Testing new discovery

[mr007s]

Sounds good,  I will be watching for your results.

[Hobbyman2007]

I still have mine mounted to my K550 . It doesn’t come off that gun as it just shoots so well and I don’t want to mess it up . I was thinking of making another but I don’t have the material right now . Next time I head to the steel yard I’ll get some more tubing .

[rsterne]

I have another barrel coming for my Disco Double.... a 26" long TJ's .257 cal with a 14" twist.... The gun has a Cothran valve, and should be able to get decent performance at 3000 psi with 60-70 gr. slugs.... The barrel is 1/2" OD, which is perfect to fit into the receiver, which has a stub for a 7/8" OD CF tube used to tension the barrel.... It currently looks like this, except the lower double tube is now blued.... I currently have .22 cal, .25 cal and .30 cal barrels for it....



I don't have any more Hatsan Air Strippers, but I do have some 1" OD x 1/2" ID Belleville washers that are 0.049" thick.... A pair of them take 1200 lbs. of force to compress flat, and three such pairs in series will do that with a travel of 0.075".... If I use 1/2"-20NF thread on the muzzle, 1 turn of compression works out to 800 lbs. of tension on the barrel.... I decided to make a lead shot damper that doubles as the tension nut.... It will look like this.... The outer sleeve of the damper is 1.50" OD x 0.035" wall 6061-T6 aluminum tubing, and the body/spool will be machined from 6061-T6 bar stock.... with the assembly sealed by O-rings to keep the oil from leaking out....



With the damper 3/4 full of lead shot, plus some power steering fluid, the damping mass will be about 6 oz.... and the total weight of the device roughly 1/2 lb.... With that for damping, plus the ability to vary the tension on the barrel.... I think it should work quite well.... 

Bob

[rsterne]

The Motel is slowing down as it does this time of year, so I finally had some time to get back in the shop.... One of the projects that has been waiting is some new dampers for existing PCPs.... This one will fit my .172 / 6mm Regulated gun that I built over the last couple of years.... You can see the present harmonic tuner on the muzzle....



It can be screwed onto the threaded steel sleeve on the muzzle, and adjusted back and forth in the same manner as the brass weight.... Here are the parts....



The brass weight is about 5 oz. and the threaded steel sleeve that attaches to the muzzle is about 3 oz.... The spool and tube that covers it are both 6061-T6 aluminum.... The spool is drilled 15/16" ID to clear the threaded steel sleeve, with the front end threaded 15/16"-28 to match the sleeve.... The OD of the center of the spool is 1", and the tubing is 1.50" OD x 0.035" wall, so the ID is 1.43".... The spool is 2.25" long between the flanges, which are sealed to the inside of the tube with O-rings, and the LOA is 3.00".... The 8-32 SHCS is to retain the tube from sliding, and it also has a short piece of Delrin rod under it that presses on the sleeve threads to prevent it from spinning, yet leave it adjustable....

To fill it with lead shot, I positioned it so that 25% of the inside length (9/16") was between the top of the tube and the inside of the spool flange, and filled it with lead shot.... so that the inside volume is 3/4 full of shot....



I then slide the spool in further so that it looked like this, with just a small gap for the oil to run into....



I submerged it in power steering fluid (about 10W) and shook it around until no more air came out.... and then slid the spool down into its final position.... Adding the screw (and wiping off the oil) completed the assembly....



The damper weighs about 8 oz. total, with about 5 oz. of lead shot inside, damped by the oil.... It will be a while before I get to try it out, but I can now interchange it with the brass weight, and both have over an inch of fore and aft adjustment on the muzzle....

Bob

[T3PRanch]

Very nice Bob!
I have to rebuild mine as it leaks oil like an old car with 500000 miles! lol

[KnifeMaker]

Fantastic workmanship Mr. Bob!


Mike

[KnifeMaker]

I've yet to try a MAD device on the .223 barrel. Humm--Maybe tomorrow. Having trouble getting the power I want. The barrel is 2- inches. Seems way down on power compared to the .250 barre. So much less area to push on.


Makes me really wonder how I can solve the issue with the .172 barrel I have here. Limited to 20" and only a 3200 fill It will undoubtedly be even worse on power. GRRRRR!!!


