Does the Rifle Move?

[Bill Norris]

Don't read too much into the actual groups at this point but check out the very clear sine wave pattern on the target. This is a 100 yard test target. I'm not posting it to show that the groups are perfect or not, but that the sine wave is very apparent.

Very good shooting at any rate.

 

[gunsandgunsmithing]

Exactly! The sine wave achieved by varying charge weights agrees with Long's optimum barrel time, whereas he only considers muzzle diameter swell. Kolbe's results also exhibit phase shift dominates frequency using a tuner. I need to write up my method to determine the barrel vibration frequency from a charge weight ladder.

I'm not sure knowing the actual frequency "number" matters very much but using a tuner effectively is really as simple as quantifying on target, the value of each movement or graduation on the tuner relative to how far it is from completely in tune to completely out of tune along with reading the shape of the groups with each graduation. This target isn't as "classic" as I like to see in terms of reading the group shapes but it's clear enough that a pattern can be determined.

 

[gunsandgunsmithing]

Don't read too much into the actual groups at this point but check out the very clear sine wave pattern on the target. This is a 100 yard test target. I'm not posting it to show that the groups are perfect or not, but that the sine wave is very apparent.

Very good shooting at any rate.

Actually, I think the load might need a small tweak or possibly the best setting on that day may've been between the full number graduations used in this test. FWIW, I didn't shoot that target but it's a great example of the sine wave and groups changing size and shape. It also dispels the often stated idea that tuners only affect vertical. That statement is simply false.

 

[Straightshooter1]

Straightshooter1 -
I had the same idea to freeze the frames of the video, but came up with different images. Did you use the same video as the OP posted? Just curious.
Here are my freeze-frames:
View attachment 1326925

Thanks!
Alex

No, it's not the same video as the OP. But it is its twin that was also posted at the same time on YouTube but from a different caliber. I used it because I felt it was a better visual for the amount of the recoil movement:

 

[Alexander-M]

No, it's not the same video as the OP. But it is its twin that was also posted at the same time on YouTube but from a different caliber. I used it because I felt it was a better visual for the amount of the recoil movement:

Thanks!
Alex

 

[Dave M.]

I think his theory only represents one aspect of barrel movement. A common thing using his calculations is that most say they get you "close." Using a tuner, it's very clear that there are multiple sweet spots and they are relatively "close" together also. What I'm trying to say is that tune just repeats over and over again. The distance is based on the natural frequency of the barrel. With a tuner, we are slightly manipulating the frequency but more accurately, we are altering phase time. Essentially, this just means that we are shifting the top of the sine wave left or right to coincide with bullet exit. I'll post a pic in a minute. Don't read too much into the actual groups at this point but check out the very clear sine wave pattern on the target. This is a 100 yard test target. I'm not posting it to show that the groups are perfect or not, but that the sine wave is very apparent.

View attachment 1326946

The barrel makes Over 150 of these tiny sine waves as the bullet is traveling down the tube.
dave

 

[gunsandgunsmithing]

The barrel makes Over 150 of these tiny sine waves as the bullet is traveling down the tube.
dave

I think barrel stiffness has a role in that but it's a bunch, for sure.

 

[Dave M.]

I think barrel stiffness has a role in that but it's a bunch, for sure.

Barrel stiffness will affect amplitude, not frequency. Frequency is dictated by the speed of sound in steel.

 

[gunsandgunsmithing]

Barrel stiffness will affect amplitude, not frequency. Frequency is dictated by the speed of sound in steel.

There are multiple frequencies occurring at the same time and not just longitudinally. We can agree to disagree but I've measured significant differences in barrels with different stiffness values as well as with and without the tuner. Beyond that, the vibration analysis testing even showed frequency changes by un-gluing a glued and screwed pillar bedded action, and screwing it back into the existing bedding. So yes, frequency does change, not only with barrel stiffness but other factors as well, even beyond the barrel itself. Every joint in the system moves at high enough frequencies and those movements affect frequencies at the muzzle.

 

[6MMsteve]

Did the barrel actually move forward a bit, before it started moving backward?

The backward movement does not appear to be shooter induced, it looks smooth, but then again it is high speed in very slow motion, and in a rest.

