Can someone tell me what happened to this bullet?

[ButterBean]

And at that speed it may have very well deflected and tumbled

 

[P7M13]

It's a bullet that identifies as a banana.

 

[6mm06guy]

What is the minimum opening velocity for that bullet?

I haven't found an exact number yet, I was sent to maker by the guys at hammer bullets under there recommendation that they would open under 800 fps

 

[JasonAL]

You said it was your 3rd subsonic deer. What other cartridges, projectiles were used on those?
I would also actually check the twist on the barrel as it might be slower than what it's marked to be.

Which picture was the entry wound? One looks like it penetrated sideways if that's the entry.

 

[med358-boise]

After skinning the deer, I believe it skinned the top edge of the scapula and turned, I don't completely disagree that the bullet may be slightly under stabilized. Maker offers several more options like the 190 gr. I may test next year, but I spent so much time working this up for him and he did a heck of a job this year.

I can't help but wonder if I shouldn't change the bullet if the overall concensus is that the bullet tumbled.

I just ran your numbers thru 2 stability calculators (Berger & JBM) using a 1 in 8 twist which is standard for the 300 BlkOut and that bullet is very stable per the formulas. I used 50 deg F and 1000 t for altitude

You have a single data point and based on the pic of your son and the deer massive internal damage. I wouldn't change anything. I would add that if the first pic of the carcass is an entry wound that hole looks elongated but that could be just the angle of the photo.

Rig your self up some homemade test media - plywood box stuffed with wet phone books (not perfect, but not bad either) and see if you get any weird results.

 

[ButterBean]

And with everything that's been said it very well could have just been a fluke