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View Full Version : Any new info on the PRX?



Pete Wass
12-01-2013, 04:32 PM
Some time has gone by now and I have been wondering if there have been any new findings for folks who are using the PRX.

Thanks,

Pete

Evelio
12-01-2013, 06:54 PM
Pete
I tried the PRX formula, and was two clicks off from what I consider a good tune, I also started adding weights to the tuner, and it pretty much stayed in tune, but the weird thing, is that the POI did not changed much. WEIRD this was tried on a 24 1/2" barrel.
I tried it on a 22 1/4" barrel and it did not work.
Evelio.

The Jet
12-01-2013, 07:04 PM
I recently purchased a new falcon ,shillen barrelled benchrest rifle in Australia. Which the smith a Australian champion shooter set the tuner on and test fired 5 shot groups of less than 0.3 inches at fifty metres in windy conditions. When I received rifle being a complete newby I photographed the turner setting and set about using Tonys system to test his tuning settings. Since we live in a country that uses millimetres instead of inches. I simply converted the end corrections into metric and removed the Harrel tuner . Took the barrel length to the closed bolt using the ninth Harmonic I calculated the harmonic length. Then subtracted the end correction which was the inside diameter of the tuner . Replaced tuner and wound it to physical length.

Result : Exactly the same setting on the tuner as the setting that my gun smith had set and test fired those great targets. Like exactly the same setting which astounded me.

Tonys system works and works well ,Enough said.

Kind regards Ben
ps however there is still a small issue with factory barrels 20 inches long like the Anshultz 2013 because I can not work out how to get the system to work with that shorter length . We all know that the Anshulz rifle is a fine shooting rifle.

Evelio
12-01-2013, 08:17 PM
I had the same problem, the PRX seams to work OK on barrels 24" & longer, I can't make it work on less than 23" long.
Evelio.

PakRat
12-01-2013, 08:38 PM
Hi All

This is a discussion I would like to see progress.

I am overwhelmed at how many shooters have had success with PRX, but true learning for me comes from the ones who have not had success.

I have not talked to much about the other harmonics, but the 9th is not the only one you can use. On shorter barrels, using a standard Harrels, you might try using the 7th harmonic. Same principle, just divide by 6 and multiply 7. You might need a weight ring depending on how long the barrel length is.

It would be neat if the Harrels tuner came in a version that was about .5" shorter and had no inner tube. This would be a boon for the shorter barrels.

I helped a shooter in the UK who had a short barrel. He had a custom tuner that when we ended up, was a short squatty little thing, but man, does that gun shoot.

Got to get up early tomorrow so I'm off to bed.

Have a great nite

Tony

Pete Wass
12-01-2013, 08:42 PM
I recently purchased a new falcon ,shillen barrelled benchrest rifle in Australia. Which the smith a Australian champion shooter set the tuner on and test fired 5 shot groups of less than 0.3 inches at fifty metres in windy conditions. When I received rifle being a complete newby I photographed the turner setting and set about using Tonys system to test his tuning settings. Since we live in a country that uses millimetres instead of inches. I simply converted the end corrections into metric and removed the Harrel tuner . Took the barrel length to the closed bolt using the ninth Harmonic I calculated the harmonic length. Then subtracted the end correction which was the inside diameter of the tuner . Replaced tuner and wound it to physical length.

Result : Exactly the same setting on the tuner as the setting that my gun smith had set and test fired those great targets. Like exactly the same setting which astounded me.

Tonys system works and works well ,Enough said.

Kind regards Ben
ps however there is still a small issue with factory barrels 20 inches long like the Anshultz 2013 because I can not work out how to get the system to work with that shorter length . We all know that the Anshulz rifle is a fine shooting rifle.



Just by chance, I used the 5th harmonic on my Air Rifles that have 19" barrels and that worked spot on for them. I used it because it provided the shortest length attachment and it made both of them shoot wonderfully. Perhaps it's going to be lower harmonic for shorter barrels and higher harmonics for longer barrels?

