I was just measuring my various makes of USGI magazines and am amazed how much variation there is from magazine to magazine, even between those made by the same contractor. How these work in a variety of rifles is beyond my comprehension!

how much variation did you find ??

That's because it's NOT an exact science!

The tolerances are loose so that the system works in ALL environments, including Peanut Butter and Sand mixed in with your ammo at 20 degrees Farhenheit.

Try that with "Tight Tolorances" and see what I mean.

Tack

The tolerances are loose so that the system works in ALL environments

That would be a clearance.  You need a minimum clearance between parts.

What I think the original poster is getting at is the different widths of magazines.  The tolerances are ridiculous large.  On my Oly, about 25% of the mags can not be inserted.  They're just too tight.  About half can be inserted with some difficulty and are more difficult to remove.  About 25% can be inserted normally.  The differences in sizes is just too great for comfort.  It also sucks to have to sell-off magazines at a loss just to find a few that fit.z

I've found up to .020 difference when measuring front to rear and as much or more side to side.  I think this adds new meaning to the old story about staking your life on whoever happens to be the lowest bidder..... Some of mine lock up tight, some when locked sound like a baby rattle they move so much. I have Parsons, Okay, Sanchez, Center, Labelle. No Colt or Adventureline.  Mine are all pre 94, most are in like new condition.