Mike

[rsterne]

Mike, my .172 cal is regulated at 2800 psi, and blows those 26 gr. NOEs out at well over 1000 fps from a 28" barrel.... However, you are correct, when it comes to all out FPE, barrel volume and pressure are the key.... Fortunately, it isn't all about FPE, only achieving speed into the 900s with the bullet you want to use.... Smaller calibers mean lighter bullets, and less FPE (and air use) for a given velocity....

Bob

[rsterne]

I made another damper today, this one for my unregulated .224 / .257 PCP.... It will also fit on the .172 / 6mm regulated PCP, but not vice-versa, the long one I made yesterday will not clear the front of the air tube....



Anyways, the difference to yesterdays damper is that this one only fits over the 20mm OD carbon sleeve, and mounts to the 1/2"-20NF threads on the muzzle.... The threaded portion is about in the middle of the damper, with the back counterbore fitting over the tube, and tightening against the internal shoulder in the damper.... and the front portion is also drilled to 20mm so that the HPA escaping from the muzzle won't disturb the flight of the bullet.... Here is the front view of both dampers....



Both dampers are 1.50" OD, but the one I made today has a smaller diameter for the spool, only 0.86" instead of 1.00", because the hole through the damper is smaller.... This means that I could make it shorter to keep the same weight....



It is only 2.50" LOA, instead of 3.00".... but still weighs the same at 8 oz.... So, now I have two dampers, one adjustable and the other fixed, along with a pair of the brass harmonic tuners.... Once I get a chance to do some serious shooting with these two PCPs, in the four calibers, I can also do some testing of the shot-filled dampers.... C'mon 2021.... 

Bob

[KnifeMaker]

Mr. Bob, I really like the looks of those. Fingers crossed for them.


My post was a bit badly spelled. The bbl. is only 20" in order to fit the factory shroud. I do have a much longer shroud here and tested it. but after bumping in on every thing in the house getting it outside, I gave up on the "Marlin Pole." LOL


Mike

[rsterne]

I made another damper yesterday, using 1.25" OD x 0.035" wall 6061-T6 tubing.... This one fits over a 5/8" or 16mm barrel, or a 1/2" one with a CF sleeve.... This will fit a LOT of the PCPs I have.... The slimmer shape looks better, IMO....



The threads are for 1/2"-20NF, and it is 3.25" LOA.... The spool is 0.73" in diameter.... It weighs 7.5 oz. complete, and contains 5 oz. of lead shot when 3/4 full.... I am sure looking forward to retirement, I have so many things to test.... 

Bob

[Nvreloader]

Bob

Very nice build, will be awaiting the test results.

A question for you,
What size shot are you using 7-1/2 to #9,  I have a small bag of #12 shot, used in the RF shot shells,
bought it several yrs ago........for making Snake shells for the 38 Spcl pistols.

Would the shot size make a difference in weight adjustments, as only sizes will fit between the spool shank and walls etc?

I am still using the 6oz Mercury ones on the QB and Guantlet, with great results..........

Thanks,
Don

[rsterne]

I use # 7-1/2 shot.... I made sure that the gap between the spool and the ID of the tube is greater than twice the shot diameter, so it can't "jam" in between and is free to move.... Therefore the smallest gap I use is 0.215", because the shot is 0.095".... I can't see any penalty in going to a smaller shot size, I just used what I have, and designed the gap accordingly.... Mercury would be a great choice, and the device can be made smaller for the same moving mass, as it is nearly twice as dense as lead shot.... 

Bob

[KnifeMaker]

I use to have quiet a bit of mercury. Long gone now. Never had a use for it. Wish I still had it. Would be a natural for this.


Great looking devices Vr. Bob!


Mike

[TF89]

I have been out of this thread for awhile, about 15 pages worth .  Those are some great builds Bob and I'm looking forward to your results. 

[Airgun-hobbyist]

As I see it, here are some of the variables....