Bill Wynne
12-01-2013, 10:21 PM
Tony (PacRat)

A fellow shooter, Bobby Williams, came over and we got out my rifle which I though was right on. I was pleasently suprized. By your formula it was less than 5 clicks off. Our measuring was with a cleaning rod and a sheet metal ruler and then with a dial caliper. It was very close but less than perfect measuring. You have sold me.

Concho Bill

Evelio
12-02-2013, 12:30 PM
Tony
The barrel in question where the PRX did not work is 21.947 long using the 9Th. harmonic, I will try using the 7th harmonic this week.
How about trimming 1/2" from the Harrel inner tube ?
Evelio.

Charles E
12-02-2013, 01:40 PM
The Purdy Prescription did not work with my 24 (actually, 24.02) inch barrel. Tony did check my calculated numbers, but of course, he didn't do the actual measuring, so there could be an error there.

In passing -- one thing Tony mentioned y'all might have forgotten is the "barrel length" is just that. If you're measuring using a cleaning rod to the cocked bolt, you have to subtract the head space, which would be around .045 inches -- much larger than the crown. If the firing pin is "down" & the cleaning rod a large diameter one, that might give actual barrel length.

Perhaps the problem I have is that with the 24-inch barrel, the movable weight (having the large diameter tube) sticks out only .2 inches beyond the small-diameter tube. In that case, according to the prescription, you use the diameter of the small tube, so EC = .186. Were the small diameter tube shorter, then the .402 EC would be used. I was going to try that anyway, but unfortunately, using that calculation winds up beyond the adjustment range of the Harrell's tuner I have.

I went back to my old spot, where there is no vertical change between Eley Black Box 1043 and 1054, Midas+ (sadly also 1054) and the older SK Rifle Match, speed unknown. I really need to get some 1070 Eley...

* * *

I'll allow I don't undersand the Purdy Prescription. You're moving a large, indeterminate mass so it's front end is at a certain point. This says nothing about where the center of mass of that adjustable portion is, and doesn't seem to really correlate with a useful waveform or harmonic -- esp. as the tuner is not that rigid to the barrel. Still, if it works, I don't really care that I don't understand, though it is frustrating for an old analog-era recording engineer...

Fred J
12-02-2013, 02:43 PM
I've done several barrels of my own as well as others. So far, the Purdy Rx, works better than any other method I've tried in the past, and at a much lower cost. I took a brand new barrel yesterday and shot 19 out of 20, 10's. On the second target after moving the tuner two clicks, I shot 20, 10's with 17 X's. Barrel is 25" long. Then with a 28" barrel I had the crown recessed, to the 17th harmonic, I shot a 250 with iron sights. Not as tight a group as I would like, but it was good enough yesterday. I have a 22" I will try next. Any way, Tony stated in the beginning, it was hopefully a new method of tuning that would help tune with less cost involved.

I'll add one more thing. I have used both 5oz Harrell Tuner as well as the normal 8-9 oz. As long as the length the Rx calls for set, the tune comes in with in 10 clicks. Most have been 2 to 5 clicks. I haven't found any difference by using heavy weights as long as the length is what you need is achieved. Most of mine have been Aluminum extensions.

Doug
12-02-2013, 05:18 PM
My understanding is the PRX is based on a closed tube.
Thus we are only concerned in the thickness of the brass & not headspace.
If you can measure in the 100's of an Inch then put a spent cartridge in the rifle before measuring.
Make Sense??
Otherwise just measure to the bolt & you will be close enough for "Government Work"!

I am bringing my computer to the ARA Nats this weekend to do some testing.
I wrote an excel program that will do all the calculations for me & if anyone wants to play with it look me up.
(I sleep by the wood stove so just wake me up if after hours!)

Doug
12-02-2013, 05:36 PM
Over the years if I ever removed my Tuner I felt that it was out of tune when I reinstalled it!!
Thus if your rifle is 'close' to tune then do your best to measure with the tuner on so you have a base line to use for comparison.

