I'm experienced with mechanicals and fixed blades. I've taken 55 deer with bow and arrow with a majority being with various mecnahicals. (Mostly does and small bucks)

I've used Punchcutters, Rockets and Wasp Jak-Hammers all in 75 grn.

I've also used various fixed blades Thunder Head 125's, Wasp cam-lok's, Satelites and Muzzy 75's.

I've hit the shoulder blade several times ( with both types of heads )and lost several deer in my 30 years hunting. That's nothing to be proud of but it happened and I admit it.

When it happened it was exactly as you said. A loud smack sound, very little penetration and very little blood trail. So based on my experience, that is what you did. I wasn't there but you described to me what I've experienced.

As far as a Mechanical not opening and causing the arrow not to penetrate, I doubt that. I'll tell you why.

A few times I had hit deer with Rocket Miniblasters. As most people know, after one shot blades get bent, broke and twisted. They aren't very durable. Anyway I hita doe and found my arrow. The head was in bad shape with 2 blades broke off. As I was tracking the doe, it stood up about 20 yds in front of me. I knocked the arrow I just shot and shot it again, broken blades, bloodand all. It did a complete pass through. The first shot only got 1 lung while the second got both.

A similar thing happened two more times without a complete pass through but the broadhead was sticking out the other side.

Ribs are soft bone compared to leg and shoulder bones. I don'tbelieve a rib from a whitetail can stop arrows, even without blades.

Like I said , I wasn't there. You were. Just giving youmy opinion based on my experience.