Variables affecting the force, acceleration and vibration generated:
FPE (further broken down into)
Bullet weight
Rifle weight
Velocity (critical in determining when the bullet arrives at the muzzle, relative to node location)
In addition, possibly air pressure and dwell (how they effect the vibration and bullet arrival time at the muzzle)

Variables affecting the frequencies and modes of vibration of the barrel:
Barrel OD (stiffness varies with the 4th power)
Caliber (larger bore reduces stiffness)
Barrel Length (longer reduces stiffness)
Material (ie how the dimensions relate to the stiffness)
Barrel Supports (ie free floating, or bands and where positioned)
Direction (plane) of primary barrel vibration (ideally should be vertical)

Variables affecting how the Damper/Tuner interacts with the node location and amplitude of muzzle movement:
Mass of Damper/Tuner (increased mass decreases amplitude and frequency, and decreases horizontal movement)
Position of Damper/Tuner (lengthwise and radially)

Variables affecting the damping effect of the material inside the Damper:
Damping Material (Mercury, Lead shot, powders, fluids, masses on springs, etc.)
Shot/particle size
Fluid viscosity (if any)
Fill ratio of Damper
Internal Shape of Damper
Mounting Position
Any use of springs (mechanical or magnetic)
Mounting method (ie solidly, rubber, etc.)

While it is possible to look at these items one at a time, to a large degree they interact, and changing one thing affects one or more of the others.... I have neither the brain power, or the computer power, to even try and sort through predicting how a given damper/tuner will work on a given rifle/pellet combination.... If you do, then more power to you.... If you don't, then jump in there, build something, and try something to increase our database of knowledge.... 

Having said that, I believe that more powerful PCPs may require a larger damping mass.... and the more flexible the barrel, the more effective the damper may be....

Bob

Here's my contribution to KnifeMaker's MAD concept.  This configuration, being tunable for weight, viscosity, solving the gravity issue of a large tube filled with settling shot, may work to place a damper on recoil as well as placement along the barrel or moderator to dampen barrel whip and therefore tighten group size.  It could be mounted in a rubber cylinder type boot, with up to six tubes, or it could be solidly clamped in this type of configuration, depending on the rifle's needs of course. 

Don't mind the BB's and pen bodies, and springs, if made with stainless steel tube then an o-ring and threaded cap can seal the tube. 

As for weighted materials, I'm thinking Tungsten carbide bearings for smooth operation or cheap lead shot, your choice. 

The spring should be as light as possible, only to keep the weight centered and allow inertia damping working in both directions. 

The springs, damping fluid, tube size and shot size will determine the rate of movement.  And of course all this depends on the recoil of the particular rifle and what is required there to tame it. 

This tube system can be filled with Mercury as an alternative to tunability based on felt recoil.

Once the recoil is tuned, then comes the process of placement tuning of the device along the length of the barrel or moderator to change the barrel whip for smallest grouping. 

If the tube damping system was engineered well, it could be placed into service on Bob's genius threaded bushing system with that 28tpi twist rate to fine tune placement.

What do you think?

[Airgun-hobbyist]

Bob, picture your part made in stainless steel, a little longer for more volume, drilled with multiple cylinders around it's circumference that can be filled with Mercury and capped.  It would reduce recoil and fine tune barrel harmonics all in one unit.

[Insanity]

I use to have quiet a bit of mercury. Long gone now. Never had a use for it. Wish I still had it. Would be a natural for this.


Great looking devices Vr. Bob!


Mike

FWIW you can purchase mercury rather cheaply now.

[BackStop]

I use to have quiet a bit of mercury. Long gone now. Never had a use for it. Wish I still had it. Would be a natural for this.


Great looking devices Vr. Bob!


Mike

FWIW you can purchase mercury rather cheaply now.

What is *rather cheap*?

Here is one listing on Amazon...

$30 for less than 2 ounces just doesn't sound cheap to me for some reason.   

Here is one at $29 for 100 grams... 

Still doesn't sound cheap to me.   However, I have NEVER bought mercury.  (chuckle)


Oops, that last link was for Gallium... oops... 



 

[Insanity]

That's about going rate other places charge more for 50g.

https://www.albochem.com/product/mercury-metal-9999-pure-50g/?gclid=CjwKCAiApOvwBRBUEiwAcZGdGHillrMujhfDzw26Pa6V1-x8eDqivHzrWrEzrkPpSkJRzIe53_xqoBoCfuYQAvD_BwE