In my experience, the 10 rd G19 and G17 mags do not run with the same reliability as the standard capacity mags.
To check this, I once loaded 100 rds into 10 of the CA compliant 10 rd mags and another 100 rds into 6 standard capacity G17 mags at Todd Green AFHF class–not one of the 10 rd mags ran reliably, while all of the standard capacity mags ran perfectly.
I live in one of those ban states and use a lot of glock 10 round mags for gssf shoots and other matches limited to 10 rounds or less to save wear on my precious pre bans. Never an issue with ball hollow points or lead reloads
Even if they worked as well (and they don’t), I could never understand why someone would run a gun designed to hold 15 rounds crippled to 10. I would go with a smaller, more size efficient, or same size larger caliber. I don’t follow the logic, especially since the same reliabilty is not there.
I have a 3rd gen G23 with an x300 on it.
I have about a dozen (13) round mags that have the current follower in them with Wolff +10% springs and they work fine.
I have some (10) round mags that I wanted to use for the range and I have nothing but problems with the x300 mounted. Take off the x300 and they seem to run fine for the short amount I have used them.
I have two 10 round Glock 23 magazines that have always worked as well as my 13 round mags. I have never had any trouble with them.
Anyone have a theory for why some people have no issues at all with 10 rounders, and others have all sorts of trouble with them?
All of my stuff is a few years (or more) old. Is it the new stuff that is having issues?
That is a very good question. My 10 round magazines were purchased during the 1994-2004 ban.
I ordered some 10-rounders for my G17 and my G19… Just to have in case they may be needed in some particular circumstances. They arrived today… I’ll test and report back.
I will also say that the 10 rounders do not last very long. After a few hundreds rounds they become suspect. Downloading one prolongs the service life, but not for long. I have actually been able to send them into Glock CS before as the mags were ejecting live rounds (volcanoing) during admin loading with the slide locked back, prior to racking into battery.
All in all, for defense use, if choosing between a pistol designed for 10-rnd mag and a high-cap model using a neutered mag, I think I’ll just stick with the pistol designed for 10 rounds. 
Good lad.
When I got my g19 used it came from a ban state and I got two 10rd mags with it. Have not had a failure yet after about 100 rounds through each. I use them only for practice though since I live in a nice state
None of the 10 rounders I’ve ran has been problem free.
They belong in the trash / bargain bin…
or commie states
I have a Gen 3 G17 & live Behind Enemy Lines & used 10rd mags exclusively & have had 0 problems in “Thousands” of Rd’s,easily over 5K++ !!! I guess some guys & guns are different,but I have always loaded to the MAX 99% of the time,never had a problem with Lock Back,FTF,FTE,etc,Hmmmm,guess I am lucky !!! I have a couple Pre-Ban mags,but just got them in the last few months,they worked fine for the short time I used them,but are in the safe for “Safe” keeping !!! 
I have noticed the “Notch” on a few of them (10Rd Ones) shows some wear,but they still have held up & run fine !! I have 10 mags,& ALL get used and rotated equally !!! Just sayin,
YMMV
Thanks, all, for the comments. Sure sounds like Jeckyll & Hyde… I guess it’s a total crap shoot as to whether these mags run reliably or not. I still haven’t tried out the 10-rounders I just bought for my G17 and G19, but will do so at some point, for sure.
During the last ban, I had bought two Glock 19’s. These were LE guns. At the time the 15 rd magazines had followers marked “3”.
I acquired about 9-10 of the 10 rd magazines. These had different followers that looked like the top of the follower was cut in half, for a lack of a better term. All of the 10 rd magazines would have the same issue. If you load the mag with one round, then try to load a round into the chamber, the tip of that round would hit the bottom of the feed ramp of the barrel, preventing the round from going up the few ramp and chambering. Happened on any 9mm Glock I tried.
I played around a bit and discovered the followers from the 15 rd mags would fit into the 10 rd magazine bodies. The combination of the followers from the 15 rd mag and the body of the 10 rd magazine proved to be reliable for me. Glock CS shipped me enough followers to convert my stock of 10 rd magazines.
Wether this will work with the current generation of followers, I can’t comment, as I do not live in a region with a magazine capacity limit.
For now…
This is exactly what I do nearly every day for dry fire practice with a single snap cap. I do it on my 19, 17 and 26s. I also do it on my other Glocks too. I have never had one single issue with it. Always loads properly, and goes click.
I have never looked at my followers all that closely. Never had a reason too, since they all work perfectly. I will go have a look next time I crack the safe open and see if I can match my followers to either of the descriptions you gave. This difference in followers COULD be the reason why some have no issues and others do. Thanks for posting.
Interesting mix of results posted here. I have 6 10-round mags for my 19, and 4 10-rounders for my 34. The 17/34 mags are much more difficult to load as compared to the 19 mags.
I have about 2500 rounds through the 19 with zero malfunctions, all with the 10 rounders. The 34 has close to 2k through it with no issues other than the normal brass to the face that seems to have been cured by the new ejector.
It sounds like it may be an age issue. The majority of my my mags are Gen 4, and all are 2010 or newer.
For you guys running them without any drama- is anyone running them with a rail mounted light?
To date, I have not.
What is your theory here? I am guessing the basic design of the magazine body, base plate, and follower are all the same as standard caps, with the difference being single vs. double stacked and a different spring? (I may be wrong here, asking a question)
Is your theory based more on the thought that the light reduces reliability with all Glocks, and the 10 round mags only make the problem worse? Basically, one potential weakness, plus another potential weakness adding up to more of a problem?