job. I know that if you grind the top of the sear on an angle, you get an quicker release.
There is one on MCB without battery for around $175. Not mine btw.
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Not sure how people feel about them but I was checking out CL and www.truckeesurplus.com had 3000 and 4500 regs for 17 each. Bulk prices too.