I am sure it is common knowledge on here, but I just made a discovery. The 5900 mags will fit in the 4003 TSW but will not fit in my 4006. The 6906 mags will also fit in the 4003 TSW. The 4006 mags seem to function perfect in the 4003 TSW even though they are a tad loose when compared to the 5900 mags.

This is weird to me. Anyone know why this is the case?

Thanks,

Rosewood

Maybe not "common knowledge". but it is widely known that the double stack 9mm and 40s&w mags have the same front-to-back and side-to-side dimensions.

40s&w mags have a bump on the lower front face of the mag to prevent them from being fully inserted in to a 9mm mag well.

59xx mags will insert in to any 40xx (double stack) magwell without regard to TSW or base model configuration.

This concerns me as it creates the very real possibility of the dreaded "9, 9, 40 KABOOM!!" although I never seem to hear of it happening.

Yup! But the 69xx mags are too short to reach the 4003TSW slide.

Base model (non-TSW) and TSW mags are interchangeable.
Same part number.

My only answer is that S&W wanted the 40s&w to fit the 9mm double stack frame.

You're welcome!

John

The 59 mag will not insert into my 4006 model. Mag is too wide left to right. I tried several, all will not fit. But do go into the 4013TSW fine.

Rosewood

What I found interesting was that 5906TSWs do have the little cutout in the magwell for 40 mags, and will feed 9mm from them. Were 5906TSWs built on the same frames as the later 40s?

Yes, 59xxTSW models and 40xxTSW models share the same frame.

John

Very interesting, Dr. rosewood.

I have nine double stack 40s.

Six are TSWs, all '97 and later ship dates.
The 5906 mag fit every one.

Three are base models, two 4006s and a 4043.
The 5906 mag fit the 4043 ('97 ship date) and a 4006 ('06 ship date)

The 5906 mag would NOT insert (all the way) in to the 4006 with a 2/92 ship date.

I now wonder if your 4006 also has an early ship date?

Apparently, S&W was concerned about cross fitting of mags early on but then seemed to adopt a more cavalier attitude.

Anyway, thanks for bringing this up!

John