But the small forward movement, if I’m actually seeing that right, I wouldn’t expect to see from recoil. I only watched the one short clip muted, so if the shot was narrated and didn’t involve a shoulder, I’m not aware.

barrel did move forward may a 1/16 or so, wouldn't that be the firing pin strike, I have no clue just wondering

 

[6MMsteve]

looks like the muzzle blast affected the tape measure and dow rod,

 

[davidjoe]

barrel did move forward may a 1/16 or so, wouldn't that be the firing pin strike, I have no clue just wondering

Not troll for a physicist, because they didn’t chime in last year, but If it’s shooter induced movement, (such as anticipating recoil or pulling back the trigger and gun with the hand, in either direction), the video, though well-recorded, wouldn’t apply more broadly, to all rifles.

If the gun moves rearward slightly in response to a column of air being accelerated to 3k FPS and forced out of it in front of the bullet, it (movement) would apply to all matches we shoot, etc.

If it moves back because part of the “whole”of “it” has moved forward, like a pendulum would do to a grandfather clock on a frictionless platform (slight side to side movement of the whole thing) then it’s not technically “recoil” in our common understanding, as it would get to the same place no matter how slowly the bullet reached the front.

Or, it is rearward, true recoil proportional to the energy of the bullet going forward, but there are some more difficult follow on questions that go with that.

 

[lb-ft]

I think a clear way to understand is if you took two rifles identical except one has a brake, and shot a video of both like that posted above, both behave identically up until the moment the bullet escapes the rifle and the rocket effect portion of recoil (all the gasses escaping the barrel) is introduced. The brakes rifle will recoil much less violently than the unbraked rifle.

 

[gunsandgunsmithing]

I think a clear way to understand is if you took two rifles identical except one has a brake, and shot a video of both like that posted above, both behave identically up until the moment the bullet escapes the rifle and the rocket effect portion of recoil (all the gasses escaping the barrel) is introduced. The brakes rifle will recoil much less violently than the unbraked rifle.

The "rocket effect" is minimal but it does exist. The primary affect of a brake is that it literally pulls the gun forward when the high pressure gasses and ejecta hit the sails of the brake.

 

[Dave M.]

There are multiple frequencies occurring at the same time and not just longitudinally. We can agree to disagree but I've measured significant differences in barrels with different stiffness values as well as with and without the tuner. Beyond that, the vibration analysis testing even showed frequency changes by un-gluing a glued and screwed pillar bedded action, and screwing it back into the existing bedding. So yes, frequency does change, not only with barrel stiffness but other factors as well, even beyond the barrel itself. Every joint in the system moves at high enough frequencies and those movements affect frequencies at the muzzle.

I don’t disagree with anything you just said Mike, all I stated earlier is the speed of sound in stainless steel (ie the frequency with which those vibrations take place) is unchanged. That’s just pure basic physics.

 

[Deleted Dewey]

Like most Youtube "technical" videos, I don't see what it is trying to prove. Julian Hatcher long ago proved what anybody who paid even minimal attention in high school physics knows: The rifle begins moving before the bullet leaves the barrel. I'm sure that there will be someone who "disagrees" but there are also people who think that the Earth is flat because it appears that way at ground level.

The internet, sadly, is often a soapbox for insecure people to shout: "Hey look, I know stuff!", usually because they "researched" it on Google.

 

[Dave M.]

I don’t disagree with anything you just said Mike, all I stated earlier is the speed of sound in stainless steel (ie the frequency with which those vibrations take place) is unchanged. That’s just pure basic physics.

Not to mention Mike, you are the guru that understands rifle turners perhaps better than anyone on this forum. Thanks.
Dave

 

[CA_Shooter]

I think his theory only represents one aspect of barrel movement. A common thing using his calculations is that most say they get you "close." Using a tuner, it's very clear that there are multiple sweet spots and they are relatively "close" together also. What I'm trying to say is that tune just repeats over and over again. The distance is based on the natural frequency of the barrel. With a tuner, we are slightly manipulating the frequency but more accurately, we are altering phase time. Essentially, this just means that we are shifting the top of the sine wave left or right to coincide with bullet exit. I'll post a pic in a minute. Don't read too much into the actual groups at this point but check out the very clear sine wave pattern on the target. This is a 100 yard test target. I'm not posting it to show that the groups are perfect or not, but that the sine wave is very apparent.

View attachment 1326946

Are groups 6 and 7 really due to wind or could that also be due to barrel oscillation?

 

[!Peter!]

Be interested to know how the rifle/ action was held. Looks like its in a free recoil arrangement something like a rail gun.

 

[gunsandgunsmithing]

Are groups 6 and 7 really due to wind or could that also be due to barrel oscillation?

I can't answer that, as I said, I didn't shoot that target.