I have an old Armalite M15-A2 I took to the range today. I was having some issues with my bolt hold open keeping my bolt open. When I was shooting the bolt would hold open on the last round, even when I removed the empty magazine. When I placed it on the table the bold catcher would release and the bolt would slam home. I am thinking the bolt hold open is worn out, how easy is it to change out the bolt hold open?

Thanks.

It is supposed to continue holding open even after the empty magazine is removed. Even after a new magazine is inserted. Until you press the bolt release, pull the charging handle or bump the stock enough that the bolt backs up off the hold open a tiny bit. If you lay the rifle on the table on its left side, there's a very good chance its own weight will press the hold open release.

I might not have been clear. Yes the bolt does stay open like it should on the last round. However on occasion the bolt would slam shut without the lever pushed.

It could be a magizene issue not enough spring pressure engaging the bolt catch, or it could be the bolt catch is simply worn out.

That can happen when you jar the rifle or lay it down on its side roughly.

Friction between the bolt face and the hold-open, under pressure from the action spring is what keeps the bolt back. Anything which makes the bolt move backward even a tiny bit, releases the friction between the bolt face and the hold-open, and the bolt hold-open spring promptly snaps it back down out of the way, allowing the bolt to slam home.

If there were something wrong with the bolt hold-open, it would be randomly popping up and stopping the bolt while you were firing, instead of only when an empty magazine or your finger activates it.

Changing out the bolt hold-open parts isn't very hard, or expensive, but again, what you are seeing is normal bolt hold-open behavior. It's not like a half-cock which requires deliberate interaction to release, it's just a bit of friction, and jarring the rifle can cause it to release when that bolt carrier group moves.

More than likely you're setting the rifle down too hard, or onto the left side and the table is hitting it.

The BHO is supposed to do its job until it's pressed, or the charging handle is operated to chamber a new round from the fresh mag.

Sounds like your rifle is functioning properly...

I often send the bolt home (administratively, like putting it away) by slapping the butt. I've never seen an ar15 type rifle that didn't do this (and I worked in an armory for a year).

The hold open appears to have a gash in it. I believe that is the problem. Time for a new bolt catch.