I think Suck Lead may have inadvertently answered your question in this recent thread.
Put 9 rds in with no problem,but #10 was real tight.
Tried to insert mag,but would not seat and latch,had to remove 1 rnd to get mag to seat and latch.
This is my 1st glock and the only other autos i have had since 1968 have been colts or clones.
Are these mags defective or when they say 10 rnds, do the mean 9 in mag 1 in chamber.
Your mags are not defective. It takes them a while to break in actually. Just keep using them with 9 rounds, and try every now and then to fit #10 in there. It will happen eventually.
BTW, I have five G30 factory magazine bases if anyone needs them. Few bucks, enough to cover shipping. I can't use them.
This is from the Midway site. Pretty much the same thing that's been said.
-Jeff-Glock magazines have very stiff springs when new and may be extremely difficult to load to full capacity. It may be necessary to use a Glock magazine loader (generally included in the Glock case with the handgun) to load the magazine to capacity or near capacity.
If the last round appears impossible to load, for example if the magazine should hold 15 rounds and it will only accept 14, then leave it loaded with 14 rounds for several days to allow the spring's tension to decrease. After a short time, the magazine should then accept its full capacity, but it may still be necessary to use the magazine loader. After several cycles of full capacity through empty, the magazine will be easier to load.
Thanks for the replies guys,I am not used to pistols that require a breakin period to perform as they are advertised from mfg.
Any of my old colts held the stated amount of rounds right out of the box and the pistols and mags were never a problem till something wore out/broke after a few thousand cycles