This is correct. 50% shear force is in no way possible with that setup.
OP, I'd recommend this for the wall, and use it to hang jackets or something when not in use:
I don't recommend them. Get a bar drilled to the wall, that will hold a lot better. Something like this.
I got this one from Amazon. Great price and its super sturdy once screwed into the studs. Ive been using mine consistently for the last 5 months with no issues. I like how this bar allows you to do chin ups, pull ups, wide grip, and parallel grip. Also I use it for hanging leg raises. Highly recommend!
I wanted a sturdy pullup bar that mounted above the doorway. This way i can close the door without removing an "iron gym" style pullup bar.
I bought the below pullup bar, found it for less than $20, either walmart, ebay or amazon.
Ditch the crossbar, go to home depot and get 3/4" iron pipe for $12, long enough to span the entire doorway. Find the studs, secure the mounts to the walls then cut the iron pipe to fit.
Also bought rings to hang from it for dips.
Next up is gravity boots.
I'm building a nice little home office gym.
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You don't mention the other equipment you have or style of training. Based on what you've posted i'm assuming you're interested in pullups, leg raises and maybe dips.
I put the below pullup bar in my home office for some quick sets. I ditched the crossbar and instead bought an iron pipe from home depot and drilled and secured it to the support members. Iron feels better and being able to choose the width of my supports let me mount it to the studs above a doorframe with lag bolts. It was another maybe $20 in hardware (bolts and pipe).
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I also bought gymnastic rings to hang from it to do dips and L-Sit. Rings and straps can be had for $20-$30.
This isn't my main strength gear, so i went cheap. If this will be your primary strength gear you may want to go with better quality.
As a wise Joe Rogan mentioned in one of his YouTube videos, for the exact problem that you are experiencing using a door frame Pull-up Bar it is a danger to self and physical property. Invest in a Wall Mounted Pull-up Bar and anchor it to Good Strong Wall Studs. Work hard yet work safe. https://www.amazon.com/Yes4All-Wall-Mount-Chin-Bar/dp/B019H3C8L4/ref=mp_s_a_1_6?keywords=pullup+bar&qid=1564487086&s=gateway&sr=8-6