What are bologna and hotdogs really made of?

I doubt you will find a specific ingredient list that identifies particular cuts or parts of meat.

As an example, here is the ingredients for Oscar Mayer bologna: Mechanically Separated Chicken, Pork, Water, Corn Syrup, Contains Less Than 2% of Salt, Sodium Lactate, Flavor, Sodium Phosphates, Autolyzed Yeast, Sodium Diacetate, Sodium Ascorbate, Sodium Nitrite, Dextrose, Extractives of Paprika, Potassium Phosphate, Sugar, Potassium Chloride.

Similarly, you can probably look up the ingredient lists for other brands and products.

Making an emulsified sausage (hot dogs, kielbasa, bologna, mortadella, etc.) from scratch is not that difficult. You would probably not want to make it exactly like these companies do. They are mass producing and need to ensure shelf life, as well as safety. There are a lot of things on that ingredient list above, for example, that you would not need if making this at home. Additionally, these companies weigh quality against cost efficiency. At home, you would likely use higher quality ingredients. Although, there is an argument to be made about the parts of the animal that are desirable vs. not. This could just be your preference. I'm not sure how you are defining "premium." I assume that in general, the parts of the pig, cow, and chicken, that can be sold at higher prices are not used to create emulsified sausages.

In the end, you probably get what you pay for in terms of quality.

OP here answering my own question after doing some research.

First off, here's an excerpt from this USDA resource:

https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/meat-preparation/hot-dogs-and-food-safety/CT_Index

Byproducts, Variety Meats "Frankfurter, Hot Dog, Wiener, or Bologna With Byproducts" or "With Variety Meats" are made according to the specifications for cooked and/or smoked sausages (see above), except they consist of not less than 15% of one or more kinds of raw skeletal muscle meat with raw meat byproducts. The byproducts (heart, kidney, or liver, for example) must be named with the derived species and be individually named in the ingredients statement.

So hot dogs and bologna can indeed contain organs, but they must be named on the packaging. Therefore, if you don't see heart, kidneys, brain, or other organs listed in the ingredients then it's safe to say the product is devoid of those parts. In this case, the product should consist entirely of skeletal meat, though this will be mostly trimmings.

Secondly, it also comes down to how the meat is removed. See below excerpt to this USDA resource:

https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/food-labeling/meat-and-poultry-labeling-terms/meat-and-poultry-labeling-terms

MECHANICALLY SEPARATED MEAT is a paste-like and batter-like meat product produced by forcing bones with attached edible meat under high pressure through a sieve or similar device to separate the bone from the edible meat tissue. In 1982, a final rule published by FSIS on mechanically separated meat said it was safe and established a standard of identity for the food product. Some restrictions were made on how much can be used and the type of products in which it can be used. These restrictions were based on concerns for limited intake of certain components in MSM, like calcium. Due to FSIS regulations enacted in 2004 to protect consumers against Bovine Spongiform Encephalopathy, mechanically separated beef is considered inedible and is prohibited for use as human food. However, mechanically separated pork is permitted and must be labeled as "mechanically separated pork" in the ingredients statement.

So the difference between the beef and chicken and pork products is that chicken and pork can be mechanically separated, but beef cannot. What this means is that the chicken and pork product will contain whatever was on the bone at the time of separation which includes not only skeletal meat, but also skin, connective tissue, a regulated quantity of bone, and even blood vessels. That's not to say that the beef product is guaranteed to be devoid of these parts, but it's far less likely since the separation is manual and, therefore, more discriminate.

I think the differences between the separation processes also explain why the beef product is significantly more expensive since there's less automation to reduce costs.

Anyway, I will be marking this as answer in a few days unless anyone can point out any errors in my research.

I can't speak for pork and beef but as far as chicken goes...

I've worked in a chicken processing factory and we did prepare a "slurry" for hot-dog/bologna or whatever else they put it in. It was mostly the leftover meat & fat from the carcass that we couldn't easily remove. Carcasses were chopped up finely then separated by a centrifuge machine into "meat" and "bones". We'd sometime also throw in trimmings if we didn't have enough orders for nuggets but no organs ever went in there.

I don't know about the slurry quality but we did sell the breasts according to the age and quality of the chickens we'd get.