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RPM of bullits


Subdeacon Joe

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Keeping it simple. A 1 in 12 twist. So, for every foot of travel the bullet makes one rotation. Assume a 2000 fps velocity. That means 2000 rps. Or 120,000 rpm. Amazing that they don't tear themselves apart.

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Keeping it simple. A 1 in 12 twist. So, for every foot of travel the bullet makes one rotation. Assume a 2000 fps velocity. That means 2000 rps. Or 120,000 rpm. Amazing that they don't tear themselves apart.

Some do. A light 40-45 grain varmint bullet in a .220 Swift or .22-250 can easily be driven fast enough to "vaporize" at the muzzle. It's due to the spin.

 

Good luck, GJ

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I can't link to it here from work, but in my photobucket account I've got a photo of a .45Colt bullet in flight. It's a streak several feet long, but if you zoom in a bit you can see a spiral pattern in the streak. I have to give Birdgun Quail credit for the photo.

 

Think of a bullet going 4000 fps, now were talking 240000rpm.

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Keeping it simple. A 1 in 12 twist. So, for every foot of travel the bullet makes one rotation. Assume a 2000 fps velocity. That means 2000 rps. Or 120,000 rpm. Amazing that they don't tear themselves apart.

Some light varmint bullets can, in fact, wrend themselves apart, if fired through a barrel of excessively fast twist.

 

I remember it once was popular for antigunners to quote such figures and then speak of bullets ripping through flesh like buzzsaws. A bullet travelling at such velocities only makes 1 or two complete rotations while passing through a torso, depending of course on the rotundness of the target. Figures don't lie, but liars sure know how to manipulate figures.

 

 

EDIT Do I really type that slowly? :lol:

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Yep...I know that some do go "POOF!" upon exit from the muzzle. People handloading and pushing the envelope. I watched one guy at the range testing some he had loaded. All was going well and then he couldn't hit the paper. Set up a target frame at about 5 yards and hung a 28 x 40 parent sheet on it. Looked like he had fired a .22 bird shot into it. Figured he had pushed it just a little bit too hot.

 

My point was that at that RPM that any of them hold together is pretty impressive design and quality control.

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Okay, Joe... now my head hurts. :(

 

Here I was, sittin' here ponderin' the quandry of getting solid copper boolits to "stabilize" in rifles with the slower twists established for lead or lead core pills... and now... Dang! :wacko:

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Here's an interesting article on the topic => http://bulletin.accurateshooter.com/2008/06/calculating-bullet-rpm-spin-rates-and-stability/

 

And the quick version of the formula: MV X 720/Twist Rate = RPM

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Yep...I know that some do go "POOF!" upon exit from the muzzle. People handloading and pushing the envelope. I watched one guy at the range testing some he had loaded. All was going well and then he couldn't hit the paper. Set up a target frame at about 5 yards and hung a 28 x 40 parent sheet on it. Looked like he had fired a .22 bird shot into it. Figured he had pushed it just a little bit too hot.

 

My point was that at that RPM that any of them hold together is pretty impressive design and quality control.

I've seen similar.

 

In his case, the bullet was coming apart more than 25 yards out (He started out that close since he was rezeroing his rifle) but before it reached the 100 yard targets. He got so frustrated that he walked down the firing line and asked me to spot for him. The only reason I saw what was going on was because he was firing from the prone position and I stayed standing (I was really watching for dust jumping up from bullet impacts to get a ball park of WHERE they were going) instead of getting down on the ground and using his spotting scope. It looked like a little gray puff of smoke and it took me a couple shots to connect the dots and figger out what it was.

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I've seen similar.

 

In his case, the bullet was coming apart more than 25 yards out (He started out that close since he was rezeroing his rifle) but before it reached the 100 yard targets. He got so frustrated that he walked down the firing line and asked me to spot for him. The only reason I saw what was going on was because he was firing from the prone position and I stayed standing (I was really watching for dust jumping up from bullet impacts to get a ball park of WHERE they were going) instead of getting down on the ground and using his spotting scope. It looked like a little gray puff of smoke and it took me a couple shots to connect the dots and figger out what it was.

 

Back in 1988 at the Railhead shoot in Buckskinner Park, Williams AZ. I was shooting across the lake at a long range target. I was shooting a Remington Rolling Block in 7mm Mauser. I had handloaded some really fast and hot lead bullets, thinking flat trajectory. WRONG. My bullets were not making it to the target 350 yards away. They were coming out of the barrel and disintegrating and splashing in the lake. It took a few rounds to discover what was happening.

 

Greybeard was spotting and focused on the target, not on the lake. Bystanders were commenting on the little splashes in the lake at each shot. The cleaning rod had slipped out and was sticking beyond the muzzle 3-4 inches It was covered with lead smear by the exiting rounds. They asked what powder and velocity I was at? I told them and we figured that the lead bullets were traveling above 3000 fps(too fast) duh! I have since slowed the loads to a moderate level and learned a thing or three.

 

Big Jake

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When you get to hot loads with leads bullets, don't you also get to the problem for which gas checks are needed?

 

Yep. I use a gas checked lead bullet now and keep the velocity to a modest 1300-1500fps.

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When you get to hot loads with leads bullets, don't you also get to the problem for which gas checks are needed?

Yep. I use a gas checked lead bullet now and keep the velocity to a modest 1300-1500fps.

I agree you would run into a variety of other problems before you could push a lead bullet fast enough to disintegrate. It was more a hypothetical question.

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