Maybe the bullet struck be leg expanded and leg bone and the fully expanded bullet tore into the near side chest wall. It then pealed back and exited the offside in its smaller final diameter. We really can't tell without the bullet but I have seen it a lot with bullets on close shots where they too quickly expand but should expand more traditionally at longer ranges.

How far did the deer go after being struck?

 

Yes. At close ranges with cup and core style bullets, any bone can sometimes cause the jacket to peel off of the core. I saw it last on a 308 at about 75 yards. There was a very small exit and a massive entrance. Little blood trail, and the buck made it about 55-65 yards before piling up. Massive internal bleeding. Bullets do funny things sometimes. I had a shot from Hornady LE do a similar wound at 25 yards on a neck shot, but he was DRT.

 

It went about 60 yds after being shot, the bottom half of the heart was nearly torn in two by whatever part of the bullet continued through it.
Overall it was a perfect hit in the heart,
I lost a small portion of leg/shoulder meat, but plenty of meat remaining to fill the freezer.

 

any chance it hit something...even a twig...before impact!?

 

Same thing happened to me using my .308 Win with the Nosler 150gr Ballistic Tip. Shot a buck running at about 50yds. He "mule kicked" and kept going for another 30yds. Bullet hit
the right shoulder, exited shoulder continuing into the ribs under the shoulder. I could put my fist through the hole in the ribs. Destroyed the lungs and exited the off shoulder. The
exit hole was about 1/2" in diameter. Called Nosler about the small exit hole compared to the size of the onside hole through the ribs under the shoulder. Nice gentleman at Nosler told
me that it happens sometimes if the bullet has exhausted most or all of it's energy before exiting. It made sense to me as the 1/2" exit hole was about the same diameter as all the
.30 caliber bullets recovered by me from deer kills with the 30-06 and .308 Win.
358 Win

 

Check on You Tube for shooting into gelatan blocks. In slow motion you can see that the wound channel is larger at the entrance than it is at the exit. I think that is has to do with the amount of compressed air that surrounds the bullet and follows into the wound. As the bullet slows the compressed air expands and vents off.

 

Updated original post with photos. maybe someone might be able to see better what happened.

 

With the Remington Core Lokts in 200 grain for the 35 Reminton.... my enter and exit holes are about the same size. My wife shot a doe this weekend at 70 yards... you could tell from blood trail she was bleeding on both sides, found her within 60 yards. When hit in a good kill location, the deer don't go any further than about 60 yards. Im out of the Remintons and are now shooting the Hornady Leverlution. Shot doe at 50 yards in neck and folded her right there.... no blood trail

 

Is it dead? Don 't fret the details.