Had the weirdest squib ever a few months ago in one of my M1 Garand rifles.
Somehow or another, the bullet lodged in the barrel just ahead of the chamber in such a way that it still allowed a gas path, still cycled the action on it's own, and FELT like a full power recoil. VERY FORTUNATELY, the next round presented into a failure to feed, which my Garand's don't do, so I examine the round by ejecting it and notice the bullet is pressed into the case mouth hard against the powder. Carefully trying to chamber another round let me know the barrel was most definitely obstructed. After unloading the rifle and using a steel rod the range had for just such an occasion, the squib round showed that it likely wasn't an under-powered round, but was probably seated at a bad angle, or possibly not crimped correctly, and there was lots of burning where the gas path was allowed between bullet and barrel.
I would have been upset, to say the least, if one of my Garands had met an untimely end to such a thing. If the bullet had lodged an extra 2 inches down the bore and felt like it did, I would have thought nothing of pulling the trigger again and who knows what could have happened.
Moral of the story, not all squibs feel soft. Recoil can be a good indicator, but whenever possible, make sure you're getting an extra hole in your target each time you pull the trigger.
XD Service .45ACP IWB in a Pro N8^2 Holster
-Know your gear, and stay safe