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PostPosted: Sat Aug 04, 2018 9:17 pm 
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Joined: Fri Jul 27, 2018 10:34 pm
Posts: 284
Location: Bowmanville, Ontario
.22 pellets. I certainly learned about pellet instability from Ted Bier. His slow-mp cameras really open up the world of seeing what's really happening. What he doesn't really ever get into, or that I've caught anyways, are remedies for the spiraling.

I've been noticing that depending on my distance to the target in getting either grouping in different areas or accuracy is just all over.
Spiraling may or may not actually be the problem, but I'm interested in a discussion about the topic, none the less.

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Fully rebuilt Benjamin .22 classic
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PostPosted: Sat Aug 04, 2018 11:56 pm 
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Joined: Mon Aug 26, 2013 12:19 pm
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Location: Alvinston, Ontario
Thought he just slowed the gun down a little? Spiraling was due to shooting too fast.

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PostPosted: Sun Aug 05, 2018 12:08 am 
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Location: Coalmont BC
This "spiralling" or "corkscrewing" is called "Dynamic Instability".... It is complex, but one of the key causes is spinning too fast.... A pellet can be dynamically stable when shot but because it loses forward velocity faster than it looses RPM, as it goes downrange it can become dynamically unstable as the range increases....

There are two solutions if this problem exists.... You can either slow the pellet down, which reduces the RPM, and hence the relationship between its forward velocity and RPM.... OR you can use a barrel with a slower twist rate.... The events which cause this are very complex, and there are no calculations or equations that can predict this behaviour....

This phenomenon is not related to the "Static Stability" or "Gyroscopic Stability", and in fact is virtually the opposite problem.... A bullet that has insufficient static stability will wobble and eventually tumble.... That is caused by too SLOW a twist rate....

Bob

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PostPosted: Sun Aug 05, 2018 12:17 am 
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Joined: Fri Jul 27, 2018 10:34 pm
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Location: Bowmanville, Ontario
Great explanation.

I was considering slowing the gun down until I realized the accuracy was more scope related than instability.
Somewhere along the way I ordered the nitro piston to fit the Benjamin. It is either MUCH more powerful than the .122" main spring I had, or, my scope was loose. Further testing is needed, but I wanted to open the discussion, cause, well... That's how I learn.
The nitro piston seems (from the 20~ pellets I had time to shoot) seems better and worse all at the same time. If I cannot iron out the issues, I'll go back to the spring since I had just dialed it in to shoot the arse out of a mouse, I believe I had coined it...

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