What is the physical limitation of using blood bending (hemokinesis) to make bullets with your own blood?

Question

Recently, I have considered making a character who is able to use what is essentially blood-bending, otherwise known by its more formal name of hemokinesis.

The problem is that this ability has one clear limitation when you are drawing from your own source of blood. There is only so much blood in the human body that can be used before the person kills themselves by using it all.

According to the Blood Calculator I found online (https://www.thecalculator.co/health/Blood-Calculator-67.html), the amount of blood this character should have would be approximately 4.08 liters. Female-170cm tall-65 kg.

This character is able to create and fire bullets of her own blood telepathically. Let's say that a bullet of blood is roughly cylindrical and has an approximate length of 3 cm and radius of 0.5 cm. Using the area formula of a cylinder I get that 3 * 0.5^2 * pi cm^3 worth of blood was used for one bullet. This is approximately 0.75*pi or 2.356 cubic centimeters worth of blood.

Considering the body weight and height of my character, approximately how many bullets of blood would she be able to create before she started to face serious health consequences due to her ability?

To clarify, I am specifically asking how many bullets of blood she would be able to extract from her own natural stores before she faces grievous health problems as a result of what is missing.

Edit: We will assume a battle using this power could be anywhere from 15 minutes as a low estimate and as much as 2 hours in length as the high estimate.

This character has had this power since the age of twelve. She is 19 now. The longest she has gone without using it is three months. The longest successive use of her power was at least one battle per day over a two-week timeframe. Her average is at least four to five major battles every month of every year since she got the power, leading to a total of about 400 battles in her lifetime.

Edit2: To answer a question about reload time I would say she can make a new bullet every 1-3 seconds and she can sustain each individual bullet she creates for as long as she needs them.

Edit3: I have erased the section about 2% loss as I have deemed it irrelevant.

Answer 1

"How much blood can this patient afford to lose..."

This was a trick ~ not trick question a wise surgeon used to ask medical students. It's a trick question because, indeed, a person can stand to lose some blood without long term effects. It's a not trick question because we're not really designed to lose blood, and it doesn't take a lot of blood loss to cause problems.

Without knowing a lot of specifics about your character (and thus risking a rather curious case of blood related story based questioning) I'd stick with some generalities.

People donate blood all the time, and people get cut and bleed all the time. Since people don't regularly die after giving a unit of blood, there must be some amount of padding. Since this varies by person, and it's not a quantity you ever want to discover about yourself, I'm going to remain well on the safe side of the line.

There are several levels of hemorrhage. 1 through 4, according to this article.

Class 1 is a blood loss less than 15% of the total volume. Donating blood easily falls in this category. A typical donation is about 10%, so about 400cc for your character. That's 170 bullets.

Class 2 is a blood loss of 15% to 30% of total volume. This is survivable, but not an ideal situation to be in. She'll feel weak and probably a little light headed. Not a good situation for a warrior to be in during a fight. 30% is 1200cc or 509 bullets.

Class 3 is a blood loss of 30% to 40% of total volume. She'll need a blood transfusion if she pushes herself this far. 40% is 1600cc or 679 bullets. She will most likely fall unconscious at this point.

Class 4 is a blood loss of over 40% of total volume. This is pretty much fatal without immediate access to critical intervention. The loss is so great that body systems can no longer be supported, including the brain. Things just shut down and she'll die. If your character were able to squeeze out a few more bullets, perhaps as a last ditch effort to go down fighting, she might be able to use 50% of her total volume for bullets. That's 2000cc or 849 bullets.

I'm disregarding the 2% loss rate as irrelevant. The blood is gone from her body, so it doesn't really matter if some ends up on the floor or ends up on the wall next to her target.

Conclusion: Hemokinesis is an interesting idea, but from a tactical / military / warrior culture perspective, it's really dumb! Blood isn't something you want to willingly give away, especially in a fight, unless she's really at the ultimate extremity and she's going to die any and has made the choice to take out as many enemies as she can.

I'd argue that your blood blasting warrior girl can "safely" expend no more than 170 bullets during any engagement. Whether that's a fifteen skirmish or a battle lasting a week. In the extreme, and if she's a valuable asset, then I think it could be argued that she could double that over a period of time and that she should be made to rest and given volume replenishment treatment (IV fluids).

She could survive more, but that would be a waste.

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It was always a pleasure to watch as said medical students tried to follow the same calculations you did to arrive at a particular number. The answer to the question, by the way, is "none".

Answer 2

Blood loss aside, I would question the properties of your 'blood bullet' itself.

A liquid 'bullet' would simply splash against a target, and wouldn't damage the offender in any measurable way. If you hit them in the eyes or mouth you could inflict blood transmissible illness, but I don't know if that's what you're after.

While that bullet is in flight, if it's reaching supersonic speeds it would be reasonable to assume that the leading edge could heat up above 100 degrees C due to frictional forces in the air (this assumption is loosely based on aircraft like Concorde which regularly saw temperatures of 100+ on the nose cone when in flight). While the blood bullet has a smaller surface area and likely would undergo less heating during flight, it would still likely evaporate fairly quickly, and if not the friction of the air would probably atomise the fluid itself anyway.

If the blood bullet is frozen, however, it may have a chance of not evaporating before hitting the target. I believe mythbusters tried this concept with a water ice bullet, however from memory they had issues with it shattering in their barrel when firing. Your magic blood bullet likely won't have this problem, but it may also shatter when impacting the target unless it's travelling at an extremely high velocity - in which case it would have problems with melting due to friction with the air as mentioned above.

That all being said, if the bullet remains magically entwined during it's flight and is able to retain all it's properties up until the point of penetration, then these comments are moot.

Answer 3

I don't know if it was an edit in the original post after 'elemtilas' provided their detailed answer, but it looks like the 2% loss isn't as insignificant as assumed. From the post, I understand that the blood that's used for a bullet returns to the character's body once the bullet has done its work/damage, with a 2% loss.

Using the numbers from the aforementioned answer, if we assume the bullets are made and used one by one (to provide them with the psychokinetic energy required to overcome the limitations mentioned by 'Aaron Lavers'), only 2% of the volume of a bullet is lost for each, so the amounts can be multiplied by 50 with about the same side-effects as already described:

• 170 --> 8500 bullets with relative ease/safety
• 509 --> 25450 bullets with the effect of becoming weaker and light headed
• 679 --> 33950 bullets after which she'd need transfusions
• 849 --> 42450 bullets after which she bites the dust

If using your enemies blood is also an option as suggested by 'AmiralPatate', you're getting even closer to an unlimited amount than already suggested.

Answer 4

Unlimited

This outrageous answer comes courtesy of the calculation having already been made correctly, thus I'm left with the other obvious answer that your problem is using your blood when you can use...

THE BLOOD OF YOUR ENEMY!

There wasn't any qualification that using other sources of blood was forbidden after all, so this is still technically correct.

Now, to be perfectly accurate, the answer isn't "unlimited" because you will likely run out of enemies. But if you run out of enemies, you also don't need bullets, so practically unlimited.

Taking the calculation from @elemtilas, if 50% of a human's blood is 849 bullets, I think we can conservatively estimate that you could take a thousand bullets out of every enemy you turn into a corpse on average.

This assumes you can use the blood of people who no longer need it. If you could use the blood of live creatures other than yourself, at that point, you might just drain them of blood and skip the bullet-making part. If you can't do neither, obviously just buy a gun.