The Purdy Prescription

The thread you linked to doesn't show much except a number of testimonials (which are fine) and refinements on the basic formula, whatever that is. All welcome, but what's the original prescription?

Google search for "Purdy prescription" shows the site you've linked to, and the two on BR Central.

Post 11 on the RA site did have a formula, but it wasn't well formed for in-line math. e.g.

(BL/8 x 9) - 0.45" = PL
PL - BL = Tuner Length

is not well formed. Is it suppose to be

[(BL/8) x 9] - 0.45 = PL.
PL - BL = Tuner Length

or

[BL / (8x9)] -.045 = PL
PL - BL = Tuner Length

? I'd assume the first, (since in the 2nd, "(8x9)" could be simply expressed as "72", but we got one guy presenting another's work, so who knows...)

And what the blazes is H/H?

Given the man in inundated, is there somewhere where we can just go & see his prescription without bothering him?

TIA

Hi Charles

Just drop me an e-mail and I will be glad to send you my worksheet. prx2500@outlook.com

H/H stands for Harrels/Hoen Tuner.

Have a good day

Tony
 
To All:

What may or may not have happened on WWA is really nobody's business except mine. And I will not comment on it. I ask you all to do the same.

Tony

I wont make any comments except to correct false accusations and the mere fact that your posts are currently up and readable are proof enough that the fellow I corrected needed correcting. Anything that happened privately should stay private.
 
Tony

I worked your formula for my von-ahrens tuner and at present am trying to figure out how to lengthen it to accommodate the results.I wonder if I can just cut the bloop tube to the correct length for the length.of the tuner or does it need the weight of the lengthened body? IF this is trully harmonics then weight shouldnt come in to play should it?
 
I worked your formula for my von-ahrens tuner and at present am trying to figure out how to lengthen it to accommodate the results.I wonder if I can just cut the bloop tube to the correct length for the length.of the tuner or does it need the weight of the lengthened body? IF this is trully harmonics then weight shouldnt come in to play should it?

Hi Mike

I appreciate you sharing about your VA tuner. I may not have sent you the pic of the tuner sent to me by my friend in the UK. He cut off the bloop tube extension to allow him to shorten the length to meet his requirements on his barrel. It apparently is now a shooter and with the lightened weight qualifies for both HV and LV classes.

In all the calculations I have done, I have never considered weight as part of the equation. Barrel length and opening diameter of the tuner are the only considerations in my formula

With the VA weights, you may end up being quite a bit heavier if you go for a longer length. As long as you have done the numbers correctly and get to the length prescribed by that, your barrel should be in tune

Have a great nite

Tony
 
Tony

Hi Mike

I appreciate you sharing about your VA tuner. I may not have sent you the pic of the tuner sent to me by my friend in the UK. He cut off the bloop tube extension to allow him to shorten the length to meet his requirements on his barrel. It apparently is now a shooter and with the lightened weight qualifies for both HV and LV classes.

In all the calculations I have done, I have never considered weight as part of the equation. Barrel length and opening diameter of the tuner are the only considerations in my formula

With the VA weights, you may end up being quite a bit heavier if you go for a longer length. As long as you have done the numbers correctly and get to the length prescribed by that, your barrel should be in tune

Have a great nite

Tony

Does the body of the tuner need to be at the prescribed length or can I just cut the bloop tube to the prescribed length?
 
Tony

After thinking about your RX wouldn't it be possible to fabricate a tube to be attached to the muzzle that is just a straight tube the diameter of the barrel and using your formula make it to the proper length and (if this is truly a harmonic tune) without all the extra weight it should be in tune shouldn't it?Now if it isn't then that will tell me this formula is just a coincidence to figure the proper WEIGHT that needs to be on the tuner, i.e. that making the body the proper length also coincides with the proper weight.This is really a fascinating thing and has my interest piqued, I cant wait to get to the range and test this.I have made up a harrels tuner to the proper length and am going to try that, I have made a VA tuner with the bloop tube to the proper length and am in the process of making a weight(aluminum) to make the VA body the proper length, if they all fall into tune then we will know for a fact it is a harmonic tune, if they don't then we will know it is a combination of harmonic and mechanical tune.I have always thought that harmonics play a part I just don't know how much.

Mike Cameron
 
Good Morning Mike

I apologize for not answering sooner. A couple of very experienced shooters have tried several different combinations of lightened tuner shells, inner tube extensions, etc and the results have pretty well mirrored expectations.

