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Old April 16, 2018, 10:02   #1
JohnnyJohnsoninWI
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What is the amplitude of barrel vibration?

Or, how much gap does a free floated barrel really need in order to truly be free-floated? Obviously, we are discussing bolt guns here.
I've been thinking that the old "dollar bill" test probably isn't enough gap to prevent the barrel from touching the forearm when shooting. I've also been thinking that the barrel likely has two sources of vibration; the first being launching the bullet and the second being a whip action caused by recoil. I also suspect the latter is the larger.

Is there some kind of pressure sensitive paper that changes color when pressure is applied? I feel another experiment in the works.
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Old April 16, 2018, 11:19   #2
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what is the frequency, kenneth?
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Old April 16, 2018, 11:23   #3
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Quote:
Originally Posted by JohnnyJohnsoninWI View Post

Is there some kind of pressure sensitive paper that changes color when pressure is applied? I feel another experiment in the works.
Strain gauges.....

YMMV
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Old April 16, 2018, 11:53   #4
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Quote:
Originally Posted by JohnnyJohnsoninWI View Post
.. . .
Is there some kind of pressure sensitive paper that changes color when pressure is applied? I feel another experiment in the works.
I purchased some years ago for work. Not sure if they have something that responds quickly for a transient load, but worth asking. No idea about price, either.
I still get e-mails from this fella:

Vadim Shalyt
Sr. Application Specialist
Sensor Products Inc. USA
300 Madison Ave.
Madison, NJ 07940
1.973.428.8985 (Office Phone)
1.973.495.9800 (Cell / Text / WhatsApp)
vshalyt@sensorprod.com

There is also high-speed video. Probably hard to extract precise displacements, but movement will most likely surprise you.
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Old April 16, 2018, 12:19   #5
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re: strain gauges

I don't need strain gauge the level of technical depth I'm digging into. I just want to know if the barrel touches any part of the forearm when shooting. If it does, and it doesn't matter how hard it's touching, it isn't really free floating.

I've seen rifles with 1/8 gap between the stock and barrel. No doubt, that sucker is free floating, but it seemed a bit overkill. On the other hand, I think a paper shim thickness gap probably isn't enough to ensure the barrel isn't touching the stock every time in all shooting positions.
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Old April 16, 2018, 13:20   #6
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Compression wave amplitude will be dependent upon a multitude of variables for any given barrel/receiver/stock combination. Some intrinsic, some applied force, others environmental. No easy answer, and an answer in flux.

Best you could probably do is to test for a maximum, then oversize your gap by another 10% or so.
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Old April 16, 2018, 13:26   #7
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Quote:
Originally Posted by JohnnyJohnsoninWI View Post
I don't need strain gauge the level of technical depth I'm digging into. I just want to know if the barrel touches any part of the forearm when shooting. If it does, and it doesn't matter how hard it's touching, it isn't really free floating.

I've seen rifles with 1/8 gap between the stock and barrel. No doubt, that sucker is free floating, but it seemed a bit overkill. On the other hand, I think a paper shim thickness gap probably isn't enough to ensure the barrel isn't touching the stock every time in all shooting positions.
Carbon paper....

YMMV
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Old April 16, 2018, 13:31   #8
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- carbon paper

I was thinking of that. It's a cheap try.
Agree with Tuhlmann, test for a maximum and oversize by 10%.
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Old April 16, 2018, 13:33   #9
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Silly putty?
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Old April 16, 2018, 13:38   #10
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Plasti-gauge ?
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Old April 16, 2018, 13:40   #11
JohnnyJohnsoninWI
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carbon paper

The more I think about it, the more I'm liking the idea of carbon paper with a cigarette paper backer. Together, they're quite thin, maybe .005, yet they'd leave a witness mark on the cigarette paper if there was any impact or rubbing during shooting. Interesting to find out. Thanks.
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