Sine waves

[Link]

What causes signwaves? Is it bolt lugs? Yes I did a search. ;}

ty Don.

 

[Tommie]

Search for sine waves. Might have better luck.

 

[GunzRUs]

What causes signwaves? Is it bolt lugs? Yes I did a search. ;}

ty Don.

I went to a class a while back that covered sine wave. It's a vibration caused by the bullet traveling down the barrel (referred to as 9th sine) I believe, it's been a while so could be wrong.

 

[JMayo]

I would think it's a big ass explosion in the chamber that causes sine waves.

 

[Beiruty]

Are you referring to the POI shift vs powder charge?

 

[JFrank]

I believe he is referring to the carbon/ soot line along the case neck OD after ignition which seems to exclude the lug area.

 

[joshb]

Think “shock wave”.

 

[Link]

Are you referring to the POI shift vs powder charge?

powder charge. Waves on the neck.

 

[Kracken McGraw]

Proper neck clearance.

 

[jackieschmidt]

Proper neck clearance.

Like this.

 

[Dave M.]

Like this.View attachment 1345752

Jackie what are you running for neck clearance from brass to chamber? That is a beautiful pattern on the neck. Textbook. Looks just like the drawing in Tony Boyer’s book. Is that from a single firing? I imagine so, because you could never get the brass to index you the same position multiple times.
Dave

 

[Beiruty]

Using the slow powder to push a heavy bullet, the burning is so slow, that the case neck does not seal the chamber and carbon would seep back between the case and the chamber wall leaving those black marks.

 

[perry42]

The ignition of the powder charge and the engagement of the bullet in the lands & grooves cause the barrel to vibrate. When shootng black powder silhouette I discovered the practice of lightly dusting the barrels of my BPCR rifles then holding them barrel down by the stock and striking the bottom of the barrel with a rubber mallet. When done correctly you will see a sine wave in the powder. I would always place the rifle in the crossed sticks just forward of the fore stock where the sine wave is at zero. ( Either coming up or down )
My Browning BPCR's always shot the best using this little trick.
perry42

 

[Dusty Stevens]

Jackie what are you running for neck clearance from brass to chamber? That is a beautiful pattern on the neck. Textbook. Looks just like the drawing in Tony Boyer’s book. Is that from a single firing? I imagine so, because you could never get the brass to index you the same position multiple times.
Dave

I get it with .0015 and i get 3 waves on a 3L action

 

[1911nut]

So we don’t know what causes the sign waves?

 

[Dusty Stevens]

So we don’t know what causes the sign waves?

Lugs on the bolt

 

[Dusty Stevens]

 

[JMayo]

Oh i get it now. Strange to me terminology.
my 30 is wavy & close to the case mouth.
My 6ppc is about half the neck.
My 6bra is right at the neck sholder junction .. old hard brass it even goes to half the sholder.

This difference tells me it's about head space & case expansion speed.
Too much energy spent expanding case body allows the gases get around more.

I suppose a 3L holds the case more square and the line would be less wavy.. idk ... interesting though.

 

[deadidarren]

This the neck on my 260R after 16 loadings .

 

[rijndael]

When shootng black powder silhouette I discovered the practice of lightly dusting the barrels of my BPCR rifles then holding them barrel down by the stock and striking the bottom of the barrel with a rubber mallet. When done correctly you will see a sine wave in the powder. I would always place the rifle in the crossed sticks just forward of the fore stock where the sine wave is at zero. ( Either coming up or down )

How do you know the frequency of the sine wave, which determines the 'zero', is the same when fired vs when hit with a mallet?