Ok, so maybe some of you will think this is stupid to ask, but here it goes.

Why Q3131 and not other 55 grain ball ammo from Remington or Federal? What does the Winchester ammo have that the others don't? I have a lot of Remington 55 grain ball ammo and am quite happy. What am I missing?

You're going to get the ammofaq homos all riled up!

Q3131 is M193 spec ammo.

The others are just regular .223 loads which are milder.  For plinking you can't go wrong with that ammo!

Quoted: What does the Winchester ammo have that the others don't? I?

1) Full sealers (primer and bullet).
2) Full military pressure
3) M193 bullet that will fragment.

Now if you just want to punch paper then by all means buy any 55gr round that reliably cycles your weapon and is accurate enough for you.  

Q3131/XM193 is seen as a good 'all purpose' round.  It fragments enough to be used for defensive purposes, accurate enough for informal target shooting, reliable enough for training classes, and cheap enough you don't mind blasting it when plinking.

You two have answered my question. Thank you very much.