What would happen IF you shot a .25-06 round out of a .30-06 chamber and barrel?

I went to the rifle range to shoot my .30-06 yesterday. I took a box of partially used (10 fired, 10 non-fired) Remington Core-lokt ammo in .30-06 and a second full box of Remington Core-lokt ammo in what I thought was .30-06 ammo. As I picked up this full box to load my rifle, I noted that the end tab identified the ammo as .25-06. OK. No harm done. This is what you're supposed to do -- check your ammo before you load it into your rifle. I did that. I avoided shooting the wrong ammo. If I had not done this and opened the box and started to pull out the cartridge to load . . . chances are I would have taken note of the distinct difference between the 100 grain .25-06 rounds and the 180 grain .30-06 rounds I was shooting. Again, no harm.

The question is, what if I had not noticed the error and shot the .25-06 in the .30-06? Because the cartridge casing of these two are essentially the same (.25-06 is a necked down .30-06), the cartridge would have no doubt fed normally out of the magazine and into the chamber. I would guess nothing dramatic would have happened -- no exploding barrel. My question is what WOULD have happened, or what are the multiple alternative things that might have happened?

I settled on shooting Hornady Custom ammo in my .25-06 years ago, because it shoots accurately in my rifle; and settled on the Remington Core-lokt ammo in my .30-06 years ago, because it shoots accurately in my rifle. Hence, I associate the distinctive Hornady Custom ammo box with my .25-06 and the distinctive Remington Core-lokt ammo box with my .30-06. It happens, when I was first evaluating commercial loads in my .25-06, I bought some boxes of Remington Core-lokt .25-06 . . . which explains why I have the ammo and also why I wasn't more careful at the house packing my shooting bag before going to the rifle range, in case anyone wants to know. A little too much "auto pilot" and not enough attention to detail. Fortunately there are many opportunities along the way to check oneself, and the later check worked.