Fred J
12-02-2013, 08:34 PM
Here is a little tool I use to help me get my tuner back where it belongs after I remove it for a complete cleaning. Also great for double checking your setting after transporting or leaving it unattended between targets. I have accidentally moved the tuner when moving or casing.
http://i150.photobucket.com/albums/s86/FredJ_2007/HallOctTune_zps2311feaf.jpg (http://s150.photobucket.com/user/FredJ_2007/media/HallOctTune_zps2311feaf.jpg.html) http://i150.photobucket.com/albums/s86/FredJ_2007/TunerTool_zps8684ef97.jpg (http://s150.photobucket.com/user/FredJ_2007/media/TunerTool_zps8684ef97.jpg.html)

Simple wooden dowel that fitted to conform to the muzzle opening and marked for the harmonic you want. Just insert the down into the tuner until to centers on the bore, and turn the tuner to the desired mark. I made one for each barrel I've tuned this way.

Charles E
12-02-2013, 08:56 PM
My understanding is the PRX is based on a closed tube.
Thus we are only concerned in the thickness of the brass & not headspace.


What I wrote Tony in an email, November 18, 2013:

I notice you get quite careful with the physical length of the barrel, to the point of subtracting a value of .010 for an 11-degree crown, to arrive at the position of the end of the bore.


Yet at the other end, you recommend measuring to the boltface. When you think on it, that's barrel length plus headspace. So, you're not considering the barrel as a "beam" *(as in "single cantilevered beam"), but a tube, capped at one end by the cartridge case.

What he wrote back:

I could have sworn that it was mentioned that you have to remove the headspace if you measure to the bolt face...

Edit:

That last bit wasn't in the MS Word document he sent me. Which isn't to say you're not right & I somehow intercommunicated what I was asking Tony. The single cantilevered beam model does have problems -- e.g., what "length" do you use if you're barrel blocking?

Fred J
12-03-2013, 12:47 AM
Charlie:
I purchased some 1/8' X 36" wooden dowels. I used a spent case in the chamber and inserted the dowel into the bore until it rested inside the case pushed up against the bolt face. I then marked the dowel at the exact point it exited the bore. That will give an exact barrel length number to work with. If I'm measuring a barrel that is finished, but not installed, I just measure from breech to muzzle, and have not had a problem with the numbers. I've never been out of tune by more than 10 clicks. This is so easy, it's like stealing food at a free dinner.

The Jet
12-03-2013, 01:58 AM
I will try and give the lower harmonics a go for the shorter barrels Thanks for that guys
Seems that sometimes its hard to get the right length that will fit the tuners movement range
I know some off you guys have cut a Aluminuim tube to length . How did that work out ?

kind regards Ben

Pete Wass
12-03-2013, 03:32 AM
14370
I will try and give the lower harmonics a go for the shorter barrels Thanks for that guys
Seems that sometimes its hard to get the right length that will fit the tuners movement range
I know some off you guys have cut a Aluminuim tube to length . How did that work out ?

kind regards Ben

With both my Air Rifles I made simple tubes, one from aluminum and one from steel electrical conduit. Both of them worked exactly the same. I question the need for a lot of weight, a-la a Harrels type tuner. Having a threaded link with the tube for tuning would be a nice touch though. I may try to make one this week. In fact, I am going to make a tube up to use in place of the Harrels on my best shooting rifle to see if the tuner is actually needed.

Pete

Kim Cosstick
12-03-2013, 06:07 AM
Hi Guys.
If I use a 1" ID tube what end correction would I use.
Kim

Jerry W
12-03-2013, 09:36 AM
Kim, the EC = .3 X the I.D.

So if it's truly 1.00" I.D. it would be .3 X 1.00 = .3 EC.

Jerry

The Jet
12-03-2013, 11:44 AM
I think that would be a great idea to see if it works or not then maybe someone can come up with a pretty one that can be docked to length and not cost he earth.
This would really ell a lot of guys out that presently can't tune their Anshultz 2013s and whatever other popular rifles being used. Lowey a company in Australia is about to release a new tuner for smaller diameter barrels i.e. Anshultz 1712 I have one on order and will report back as soon as I get it . The release date is will be before Christmas as they are presently being inscribed with calibration numbers.
Kind regards Ben

crb
12-03-2013, 11:45 AM
UPS just dropped off some 6061-t6 stock from Aircraft Spruce. I am thinking of an outer body threaded for Gene Beggs tuner rings that I have laying around unused. This outer tube will be quite a bit shorter than the PRX tuner length. The thinwall tubing will slide into the outer tube and make possible easy and cheap tune length changes.

