PPC nodes

[kolar55]

I'm fairly new to the 6ppc. I have read that the charge weight nodes are approximately 1.2gn, apart. Meaning that something between that would be "out of tune".? I recently read something that stated nodes in general were 3% apart. That would be .8 to .9 gn apart. Can anybody here shed some light on this?
Thanks Lonnie

 

[Andy Cross]

Nodes

Many years ago I set about testing where the nodes for a barrel actually fell. It was done by firing a rifle with its barrel within the core of an electromagnet. It floated within the field and didn't touch anything. The vibration pattern cut through the lines of force inducing a voltage. I won't go into the nitty gritty but you can join the dots. The primary signal and the secondary flyback signal were displayed on an oscilloscope. Some of the things that altered where the nodes fell were the length of the barrel, profile and overall weight. The only way to know where they will occur is to load test. Can't see any other way around it.
Andy.

 

[JerrySharrett]

The late great rimfire gunsmith and shooter Bill Myers once set up some electronic indicators that would hold the extreme readings. One of the interesting things he found out was that the barrels primary vibration pattern was from 7:00 to 1:00, not 6:00 to 12:00 as we would imagine.

Consider too, a steel barrel is not unlike a steel musical instrument string. Its vibration in amount, frequency, and direction is dependent upon the items length, diameter and physical strength. This half number (click) of 0.3 grains comes from what has ben used for years, the Culver type measure. So, for while it might seem the barrel magically fits into this 0.3 g, 0.6g, etc relationship from node to node may not be linear at all, i.e., it may be logarithmic, or ????




,

 

[B.Larson]

Nodes

Many years ago I set about testing where the nodes for a barrel actually fell. It was done by firing a rifle with its barrel within the core of an electromagnet. It floated within the field and didn't touch anything. The vibration pattern cut through the lines of force inducing a voltage. I won't go into the nitty gritty but you can join the dots. The primary signal and the secondary flyback signal were displayed on an oscilloscope. Some of the things that altered where the nodes fell were the length of the barrel, profile and overall weight. The only way to know where they will occur is to load test. Can't see any other way around it.
Andy.

Thank You Andy... for trying to figure out nodes in a technical manner...... ..... GOOD WORK.... time well spent and with an answer..... it`s easier to actually test individual barrels.......
I am also of the opinion barrel length,material type,bore size are some things that affect nodes and will make data applicable to each individual barrel......
bill

 

[Wilbur]

I'm going to go out a creaky limb here and ask what I missed along the way? What is the problem with just trying a load out to see if it shoots...and not fooling around with trying to understand why or how or anything else.

It just takes two shots!

 

[Boyd Allen]

Some knowledge of node spacing can speed up tuning a bit. Testing is a good way to determine that spacing for a particular configuration. The comment that was originally made by Gene Beggs about node spacing of a 6PPC was for a typical short range rifle, and was based on his testing. It has come in handy on those occasions when I have needed to decide how much of a charge weight change to make. Perhaps some day I will try to figure out the spacing of seating depth nodes.

 

[kolar55]

Some knowledge of node spacing can speed up tuning a bit. Testing is a good way to determine that spacing for a particular configuration. The comment that was originally made by Gene Beggs about node spacing of a 6PPC was for a typical short range rifle, and was based on his testing. It has come in handy on those occasions when I have needed to decide how much of a charge weight change to make. Perhaps some day I will try to figure out the spacing of seating depth nodes.

That's pretty much what I was looking for. I have a typical short range 6PPC, and was was wondering what the spacing was that turned up most often.

 

[JerrySharrett]

I'm going to go out a creaky limb here and ask what I missed along the way?


It just takes two shots!

It's them wind boogers, I know it is!

.

 

[sofarfrome]

The late great rimfire gunsmith and shooter Bill Myers once set up some electronic indicators that would hold the extreme readings. One of the interesting things he found out was that the barrels primary vibration pattern was from 7:00 to 1:00, not 6:00 to 12:00 as we would imagine.

Consider too, a steel barrel is not unlike a steel musical instrument string. Its vibration in amount, frequency, and direction is dependent upon the items length, diameter and physical strength. This half number (click) of 0.3 grains comes from what has ben used for years, the Culver type measure. So, for while it might seem the barrel magically fits into this 0.3 g, 0.6g, etc relationship from node to node may not be linear at all, i.e., it may be logarithmic, or ????,

I wonder if it would be 5 to 11 if the twist of the barrel went in the other direction?

 

[Andy Cross]

A bit more info

Thank You Andy... for trying to figure out nodes in a technical manner...... ..... GOOD WORK.... time well spent and with an answer..... it`s easier to actually test individual barrels.......
I am also of the opinion barrel length,material type,bore size are some things that affect nodes and will make data applicable to each individual barrel......
bill

The whole idea behind the work I did was to figure out some of the things that made a barrel not shoot. We found that when the secondary or fly back signal heterodyned with the primary the bullets exited the muzzle all over the place. Just small velocity variations caused displacement on the target greater than they theoretically should have. 4 barrels were chosen that the shooters had relegated to fire forming duties because they wouldn’t shoot.

We found the secondary heterodyned with the primary in every case. One barrel had a saw tooth on the crest of most waves which indicated movement at the anchor point. With the barrel correctly torqued up the chamber was pushed 20 thou further along the barrel. This almost had the two waves counter heterodyned. The muzzle was then re-crowned 5 thou and the two waves were counter heterodyned quite well.

The first group was a .162 at 100 yds. The best group prior to the work was .335 The other barrels were given the same treatment. Then they took ‘em to the nationals the next year and did quite well with them. The moral of the story is that just about any top quality barrel probably has hummer potential. It’s just a matter of extracting it.

The issues with this sort of a tune up is that the shooter would need to have the smith and his workshop handy and close to a range. Would need access to someone who could operate the test equipment and make the correct diagnosis and be able to tell the smith what to do. Impractical for most of us. But if you had deep enough pockets it is doable.


Jerry also mentioned a steel barrel is not unlike a steel musical instrument string. Its vibration in amount, frequency, and direction is dependent upon the items length, diameter and physical strength.

Quite true. With one important difference. Unlike a musical instrument the barrel isn’t anchored at both ends like most stringed instruments. That puts quite a different slant of the way it behaves. Just to complicate matters we have a moving plug made of copper and lead called a bullet moving along the string. With the number of intervening variables involved I think it’s a miracle we get the groups we do.
Andy.

 

[mks]

Andy,
What could you measure with this technique? Could you get horizontal and vertical position and/or muzzle angles? Or just vibration frequency? How well could you isolate the measurement to a particular point along the length of the barrel?

Thanks,
Keith

 

[Andy Cross]

Back in the day

Andy,
What could you measure with this technique? Could you get horizontal and vertical position and/or muzzle angles? Or just vibration frequency? How well could you isolate the measurement to a particular point along the length of the barrel?

Thanks,
Keith

Back in the day when I was doing this ie late '80s what you are asking would have been pretty difficult. I would have required the help from an electronics engineer as well. But with the filtering and isolation software available these days all of the above are doable.
Andy.