So these are the same price at ammoman, and I'm about to order 500 or 1000 rounds.

Does it matter which I get?

Edited to add: Does one have less flash than the other, for example?  Or known to have smaller groupsings.  Or whatever else?

I like XM193 or Q3131a.

Either or.   Both are good.  I shoot both and I have no preference of one over the other.

Either, or.............

There have been some sporadic issues with blown primers lately on certain lots of Q3131A (see post by BRILLO). Members have not been able to fix on one cause, may be a combo of too much powder, improperly loaded or badly set primers, no/inadequate flash holes in the cases, and maybe rifles with tight chambers or other issues which place the rifle and shooter at risk with ammo that is at the high end of pressure specs.

Not saying don't buy Q3131A, just saying there may have been some manufacturing issues at IMI which are worth being aware of.

In contrast there have been no reports on XM193 since some very minor issues in some of the very earliest lots, and that may be the more statistically reliable product to go with right now.

I perfer Q3131A, but shoot both...

Get Q3131A........................its prettier!

If you load with stripper clips, consider getting XM193: the strippers slide right onto the cartriges as they sit in the box: you can't do that with Q3131A.

If you're a LULA man, "Q" is easier to dump out of its box than "XM".

My Bushmaster sees no noticeable difference in accuracy with either ammo: both are very good.