Vern Humphrey said:
Bullets don't tumble, they yaw. The 6.5x52 Carcano round and early 6.5x50SR Arisakas yawed just like the .30-06 and other rounds -- in fact the "Magic Bullet" that hit Kennedy high in the back and then went through to hit Connoly made a classic keyhole in Connoly's jacket -- 180 degrees of yaw. That was a Carcano round.
I can't comment on any specific instance like the Kennedy shooting (almost anything can happen in specific instances), but I have to disagree in general.
Bullets for use against heavy game like elephants and buffalo are made parallel-sided with round noses specifically because they will drive on in a straight line through considerable thicknesses of flesh and bone. Some of the early African hunters successfully used 6.5mm rifles (with long, round-nosed bullets) for this very reason. They also tried pointed bullets when they first came out but rapidly abandoned them because they wouldn't penetrate in this way, but travelled in unpredictable directions after impact.
It is also a fact that the British (who gained lots of experience at shooting people with the original round-nosed .303" bullet) found that its terminal performance was unsatisfactory becuase it drove straight through. That is why they adopted a deep, hollow-point bullet (following experiments at the Dum Dum arsenal) before that was banned by the Hague Convention. So they then turned to a pointed bullet, mainly to achieve better long-range performance but also because it was more effective.
The key fact is that, unlike round-nosed bullets, pointed bullets have their centre of mass well behind the mid-point of the bullet. As a result, their naturally stable attitude is to fly base-first. They are only kept going point-first by being spun by the rifling. At soon as they hit a dense medium like flesh they will turn over to travel base-first (which is slightly misleadingly but popularly known as "tumbling"). "Yaw" means that it is no longer travelling point first but not that it will necessarily turn over (APFSDS cannon rounds fired from rifled barrels tend to yaw for the first couple of hundred metres before settling down to fly point first, so they are less effective at short range).
Any pointed bullet will therefore turn over on impact, although the speed of this depends on the bullet design and construction. The .303" Mk VII had the centre of mass much further back than most, because of the lightweight tip filler, and therefore turned over quicker than most (the Germans were unhappy about this in WW1 and complained that it was against the spirit of the Hague Conventions).
Tony Williams: Military gun and ammunition
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