I am not saying that length is the only factor. Otherwise a rolled up piece of paper would work:p.

By all means, test this process to its limits. The worst that can happens is it fails.

I have to head to work now, so I'll check back this evening

Have a great day my friend

Tony
 
After thinking about your RX wouldn't it be possible to fabricate a tube to be attached to the muzzle that is just a straight tube the diameter of the barrel and using your formula make it to the proper length and (if this is truly a harmonic tune) without all the extra weight it should be in tune shouldn't it?


That’s exactly what I did Mike (for an air rifle, but the principal is the same):

tuner_zps0b84abc1.jpg




The barrel is 16mm and the OD of the sleeve is 23mm (just because it looked right).

Hopefully get chance to try it later today, certainly by the weekend.

Brian
 
Hi All

That is one sharp tube, Brian. When I get some time this evening I will post the pic of mine.

When I originally started talking about this about a year ago, I was adamant that all you had to do was do the math, cut a tube with enough length to attach it to the barrel, and it would be in tune.

The tuner on "Wind Chime" is really nothing more than a stainless steel tube 1.25"OD X .75"ID bored 1" back the diameter of my barrel for attachment. I have two tuners for my Kimber, both made to almost the exact same dimensions. One is stainless the other is aluminum. The only difference between the two when I shoot them, is that the POI changes by about .060. Grouping stays consistent

Mike,, if I understand you correctly you are asking if a tube, say the size of the tube on your VA, was cut to the desired length, would that tune the barrel. In the testing that a couple of my friends have tried, the short answer is YES!!

Hopefully, here in the near future, I will have additional information I can share.

Feeling a bit under the weather today, so I I'm off for a nap

Thanks

Tony
 
Hint to Measure Barrel

I decided to check my tuner setting using Tony's formula.
End result I had to go out 200 clicks. :(

To measure the Barrel length I slipped a "Sipper Straw" over my cleaning rod and then slid it down until it bottomed on the crown.
The Ridges at the one end held it snugly in place so I could pull out the rod & measure fairly accurately.
(Big Advantage was I did not have to remove the Tuner!)
Next I plugged the BL into my spread sheet to get the overall length -PL.
Slid the straw out to the PL, bottomed out my cleaning rod and adjusted my tuner to the new PL length. (Straw end flush with end of Tuner)
 
I did my Turbo today

I had to move the tuner out more than half an inch to get to where the formula said tune was to be. I had been shooting the rifle with the tuner even shorter than it is with the spacer. Tony recommended setting the tuner @ about half of it's range, which I did with the move.. It come right into tune nicely in 4 clicks. Amazing, me thinks.

Pete
 
I had to move the tuner out more than half an inch to get to where the formula said tune was to be. I had been shooting the rifle with the tuner even shorter than it is with the spacer. Tony recommended setting the tuner @ about half of it's range, which I did with the move.. It come right into tune nicely in 4 clicks. Amazing, me thinks.

Pete

Hi Peter

Big thumbs up!!!! I love it when a plan comes together.

Glad it is working out for you

Tony
 
Doug
Who's spreadsheet?

Hi Fred

Several shooters have gone the extra mile and started putting the formula into a spread sheet where all they have to do is put in the barrel length and they get the answer.

I am more of a stubby pencil kind of guy, .

I have been given a spread sheet that I am currently going over for accuracy and a few personal tweaks before I roll it out.

Tony
 
Making my own

I've be experimenting with a spreadsheet of my own. I want to see as many variable as I can within reason. Compute and then test. Problem is, I only get to test during matches every two week. Sat is coming up so I can try several more configurations. Which harmonic is best, will only be determined at the target. I'm finding several different combinations that look very good. Time will tell. Programing is a B****.
 
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Re Re-did the Turbo

After making the spacer for the tuner I decided to re-measure the Physical length. Sure enough, I somehow miscalculated on the spacer so I re-set the tuner. I was going back to the garage to do more air rifle testing so shot the Turbo. The new setting-distance proved to be an excellent position. I have read in the past that when one finds tune, a click or two on way or the other won't matter much. It seems to be so with this setting. I was able to shoot some tiny round holes two clicks either side of 274 but 274 was repeatedly tiny round. I have been shooting that rifle for two years and never really in tune in spite of how well it has shot at times. Tune appears to be nearly two inches beyond where I have been shooting it.

Pete
 
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