Does anyone purposely underload rounds to mix in and practice semiauto malfunctions? (e.g. failure to cycle/eject, failure to lock slide on final bullet etc.)?

I'm considering it.

Nope

I would never under load a round since it may stick a bullet in the barrel. I use dummy rounds for this. They are cheap to buy as dry fire rounds. You can mix them in a mag.

Yeah, loading a squib load is asking for problems. As larrys mentions a squib can leave a bullet in the barrel. Folks often feel something different but don't always register until after they pull the trigger and the next bullet runs into the stuck bullet. There is also the issue of explosive detonation with underloaded rounds although this is controversial.
Buy or load up some dummy rounds. Besides allowing you do conduct immediate action drills they also allow you to see if you flinch.
What is your remedial action for failure to cycle, stovepipe or fail to lock open? Its been a while but I thought they were the pretty much the same.

Tap, rack, assess has always worked for me. If it is a stovepipe, I tilt, rack and assess.

Buy the plastic colored dummy rounds then theres no chance of mistaking a real round for a dummy round.

We used to use RN cast bullets for practice. We would build a few dummies but paint the primer annulus with a black sharpie. Then we would mix in several dummies with the real reloads at the range. That way when you were loading your mag you didn't know if you got a dummy or two or not. When loading for carry or hunting we didn't use RN cast bullets. We also knew how many dummies we took to the range and made sure we left with the same number. The dummies were stored separately in a further effort to prevent them from being mixed up inadvertently.

I use the dummy rounds of a different color, OR load some fired CCI Blazer aluminum case rounds with a lead bullet and use epoxy for the primer pocket for the firing pin to hit.

quote:

Originally posted by larrys:
I use the dummy rounds of a different color, OR load some fired CCI Blazer aluminum case rounds with a lead bullet and use epoxy for the primer pocket for the firing pin to hit.

Dummies can be no primer no powder ya? With bullet seated you likely won't distinguish when loading your range quota.

When I trained under military instruction here in England we called them IA (Immediate Action) drills.

We always did them with totally drill rounds so could be done in a classroom instead of having to be on a range.

Range time being too valuable to waste on actually NOT shooting.

You would load a magazine and then fire a shot, as it were, and the instructor would call out something like:

"Gun stops firing"

You'd then do the first IA drill.

The instructor might repeat that or call out:

"Gun still fails to fire"

And you'd carry out the subsequent IA drill etc., etc.

So in effect we were told what had happened and had to respond to that.

This then taught you the automatic response to a, b, or c, etc., happening.

So that when it did happen it was ingrained in you that if gun stops firing occurred, or stoped firing and still wouldn't fire after the first IA you did it without thinking.

Personally I think that this is a better way than by simulating it with the odd drill round mixed in.

In fact, from memory, practice using live ammunition and drill ammunition AT THE SAME TIME was actually prohibited.

For the risk that the one became confused with the other.

We call it immediate action in the US army as well. But, never make up squib loads; good way to get a bullet stuck in the barrel, followed up by a full load, followed by a bulged barrel. Make up some DUMMY loads if you must practice this. Sorry, I see someone has already told you this.