Questions also tell me that people are not really up to date about where the research and development of spring guns is going. In a way, that is understandable, manufacturers are not doing the best of jobs in telling people how more advanced today's spring guns can be in relation to those airguns that the Cardews' analyzed in their legendary works.
So, let's look at a little bit of history and how it percolated into the production line of one of the foremost examples of applied technology in the spring-piston airgun world, then we'll look into more recent experiments, and how, finally, the product became a system to be included into the new edition of the Air King (the AirKing Pro). Along the way, we'll discuss how sometimes even manufacturers fail to recognize the DIFFERENCES between an airgun and a firearm.
So, let's get started:
A bit of history
Therefore, when I came across a commercial unit that offered to do that for the DIANA's I jumped into it. Over time, I found the unit somewhat fragile and capricious (getting out of adjustment at the worst possible time), till at some point, I had it glued (this commercial Harmonics Tuning product was discontinued about 15 years ago), then in 2015, as a result of its dismal failure in a WFTC Match, I decided to design something that would work in my favourite platform, the DIANA 54 AirKing.
Some time passed and I then came onto the realization of a basic characteristic of the DIANA 48->56 family: The barrel is in reality a 15.2 mm's barrel that has been encased in a shim and then that shim goes INTO an 18 mm's sleeve, that is what we see. That is the nicely blued part that we take for a barrel, but it is not.
In the past, SOME shooters used to fill the cavity between the shim, sleeve and barrel with resin, or other compound, and claimed to have improved the accuracy, but my problem with that approach was that it was a FIXED solution. "Tuning" of your system would STILL need to play with the MV and finding the "right" pellet.
I wanted a simpler device, something that would allow you to re-tune the gun should you change pellet batches, or wanted to change brand, power level, or any other thing. Something that would allow you to set a velocity (according to some rules, or other criterion set by YOU), and then tune the gun to THAT. In other words, command the gun and not be commanded by it.
I looked at all the existing Harmonic tuning systems (firearms, archery, and airguns) and all but one depended on a weight that was knurled and screwed or unscrewed along some position in the barrel, or a rod. The one that didn't, depended on moving the support position of the barrel in the stock (forend pressure point bedding) therefore lengthening or shortening the free-floated length of the barrel, problem was that most spring-piston airgun barrels are free-floated by design.
So, I decided to combine both concepts and came up with a system that is comprised of a specifically dimensioned weight that can move back and forth along its position on the barrel with set spacers.
I worked through a few prototypes and when I had settled on something I published my results here in this blog entry.
Now, do note that this happened in 2016, that's 4 years ago!
Since then, most of CCA builds have benefited from this "gadget", and/or from the knowledge and techniques that this research brought. Further research has been done and now we know not only how to control, but how to REDUCE the harmonics at barrels' muzzles (though that is another story ;-) )
Almost three years ago, I started working closely with DIANA, and since there were talks to bring this technology (and others) to the public/shooters of DIANA airguns, I did not pursue further the commercialization of the product.
So, when the time came to write the spec for a "new" 54, it was normal for me to include this device into the spec. In complete agreement with DIANA, we decided to name it the HPM (for High Performance Muzzleweight).
The first appearance of the device to the public under the DIANA brand was at 2020 SHOT Show, there is a whole thread about it here where you will find links to videos, reviews and other comments; as well as a lot of questions and answers.
And that brings us up to the present
First proposal and a "failure"
The problem was that there was NO BUDGET available for improvements. Meaning that whatever we wanted to put in, had to come from reductions and savings in the SAME model, that is a tough value-engineering problem: Improve a product AND make it cost the same or less. Not easy without a technology leap. Still the challenge was taken up by the team and we discussed a number of things that could be improved. Sadly, ALMOST ALL implied some cost increase. The exception was the Harmonics Tuner. A muzzle piece needs to be there, and the plastic one in current production, though not expensive, is not cheap either. It's a complicated mould. Also, the change COULD imply that the "Pro" model would be a scope-only rifle, so the sights could also be eliminated. Lastly, there was an extra operation on the barrel to create the "key" where the front fight ramp/muzzle piece needs to index to always keep the front sight straight up. Between all these "savings" the Harmonics Tuner seemed to be a good candidate.
