I usually do 300-ish to verify function, POI, etc.

I’m in the 500 round fmj and at least 100 SD ammo camp.

I’ll shoot a couple hundred target rounds and a few mags of HP ammo to be sure. My new Glock 21 I bought last year fired 230 grain ball ammo with no problems at all. I couldn’t get through a mag of HP ammo without problems. It hangs up on the 11th round in every mag no matter which magazine.

Verifying reliability is both a valid reason and an excellent "excuse".  Practice is good and shooting is fun.

Same here.

My carry guns have always been SIGs and Glocks (G17, G19, G22, G23, P226, P228, P229, P239, P220).  I have probably fired fifty thousand rounds or better (high quality government issue).  The only malfunctions I ever had were when we had to shoot special green ammo at the Fort Meade range, which resulted in whole days of malfunction clearing and training for every gun we had.  My life experience tells me that about the only way high quality guns malfunction, is from bad ammo, bad magazines, or bad luck.

I've never carried a SIG or Glock I haven't shot, but I wouldn't feel scared to do it.

I tend to lean towards the 200 +- ball then 50 carry. I will usually give it a light clean and lube first and again after I’m done.

With glocks, I'll put like 150rds of quality fmj in different weights (AE124 / AE115 / AE147) as I get used to the gun. Then I'll put like 5 mags of my carry ammo (124 HST) WITH one in the chamber through it. I'm doing this with 4 SHIELD mags now (but I'm also only loading it to 14+1 b/c 15rds just seems too greedy!). I was waiting for my new MAC Defense optic cut slide to arrive, so I'm vetting two of the mags tomorrow, and two next range trip.

I'm sure a LOT of people would say you need more than 5 mags of HD ammo, but I don't have the money for that.
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The worst part is when you have issues with a gun--if it chokes on the first 100, before you change something, then you want to put 200 rounds through it; I bought THREE Kahr CW380s, which SAY you need to shoot 200-500 (depending on who you ask) to break them in.  I kept trying to find one that would run, tweaking things, and then retrying it.  After about 1500 rounds, I finally learned my lesson with small Kahrs.  
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Also, the P365 had so many early issues and rolling changes, that I sold my first one and waited a little over year before getting another. Even then, there was a striker-tip change after about 1.5 years. Mine has never had an issue, and now it doesn't even have any primer drag.

About 1 magazine .

Why waste ammo?

500. You'll be really, really confident.  It's not just about the function check if it it's a new platform/model, it's also weapon familiarity exercise.  100-200 including a few of your carry rounds if you are just checking reliability after replacing or upgrading critical parts.

depends on gun

For my Kahr CM9 (been my favorite CCW)

small gun with super tight springs and stiff recoil spring

Clean off shipping / storing lubricant
Clean
Oil with my stock
Rack slide 200 times
Leave slide racked back for 48 hours

Gun at this point will be shot and not cleaned until after initial testing

Gun and 3 mags

4 types of ball ammo (1 preferred and 3 cheap inventory stuff)

all mags full capacity preferred fmj

all mags full capacity preferred JHP (if high capacity gun mark one mag and get at least a full load of your jhp through it and carry this mag in the gun)

all mags full capacity with cheap JHP with big mouth and sharp edges (sig ammo, silvertip, remington ultimate hd or hornady with that plastic tip) we all usually have boxes of various stuff we used in the past this has become test fodder

all mags with ghetto mix and match fmj, all mags with mix and match JHP

by 50 rounds of ball and 25 rounds of JHP you should be gaining confidence or seeing problems.

Once  a mag has passed the ghetto load with fmj and jhp mark the bottom and use the next mag. You don't want to drive home thinking you have a bad gun when you actually have a bad magazine

at 200 rounds I will carry the gun but this is a combination of rounds through gun and shooting to comfortable distances and shooting confidence at targets

at 500 rounds I will clean the gun

If  a gun survives the ghetto mags jhp and fmj alone it's most likely good to go

bigger duty size guns (50 rounds ball and 50 rounds jhp and your probably good) are more forgiving than small compact looking for a mechanical problem by design guns

This. I also shoot up all my loaded carry mags once a year, to use up the ammo and to make sure I'm still comfortable with them.

How is training waste?

Is your life going to depend on it working?