I found an obscure archived post on one of the Klashnikov sites from a few years back talking about how to make your own bolt hold open follower... basically after you expend the last round, it will hold the bolt open.
This appears to only work well on the steel mag followers because the polymer followers have a rounded surface on the "fake bullet" part of the follower. However, I wouldn't recommend using steel mag followers in your Bulgarian or Polish polymer mags as it can chew away the polymer and into the steel reinforcements.
If you pear into the mag well from the follower side (mag feed lips), look for dimples or raised edges on the mag body that clip against the follower floor. There are 2 dimples on standard steel mags that hold the follower down.
if you trim the hole on the one side by 1/8", and open up the other side by 1/8" (the one side does not have any hole to begin with) the follower will get closer to the feed lips.
This allows the bolt lug to hit the rear "fake bullet" part of the follower, and hold the bolt open.
Steel followers are like $1/ea at Tapco and maybe cheaper at gun shows.
Yes, that's the extent of what the follower can do when modified.
I've seen modified safety selectors that allow you to clip and lock the bolt open (basically there's a hole that is trimmed in the lever), but it's still not a true BHO ala AR15/M16s.
But I've been trying to figure out a way to use my brass catcher at the range where I can only load 1 round in a mag at a time, and this method is the only easy way to get the charging handle itself to not be covered by the brass catcher after each round is fired.
All of my Chinese mags do not have that special follower... they're raised but they're just like any other mag.
The BHO follower is useful because it lets you know you ran out of ammo, and because it prevents the charging handle from going too far forward when I have the EL brass catcher on. This way I can at least grab the handle w/o takng off the catcher, and change a mag.
My 30rd polymer mags do not have the BHO followers, and I'm not sure I'd want the bolt slamming into the plastic follower. The steel followers are hardened/treated.
That's what I have, Chinese 5 rd mags. Although the bolt can get close to hitting the rear of the follower on some of them (manufacturing tolerances) it never catches.
I'll have to keep an eye out for those followers... I don't think is useful to everyone, it just fit my application:
In MI, we're only allowed single loads at the firing ranges - that would mean taking off the catcher after each shot (and I can do about 200-300 rounds a day, single load only). If I could somehow keep that charging handle locked after each shot (not covered by the catcher) I could theoretically go through a day's load and not have to remove the catcher unless it was to empty it.
Now if I were allowed to use a full 30rd mag, I wouldn't really care about the catcher thing since I'd have to empty it out anyhow. THis is why I didn't bother modifying my 30rd mags.
There's a true BHO, i think it's http://www.geocities.com/akcatch