Am I supposed to be able to do a dead hang while griping the bar when doing chin ups? My wrists/forearms don't go around enough to face me with my arms straight overhead. Is this a flexibility issue on my end or just a straight "the human body isn't meant to move that way" issue?
I can dead hang with a neutral grip or in pullup position.
I would say its probably just a human body thing. I can't speak for anyone else but I can't dead hang with that grip either, only neutral or palm facing out 
I used to have the same problem, I just kept working at it
and doing some stretching for my wrist, forearms & biceps.
I have no problem doing them now, just be persistent and you'll get there.
Good to know. I'm relatively flexible in certain directions. But where I'm not flexible, I'm so stiff that I just feel a "hard stop" most of the time so that I don't know if I've just hit the end of ROM and forcing will lead to hyper extension, or if I'm just not flexible.
What are some good wrist, forearm and bicep stretches?
12ealdeal - Not sure I am understanding the issue.
Is a dead hang simply hanging, fully extended, elbows locked?
Meaning my palms can't face me when my arms are straight over my head. They can face each other, or face away from me. So if I try to do a chin up I'm never in a dead hang, I just go 2/3's of the way down and then back up.
This is extremely common, and almost certainly has little to do with bicep or forearm flexibility. (Leigh has claimed in the past to have a mobility issue in this regard, which would be something not at all "normal.")
In general the internal humeral rotators have poor flexibility.
To test this:
1. get a broom stick.
2. Sit up against a wall. Get your tail bone right up to the wall. Tuck your heels in close to your butt (they should be just about touching). Flatten your back against the wall, and keep the back of your head on the wall. It should look like you're at the bottom of the deepest A2H squat ever. If you can't get into this position, you have bigger problems to worry about that chin-up form.
3. Hold the stick in a chin-up grip (palms facing you). Put the stick up against the wall just over your head.
4. Slide the stick up the wall as far as you can. Notice that your elbows begin pointed in front of you. Notice that as you go up your elbows start to veer outward. You will reach your limit because your elbows will veer out so much that pressure will develop at your wrist.
5. Now switch to a pull up grip (palms away). You will probably be able to go all the way up the wall this time, but your elbows will be winged out. With a pull up grip, start with the broom stick just over your head again, but keep your elbows pointed forward. Slide the stick up the wall, and do NOT let your elbows veer outward AT ALL. Notice that there is no pressure on your wrists at all, but you can still only go part way up the wall.
I can take a video of this if it needs any clarification.
Yup, you have issues that most people do not share.
Leigh - There is no part of that stick grabbing that I'd be able to do
We're in the same boat. I'm in the "bigger problems" category. I have poor hip/knee/ankle flexibility. When I go ATH for squats my bottom is just a bit past parallel. Can't sit "seiza" for long periods either since my butt never touches my heels.
vermonter - This is extremely common, and almost certainly has little to do with bicep or forearm flexibility. (Leigh has claimed in the past to have a mobility issue in this regard, which would be something not at all "normal.")
In general the internal humeral rotators have poor flexibility.
To test this:
1. get a broom stick.
2. Sit up against a wall. Get your tail bone right up to the wall. Tuck your heels in close to your butt (they should be just about touching). Flatten your back against the wall, and keep the back of your head on the wall. It should look like you're at the bottom of the deepest A2H squat ever. If you can't get into this position, you have bigger problems to worry about that chin-up form.
3. Hold the stick in a chin-up grip (palms facing you). Put the stick up against the wall just over your head.
4. Slide the stick up the wall as far as you can. Notice that your elbows begin pointed in front of you. Notice that as you go up your elbows start to veer outward. You will reach your limit because your elbows will veer out so much that pressure will develop at your wrist.
5. Now switch to a pull up grip (palms away). You will probably be able to go all the way up the wall this time, but your elbows will be winged out. With a pull up grip, start with the broom stick just over your head again, but keep your elbows pointed forward. Slide the stick up the wall, and do NOT let your elbows veer outward AT ALL. Notice that there is no pressure on your wrists at all, but you can still only go part way up the wall.
I can take a video of this if it needs any clarification.
So what am I supposed to be testing here? Is this a stretch or am I just supposed to go "yup, sure can't do this?"
nottheface -Leigh - There is no part of that stick grabbing that I'd be able to do
We're in the same boat. I'm in the "bigger problems" category. I have poor hip/knee/ankle flexibility. When I go ATH for squats my bottom is just a bit past parallel. Can't sit "seiza" for long periods either since my butt never touches my heels.
Leigh can't grab anything with a supinated grip if i read him correctly. His issue is mobility, yours seems to only be flexibility.
nottheface -vermonter - This is extremely common, and almost certainly has little to do with bicep or forearm flexibility. (Leigh has claimed in the past to have a mobility issue in this regard, which would be something not at all "normal.")
In general the internal humeral rotators have poor flexibility.
To test this:
1. get a broom stick.
2. Sit up against a wall. Get your tail bone right up to the wall. Tuck your heels in close to your butt (they should be just about touching). Flatten your back against the wall, and keep the back of your head on the wall. It should look like you're at the bottom of the deepest A2H squat ever. If you can't get into this position, you have bigger problems to worry about that chin-up form.
3. Hold the stick in a chin-up grip (palms facing you). Put the stick up against the wall just over your head.
4. Slide the stick up the wall as far as you can. Notice that your elbows begin pointed in front of you. Notice that as you go up your elbows start to veer outward. You will reach your limit because your elbows will veer out so much that pressure will develop at your wrist.
5. Now switch to a pull up grip (palms away). You will probably be able to go all the way up the wall this time, but your elbows will be winged out. With a pull up grip, start with the broom stick just over your head again, but keep your elbows pointed forward. Slide the stick up the wall, and do NOT let your elbows veer outward AT ALL. Notice that there is no pressure on your wrists at all, but you can still only go part way up the wall.
I can take a video of this if it needs any clarification.
So what am I supposed to be testing here? Is this a stretch or am I just supposed to go "yup, sure can't do this?"
It will show you that your flexibility problems have nothing to do with your wrist, forearms, or biceps.
Any suggestions on how to fix it?
Stretch every day instead of never.
vermonter - Stretch every day instead of never.
So maybe I missed something in your post. What should I be stretching?