PRX Formula help me understand it a bit......

CYanchycki

CYanchycki

Club Coordinator
Well folks, April in Manitoba, and winter decided to give us one more blast of snow. I am a Short Range Bench Rest shooter (6PPC) but decided I should play around with my Feinwerkbau with a H/H Tuner. Short Range BR is frustrating but I find RimFire even more so. Snowing out so I decided I should play around with this PRX Formula stuff and see if I can figure it out.

I hope I understand the calculation process so this is what I have come up with.

Barrel length is (26.375"/8)X9-.2805EC=29.391" Thus 29.391 would be my overall length .

To achieve that length I have the shortest weight length on the end of the tuner. I thus had to use the EC as calculated below.

I came to the EC of .2805 in this manner. The hole of a weight ring for my Harrel tuner is .935"x.3=.2805. Is this the correct mannner in calculating EC?

If I did not use a weight on the end the EC would be .1875. Hole of tube .625X.3=.1875 I figured I may not have enough adjustment if I did not use the weight ring to achieve the desired length so thus the EC of .2805 was used.

Is this correct? If so this calculation process makes sense to me, if not.......... AUGH

Another question, I have read about guys tuning to the 5th or 7th node. How do they know what Node? Does this have to deal with the Divide by 8 number or Multiply by 9 number in the calculation? Does one of those numbers in the formula represent the node you want to try and strive for to reach the desired barrel length?

It appears from the little I have read (not much of a reader) tuner weight is not the issue it is the length that matters?????? Is this correct?

Does velocity of the bullet used not play a factor?

Does this make sense what I am trying to convey??????

Calvin
 
Lots of questions..I can answer a couple.
The ec formula that you are using sounds right. Tony has said that if the id is less than .250 DEEP to use the smaller id. In other words, if the weight is .250 or more thick, to use it's diameter instead of the inner part of the tuner itself. I feel there may be a small amount of room to fudge this, to suit your particular rifle...a few clicks one way or the other.. JMO.

And yes, the harmonic to which you are tuned is the multiplier, but the quarter wave length is the harmonic minus 1. So to tune to the 9th harmonic, you divide the barrel length by 8 and multiply the answer by 9 to get the acoustic length.

If tuning to the 11th, for example, divide the barrel length by 10 then multiply that by 11.

It's really amazing that this works, and maybe more so that Tony figured it out so that we can find a good tune without wasting that precious ammo.
Almost everyone that I talk to agrees that it works on their gun. IME, I can't shoot better than this tune gives me. I'd be hard pressed to say for sure that any other spot on my tuner is any better.

Simply amazing!
 
Hi All

Thanks Mike for jumping in. My computer has crashed, so I am kind of at a panic stage right now. Using my wifes laptop right now and it is soooooo slow.

What part of this means for you Calvin, is that I am going to have to work to download files off my computer so I can send you the worksheet

Mike, thanks again for your support of PRX.

Calvin, you basically know everything you need to know to make PRX work for you. If you use a weight ring to increase the length, be sure to you use the EC based on that opening. I got your email Calvin and will send you the worksheet as soon as I can. I helps explain some of the other tunes
 
Tony..just trying to be of help. Set me straight if I need to be on anything that I said.

Calvin...as to speed and tuner weight...The PRX, IMO, brings into question more traditional ways of tuning. Not that we can't get to the same point, but what we are actually accomplishing with weight may be different than many have been trying to gain from it, in reality.

Working with my new PDT tuner, I have become convinced that we were gaining a wider tune window by adding weight..to a large degree, but with a point of diminishing returns somewhere, dependent on factors such as barrel contour, and possibly velocity variations that may go beyond what we can tune out with weight alone. Nevertheless, a wider window will make finding a good tune easier.

This line of thought is in part why I began searching for a more efficient way of dampening barrels. Testing my tuners, I conclude that particle dampening seems to give even more control of vibration than just weight on the end of a barrel, but you can't just add two or three tiny specs of tungsten and achieve much of anything....we still need weight, just not as much of it if part of that weight is "active", aiding in dampening.

It's all very interesting.
 
Thanks

guys. Not being a Mathematician or spelling teacher......LOL........ it feels good to know that I can figure out some simple formula calculations.

It is pretty simple when you know the components to the equation and how the different input values are derived. Now to test this out on the Feinwerkbau and to get another tuner for my CZ 452 with a Benchmark reverse taper.

So HOW in the HELL did you ever come up with the Formula????? LOL

Calvin
 
From what I am seeing with my new rifle,

Weight definitely seems to be a factor. While I can find a tune using PRX, I find I need to have the Harrell's bell out to 500 to have a better tune. To that end, I bought a 1.8 oz. weight to try. I am thinking I am close to something real good.

I tried using a von Ahrens on this rifle and with all the weights I have for it, I was just able to get it into tune with the "Moderator Ring" screwed in as far as it would go. I think this is telling me MORE WEIGHT but could be wrong. This is with the bloop tube in the von Ahrens set on the PRX number.

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