Those are tapered screws and the head has broken off, you can not tap it through from the top. It is going to be tricky getting that apart. I would think long and hard on that one before proceeding. You might try an easy out, a skilled welder might be able to tack on enough material to back it out, last resort would be drilling it. Not a fun job.
Imagine what damage might have happened if David wasn't observant enough to recognize that the advice given in the post QUOTED above was totally wrong. All three solutions given to remove this pin or screw were wrong. Not even close.
I didn't offer any advice because I simply didn't know how this gun was assembled. I suppose I could have taken a guess, but it would have been irresponsible to make a wild-assed guess sound so definitive. This is just another example that you should not believe much of what is posted by wannabe experts on the internet. Thank goodness gunmaker came along with the correct and straightforward solution.
I learned this in a big way several years ago when I began researching the use of feed grade molasses as a rust remover. I found quite a few posts that incorrectly explained the chemistry behind it, the effectiveness , and potential damage that some "internet experts" warned could happen.
When I finally bought a 50 Lb. sack of dried molasses and mixed some with water, I proceeded carefully by using some old rusty items that didn't have great value. It worked great, and it quickly became apparent that much of the bad advice given came from guys who never even tried it. I guess some people just have a pathetic need to pretend that they know way more than they do.