The Purdy Prescription

Tony

I am sorry to report that the simple tube(pure harmonics) just doesnt work. I had my VA tuner with the bloop tube cut to length and put it on and it shot several rounds in a very small group but then started throwing high and low. I took the VA off and put my harrels tuner on set to the proper length and it worked perfectly, this tells me that you have to have the weight of the barrel set to the proper length.I am in the process of making an aluminum weight for the VA at the proper length and if it performs right then I will be completely sure that it requires the weight to make tune.I do believe that harmonics is a part of this but am almost convinced that mechanical weight is necessary. Has anyone just made a tube with and attachment device? If so did it work for more than a few. Shots? Myself and B. Collins did a good bit of testing yesterday and had a real blast with this theory, it is very encouraging to say the least, and if it saves people ammo (AND IT WILL) it will be very usefull.
Mike Cameron <-------my real name
 
Hi Mike

I appreciate you running that test. I am puzzled at why it would work at first, and then start to throw flyers. Brian K said the same thing with his air rifle. Very Curious. Patterns are great for showing direction of thot.

My tuner is a one piece tube, but it is not a true class A benchrest rifle. My results don't count.

Was the Harrel tuners set to your tune, or a PRX tune?

I do want to learn from the tests that don't work out. Could you send me a PM or an email with the particulars of the tube and barrel? Or we could talk about it here. Your choice.

Thanks Again

Tony
 
PakRat said:
Hi Mike

I appreciate you running that test. I am puzzled at why it would work at first, and then start to throw flyers. Brian K said the same thing with his air rifle. Very Curious. Patterns are great for showing direction of thot.

My tuner is a one piece tube, but it is not a true class A benchrest rifle. My results don't count.

Was the Harrel tuners set to your tune, or a PRX tune?

I do want to learn from the tests that don't work out. Could you send me a PM or an email with the particulars of the tube and barrel? Or we could talk about it here. Your choice.

Thanks Again

Tony
Click to expand...

The harrels tuner was set to the PRX length as the formula prescribed.
I went back and checked my sporter(there is absolutely no doubt that it is tuned) and according to the RX the dogknot shoud be .500 longer than it is Now figuring with the 9th harmonic I went back and just for kicks punched in the formula with the 11th harmonic and it came out exactly where the dogknot is. It could be we still aren't in the right harmonic with the formula and I am planning on working out each harmonic 11th, 13th, 15th and seeing how each one tunes maybe we will hit one that is even better than the 9th.

Mike Cameron
 
Hi Mike

Great job running the numbers for the different harmonics. I have another shooter that came to the same conclusion. There may be some barrels that respond better to different harmonics than others.

The more different combinations that are tried, the better the results get, and I am able to tweak the formula if needed.

The flow of information is starting to come back and I am looking forward to matching prediction to results.

You have been a great help, Mike, and I appreciate it greatly.

Tony
 
MIKECAMERON said:
I am sorry to report that the simple tube(pure harmonics) just doesnt work. I had my VA tuner with the bloop tube cut to length and put it on and it shot several rounds in a very small group but then started throwing high and low. I took the VA off and put my harrels tuner on set to the proper length and it worked perfectly, this tells me that you have to have the weight of the barrel set to the proper length.I am in the process of making an aluminum weight for the VA at the proper length and if it performs right then I will be completely sure that it requires the weight to make tune.I do believe that harmonics is a part of this but am almost convinced that mechanical weight is necessary.
Click to expand...

I believe you're right. I know it has the Centerfire stigma attached, but see Vaughn's Rifle Accuracy Facts, page 81. The curve shown for the improvement by adding weight flattens out, indicating (as Vaughn says) that some weight is beneficial, but after 3.2 ounces adding weight gets you a lot less effect per ounce, and after 5.5 ounces, less still.

One admittedly expensive test would be to counterbore a reverse taper barrel, and see if counterboring a computed amount would itself be enough. Or, more to the point, a Sporter profile barrel. Shouldn't be too hard to compute the depth and the width of the hole needed via the counterboring...
 
Last edited:
MIKECAMERON said:
The harrels tuner was set to the PRX length as the formula prescribed.
I went back and checked my sporter(there is absolutely no doubt that it is tuned) and according to the RX the dogknot shoud be .500 longer than it is Now figuring with the 9th harmonic I went back and just for kicks punched in the formula with the 11th harmonic and it came out exactly where the dogknot is. It could be we still aren't in the right harmonic with the formula and I am planning on working out each harmonic 11th, 13th, 15th and seeing how each one tunes maybe we will hit one that is even better than the 9th.

Mike Cameron
Click to expand...

Hi Mike

This may be a dumb question, but is the barrel on your sporter counter bored? I am way too tired right now, so bear with me.

Thanks
Tony
 
Ahuuuuum!

Charles E said:
I believe you're right. I know it has the Centerfire stigma attached, but see Vaughn's Rifle Accuracy Facts, page 81. The curve shown for the improvment by adding weight flattens out, indicating (as Vaughn says) that some weight is beneficial, but after 3.2 ounces adding weight gets you a lot less effect per ounce, and after 5.5 ounces, less still.

One admittedly expensive test would be to backbore a reverse taper barrel, and see if backboring a computed amount would itself be enough. Or, more to the point, a Sporter profile barrel. Shouldn't be too hard to compute the depth and the width of the hole needed via the backboring...
Click to expand...

Mr Charles E,

Didn't you take me to task for using the term "backboring" incorrectly in this instandce, instead of counterboring, not long ago? :)

Pete
 
PakRat said:
Hi Mike

This may be a dumb question, but is the barrel on your sporter counter bored? I am way too tired right now, so bear with me.

Thanks
Tony
Click to expand...

Yes it is Tony and the depth works out to the 11 harmonic finding, I guess I wasn't specific enough to draw a clear picture, my bad.

Mike Cameron
 
Hi Mike

I was pretty sure I already knew, but I had to ask anyway. Sometimes its easier to just ask the question than it is to assume I know the answer.

I appreciate your patience with me

Tony
 
You must log in or register to reply here.
Back
Top