The lower LH tube is 1" OD x .750 ID. The upper tube is .750 OD. All this is from Aircraft Spruce.
http://i114.photobucket.com/albums/n260/raayjayy/Tunertubingall3_zps3c0d06cd.jpg

The .750 OD tube slid into the .750 ID tube
http://i114.photobucket.com/albums/n260/raayjayy/tunertubingslidetogether_zps6f86a1fb.jpg


The .750 OD tube slid into a thickwall .750 ID tube I got from MSC.
http://i114.photobucket.com/albums/n260/raayjayy/tunertubingtunerbodystockslidetogether_zps3e8df596 .jpg

Kim Cosstick
12-03-2013, 12:17 PM
Thanks Jerry.
Kim

PakRat
12-03-2013, 01:46 PM
Hi All

Do to a medicalproblem I will not be able to participate as much as I would like. I am having difficultiy concentrating and watching the screen is difficult.

As things permit, I will try to watch whats going on.

Tony

Vibe
12-03-2013, 03:17 PM
Hi All

Do to a medicalproblem I will not be able to participate as much as I would like. I am having difficultiy concentrating and watching the screen is difficult.

As things permit, I will try to watch whats going on.

Tony
Hopefully it's "only" vertigo - which is bad enough, but will go away (I know)
Take care of yourself and get well. Give me a shout when you get your sea legs back under you.

crb
12-03-2013, 03:32 PM
Hi All

Do to a medicalproblem I will not be able to participate as much as I would like. I am having difficultiy concentrating and watching the screen is difficult.

As things permit, I will try to watch whats going on.

Tony

Good luck.

The Jet
12-03-2013, 08:12 PM
Hope you get well soon Tony I hope that it isn't anything to bad but know our hopes and prayers go with you mate.
That tubing looks like the sort of thing that is required all right Ray. Please take some photos and let us know how it all works out.
kind regards Ben

Rambo
12-05-2013, 02:01 AM
Hi Tony,
I hate to hear that, you get better for sure!! Be checking on you later!!!
YBRF!! Rambo (Douglas)

Mak
02-05-2014, 04:59 PM
I recently purchased a new falcon ,shillen barrelled benchrest rifle in Australia. Which the smith a Australian champion shooter set the tuner on and test fired 5 shot groups of less than 0.3 inches at fifty metres in windy conditions. When I received rifle being a complete newby I photographed the turner setting and set about using Tonys system to test his tuning settings. Since we live in a country that uses millimetres instead of inches. I simply converted the end corrections into metric and removed the Harrel tuner . Took the barrel length to the closed bolt using the ninth Harmonic I calculated the harmonic length. Then subtracted the end correction which was the inside diameter of the tuner . Replaced tuner and wound it to physical length.

Result : Exactly the same setting on the tuner as the setting that my gun smith had set and test fired those great targets. Like exactly the same setting which astounded me.

Tonys system works and works well ,Enough said.

Kind regards Ben
ps however there is still a small issue with factory barrels 20 inches long like the Anshultz 2013 because I can not work out how to get the system to work with that shorter length . We all know that the Anshulz rifle is a fine shooting rifle.

Hi Ben

Please check PM

cheers
mak

Fred J
02-05-2014, 06:45 PM
Try the 7th harmonic. Should work.

Flat Land
02-05-2014, 11:45 PM
Lower harmonics work well, the formula is the same except for the number you divide by and multiply by. For the 7th divide by 6 and multiply by 7, I've even tuned to the 5th harmonic, divide by 4 multiply by 5.
Pressing a tube into a removable weight on a H/H tuner allows you to make adjustments to the length with or without adding weight.

The Jet
02-06-2014, 05:02 AM
I have replied to your pm