I was recently asked why bologna rises in the center when fried. Does anyone out there know why EXACTLY that is so I can tell my friend. Thanks 
This is a deep question Squirlgirl. I suspect that no one has come up with the definitive answer, unless it is some poor food-science grad student with a thesis advisor from hell.*
That said, I think the warpage of cooking bologna is caused by factors which are similar to those that produce coffee rings.
A cooking round of bologna loses fluid and shrinks. However the rate of dehydration is greater around the perimeter than it is toward the center. Water, grease or whatever, coming out of the perimeter of the bologna is free to evaporate, or spread over the pan, while that which comes out of the bottom/center of the meat is stuck under the sausage where it cannot diffuse, and liquids coming out on top of the sausage are insulated from heat by the food itself. These differences force the perimeter of the meat to shrink more rapidly than the central portions; and when that happens, the central region must buckle, or defy Euclid himself. With the two possible buckling directions being up or down, the bologna bubbles up because some of the water trapped under the sausage is turned to steam which exerts an upward force.
*The kind of advisor who makes you do research like this:
I get the same effect when I microwave deli-sliced summersausage. Except I usually get it to curl up, making a nice concavity to hold the poached egg! Throw some cheese, hot sauce, and marmite in there, put it between an english muffin, and you’ve got a great sandwich!
Otherwise I believe Squink is right. The outer circumference of my summersausage is always cooked more than the center.
The skin shrinks faster than the meat? Does this also happen with skinless bologna?
Nobody said anything about the skin. Squink stated that the outside cooks faster because it’s not insulated, and water can evaporate more quickly because it can go directly into the air, and does not have to diffuse through more balogna.
Yes, skinless bologna does this too.
Besides that I have nothing to add to this thread, except that I’ve fried a lot of bologna and I’ve never really thought about why it does this, so thanks for asking such a thought provoking question.
P.S. I must mention as a pizza gourmet that pepperoni does this as well, albeit on a much smaller scale. Pepperoni bows in though, like a bowl, which seems to go against Squink’s explanation that the upward force of steam causes it to bow out.
Sure, there are all sorts of confounding factors: the diameter of the disk, its thickness and rigidity, granularity of the sausage, differential drying of the outside during curing etc. etc. Floppy bologna with little rigidity and minimal graininess is likely the simplest case, and even that will sometimes bubble down or buckle into ying-yangy bumps. As I implied initially, it’d probably take a grad student chained in hell years to unravel all the possibilities.
A pair of kitchen scissors makes the whole problem moot.
Because it’s smaller? Because the bowl shape keeps all the delicious pepperoni grease in one place?
Since it’s smaller it can’t develop the same force with an equal amount of pressure. Also, the pepperoni is “less floppy” (I don’t feel the word rigid is appropriate), so it can support the initial upward curl more readily.
How do I get one of those gigs? (assuming I get to eat the samples)
Bologna…skin?
I’m confused. Since when does bologna have skin? I’ve only ever seen bologna that’s just bologna, or else in a wax rind. Never with a skin…
Bologna sold in your grocer’s deli case has an outer layer that is slightly different in texture from the rest. Visible here
Where’s the Miracle whip and mustard? 
My question was, why only one slice of bologna? Around these parts we layer three bologna slices with two American cheese slices, alternating.