So standard glossy photopaper seems to be 52+lb.
The thin two sided paper I got was 32lb. Still a bit thick for magazines.
The next size down seems to be 20lb and that is just standard copy paper, none of which I could find in semi gloss.
I have no idea what it means as obviously it's not the weight of these fifty sheet packages, etc.
Just FYI
I can help with this!
First, a common language when talking about paper: paper weight is deeply weird in the US. US "pounds" refers to the weight of a stack of 500 sheets in its full made size, with that original size dictated by paper type - Bond (what copy paper is rated with) is, when first made, a wildly different size from Text, which is different from Cover, which is different from Card. So the same thickness of paper, made in different large sizes, will have different weights depending on its intended use,
and those weights will differ even if the final paper size is the same 8.5x11.
Europe, however, uses the mighty convenient "grams per square meter", which is the same weight rating regardless of the original paper size or its intended use.
A few benchmarks:
Cheap copy = 20 lb bond / 60 pound text / 80 gsm
High end copy / lower weight photo = 32 lb bond / 120 gsm
High weight photo = ~52 lb bond / 200 gsm
(Fountain pen nerds and paper nerds like myself tend to prefer paper rated in the 90-120 gsm range.)
From a quick bit of research, most magazines will aim around the 100-120 gsm range, or about 28-32 lbs bond weight. However, they're not printing on photo paper, they tend to do offest (big-batch) printing on what I'm guessing is a specially coated paper type.
In other words, difficult to reproduce at home, or even at a Kinkos.
If you can, I'd try getting a sample of some really high quality 28 or 32 lb, coated printer paper and see how your prints look on it.
I'd be curious to see what your process is and how it turns out!