That's a good point. Even the small base dies that I recommended if he's using 223 won't work if you're fudging around trying to get fairly snug shoulder fit.Where you run into issues is if it was fired in a rifle with a larger diameter web area of the case. Thats where it’s going to stick if it is. You can push the headspace back where needed but unless your die is specifically cut to resize the base small enough, you’re never going to get rid of that issue.
You can also get some false pressure signs from this even if it does fit, guys will call them clickers.
If it’s for a plinker, give it a go and see what happens.
For a precision rifle, If your a new reloader, I would avoid the headache of dealing with brass fired in another chamber, I’d also not even mess with mixed lot brass. You’re just setting yourself up for some head scratchers down the road.
I totally forgot about that.