1. Who made the malfunctioning magazines? Taurus? Triple K? Some other maker?
2. If the new magazines are pushed past the release and all the way in, when you press the release again do they fall out of their own weight? Or do you have to pull them out?
3. When the new magazines are pushed all the way in, and you fire the pistol, do they feed cartridges correctly? Or do they cause occasional jams?

Finally, is it possible that there are two different models or iterations of your PT738 pistol, and the new magazines are for the other iteration?

I had one of these TCP's, and although the gun worked "most" of the time, I had a hell of a time getting it to cycle three different types of JHP's. The Hornady load did the best, but even then I would get at least one stovepipe out of a magazine. I never had a magazine that did not seat though. Sounds like Steve knows what he is talking about with the different magazines.

Originally Posted by Steve M1911A1

1. Who made the malfunctioning magazines? Taurus? Triple K? Some other maker?
2. If the new magazines are pushed past the release and all the way in, when you press the release again do they fall out of their own weight? Or do you have to pull them out?
3. When the new magazines are pushed all the way in, and you fire the pistol, do they feed cartridges correctly? Or do they cause occasional jams?

Finally, is it possible that there are two different models or iterations of your PT738 pistol, and the new magazines are for the other iteration?

Thanks for the response. The new are Taurus mag's. They will fall out when the release is pushed. I have not fired the weapon with the new mag's. They arrived and I tried them both empty and filled and they will not slide in.

The problem, then, is most probably a sharp edge at the top of each of the two new magazines. The edge catches against the ramped bottom of the magazine release.
The other, less likely, possibility is that the new magazines are just a tiny little bit bigger than the older ones, at least in width.

Compare new magazines to old. Look for sharp or protruding edges, where the new ones might hit the magazine release. Look for a small difference in width, too, using a caliper.

If the problem is a sharp edge, use sandpaper to round it slightly, and try it again. To fix a protruding edge, you may need a small file. Polish off the sandpaper scratches and file marks.
If the new magazines are too thick, you will probably do best complaining to Taurus USA about them, rather than fixing them. However, the best fix might be changing the angle on the bottom of the magazine-release tab.

We need to be aware there are 2 different mags for the TCP 738:

TCP 738 Magazine for Guns with SN 6000 and higher

TCP 738 Magazine for Guns with SN below 6000

I believe you bought the incorrect mags for your TCP.

Originally Posted by Steve M1911A1

...Finally, is it possible that there are two different models or iterations of your PT738 pistol, and the new magazines are for the other iteration?

Originally Posted by Leo

We need to be aware there are 2 different mags for the TCP 738:
TCP 738 Magazine for Guns with SN 6000 and higher
TCP 738 Magazine for Guns with SN below 6000
I believe you bought the incorrect mags for your TCP.

Aha!
Thanks, Leo!

Originally Posted by Steve M1911A1

Finally, is it possible that there are two different models or iterations of your PT738 pistol, and the new magazines are for the other iteration?

Sorry, Steve, I didn't see your comment in the post #2 . Just like you said, Taurus made the new mag for the new 738 after a lot of complaints on jamming on the older 738.

i just tried two different brand new ProMag clips in my TCP 380, and they pop out of the gun. I can give the clip a tug and it will pop out of the gun!!

Originally Posted by marconewt

i just tried two different brand new ProMag clips in my TCP 380, and they pop out of the gun. I can give the clip a tug and it will pop out of the gun!!

Maybe you should try using magazines, instead...

Some "third-party-made" replacement magazines are made to slightly incorrect dimensional specifications. Occasionally, for instance, Triple-K has been guilty of this flaw.
Could this be the case with your magazines?
Maybe the top edge of the hole into which the magazine-release's retaining stud fits is placed too low, keeping the retaining stud from fully seating into the magazine's cut.