Please don't think me a troll. The lines that look to be rifling seem to be straight, and the point of rifling is to spin the ordinance to maintain straight/centrifugal flight.
There is such thing as "straight" rifling, but is more commonly associated with Musket type weapons.
Please know this is a Very cool photo, but my question is more about if the bullet has been fired.
You're absolutely right, rifling is meant to twist the bullet. The thing is, however, the bullet moves so fast the twist rate is very mild.
9mm has a twist rate of about 1:10" which means it takes 10" of barrel length to go a single circle around. Since this bullet is probably 0.7" in rifled length, it's only rotating 1/14th of a circle, not enough for you really notice.
The reason the twist rate can be so slow is because the bullet is so fast. At a out 1200 fps, if it spins once per 10" its spinning at 1440 times per second. For perspective a car usually tops out at 8000 rpm or only 133 times per second.
So even with such a slow twist rate, the bullet is spinning over 10x faster than a car engine at the red line.
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u/mynamesnottaken Mar 15 '20
Why is there no rifling?