It also promised to be the most value for money that would still be useful to ALL shooters (and here I want to remind you that DIANA operates in more than 90 countries with 7 different power levels and some caliber/rifling/OAL legal complications).
And, finally, adapting it to the EMS system would be a breeze, so, after much thought, the concept of the Harmonics Tuner came to the forefront. The part is simple to make and easy to use, it does NOT come out of adjustment, and use tends to affix it more and more firmly into its place.
Simultaneous to that I had started some serious work with a friend with a scientific penchant that tested the usefulness of the Harmonics Tuner in two completely different power plants: A short stroked D56 and the "skinny piston" (22 mm's compression chamber bore) version of the same gun. As different as apples and oranges.
You can read the results of those experiments here:
As you can see from the whole SAGA, the Harmonics Tuner proved its usefulness in two completely dissimilar engines. It would be like testing a turbo-charger in a Mack Diesel Tractor Trailer and a Subaru BRZ and still finding improvements in both results.
And the HT was deemed an "easy to use" device, needing the release of the screws, the addition or subtraction of an ORing and the reassembly of the gun, an operation that took less then 3 minutes per test.
So, it was DOUBLY annoying when DIANA's head gunsmith told me that they had not found any change in group size when tested in the factory, regardless of the number of spacers added. WHAT?
Luckily, the Technical CEO told me that they would still go ahead and planned the use of the device, but that I had to come up with a new design, test and a procedure to demonstrate the usefulness.
After taking a day (or two) to calm down and analyze the whole thing, I decided to question the test procedure followed by the factory. It was then that I was told that the gun had been put on a vise that held the sled system fixed, but at an angle, that changes had been made from the original spec (aluminum instead of steel), and that only two screws, instead of the 6 that were originally specced had been used, granted that perhaps my drawing had not been completely clear, but still the device built by the "Construction" section of the company was not what I was talking about, these substantial changes warranted a re-design and re-test, under conditions that would be found in real life shooting.
And here is where there is a lesson: If you need to test something that is going to be used under field conditions, then test it under the same field conditions.
A new material was sourced as Aluminum DOM bar, and new prototypes were made, but this time complying with the needed weight (one of the most lengthy sets of experiments I ever conducted way back in 2015).
I then prepared a completely new test using one of the guns that were on the pipeline, and these were the results:
With these results in hand, I went back (electronically) to DIANA, and it was agreed that the AirKing Pro would come equipped with the device.
The device itself is VERY simple and easy to make. From the outside it looks just like an average Muzzle Weight, but the trick is on the inside, where ORings can be added or removed to determine the position of the weight along the muzzle. In the same way that using a longer or shorter bar changes the "tone" of a grandfather clock carrillon, the harmonics (vibrations) at the muzzle also change and this is what determines the POSITION of the muzzle and WHERE IT IS AIMING AT, when the pellet exits the muzzle.
Using one of Steve's excellent pictures, although that is a steel version of the HPM for the model 56, not the 54, you can see the make up of the whole system
But the principle is the same: You add or delete ORings to bring down the group size with the pellet you want to use (within reason).
As it was demonstrated and re-tested, in a normal 54, the results were verifiable and repeatable:
There will be other options in stock colors and, of course, a beech version.
The process to "tune" the rifle's harmonics will be the same:
1.-Start from 0 ORings
2.-Shoot three shots into a "waste" bullseye
3.-Shoot a 5 shot group at least 15 meters away (19 is preferrable).
4.- Add one ORing
5.- Repeat from 2
6.- Repeat from 4
When you reach 10 ORings, STOP, you should see a "periodicity" each 4->6 Orings (depending on power level), settle on the two settings that are most promising and re-test till you are happy that you are at the best possible point.
I would advise to "Run in" the rifle BEFORE the tuning (if in doubt about what is the BEST way to do this, read this), as the wearing in of the parts amongst themselves is an essential part of what airguns need to be able to deliver top accuracy, but if you want to "train" yourself in the procedure by all means do it several times. Just understand that, in the end, you cannot put the carriage before the horses.
Hope this answers as many questions as is normal before seeing/handling the actual thing.
Always open to questions or comments.
Keep well and shoot straight!