OzFclass

Back a good few years when TR teams were required to use NRAA factory ammo, it was common for astute shooters to tune their rifles by adjusting the position of the foresight until they achieved the minimum grouping out of that load, then tailor their daily handloads to replicate that condition. This mightn't have been the earliest tuner around, but it was revolutionary in the TR field. Stu Mowat became the local specialist & many of the top shots would get him to set up their barrels for them.

I watched him one day as he worked one of Bill Martin's barrels for him. As he adjusted the foresight position, the group would move from a vertical string to a dot to a horizontal string, albeit both strings having an amplitude in the opposite direction. However, getting that dot group to stick was a challenge & Stu ran the test many times before he was satisfied.

Tony Boyer, in common with many short range benchresters favours a group with an element of vertical in it, their belief, as far as I can make out being that they can thus avoid a rapid transition to horizontal stringing that might/can/does occur to their high intensity loads with atmospheric changes.

The ultimate challenge for us is to master barrel harmonics to achieve fine accuracy by the most reliable means that we have to hand.

I certainly am no expert on this matter and was going to sit this one out but after reading a bit thought I would just put my 2c in. I actually believe everyone posting so far has hit the nail on the head in one form or another.

My thoughts:
1) Yes vibrations do go down the barrel in all directions. One of our shooters actually tunes at 25m - and I have done a little bit as well - and he often states the groups go horizontal then diagonal then vertical then pinhole (maybe not in that order) but the vertical are the biggest component.
2) As Cameron hinted I also believe there are a lot of good reasons why the vertical component is the largest and this has a lot to do with rifle design. For example: A sporter action working off a front recoil lug in a heavy stock (e.g. loaded up with lead like some of us do to tame the recoil) can impart a massive vertical moment under firing. The recoil lug in front of the action lugs (expansion area) imparts a large force on the heavy stock resulting in a large vertical component. There are generally other action asymmetries (such as take down screw holes and scope mounts) that cause asymmetrical expansion generally in the vertical plane as well (except gas port) and also as pointed out the barrel is under static load - as the pressure runs down the barrel this results in a vertical drive. The lighter the action and barrel the worse these will be.
3) Another "vibration" is the pressure wave (bubble) that travels down and effectively "opens" the bore. See varmint Als website for some good diagrams.

A lot can be done for all of these components in the design of the rifle BUT in saying this - all rifles can be tuned. Some examples of rifle designs e.g. 1) large diameter barrels reduce P wave amplitude so bore does not expand as much. 2) remove asymmetrical recoil lug systems in front of the expansion lugs (barrel blocks, tube guns, mid to rear recoil lugs and glue in actions etc etc). 3 Heavy metal work and light stock. 4. smooth bags so they move quickly and freely. etc etc.

As long range shooters it is very hard for us to discern the small horizontal components from the wind.
MORE IMPORTANTLY: most "ladder tuning" isn't done to avoid vibrations but actually use the vertical component to maintain a vertical flat line over a wide range of velocity. This cannot be done with horizontal components.

ALSO "P waves which actually do scatter in all directions will show up on a vertical ladder even though they are affecting both directions.

Thanks Dave - good observations. Keep them coming. Hopefully we can squeeze a bit more out of Cameron .

With the Border simulator (thanks Aaron - very interesting), if you put zero distance between bore axis and C of G of whole rifle, you get no barrel vibration. Except for the bolt and its opening, and maybe a cheek piece, most rifles' C of Gs are only slightly offset horizontally from the bore. Does this explain why horizontal vibrations are less in magnitude than vertical. And extending that idea further, if you had a low profile, light-weight stock and heavy high-mounted scope you might be able to significantly reduce vertical vibrations?

Alan

Quite possibly Alan - not to mention the added bonus of reduced torque roll (overcoming offset weight is far more beneficial than an offset stock) but there would be tremendous torque and recoil forces on the scope mounts and scope.

The real question is - for 1000 yard compensation we may well want to induce a "massive" vertical component of a certain frequency - how do you do that???? Is it possible to create a "near perfect 1000 yard rifle"??? - Anyone want to fund an experiment? - I have a few neat ideas and have modeled some up that look quite good.

DaveMc wrote:-for 1000 yard compensation we may well want to induce a "massive" vertical component of a certain frequency - how do you do that???? Is it possible to create a "near perfect 1000 yard rifle"???.

Dave,

I've thought about a weight on a pole extending well above the scope. Would need to be rigidly attached, possibly from both sides of the scope rail area, and the sliding weight could be adjusted vertically as a tuner. It'd look pretty strange, but people say that about my stocks already .

Alan

What happens when you put the barrel under compression as opposed to leaving it as a single pinned beam?

AlanF wrote:Thanks Dave - good observations. Keep them coming. Hopefully we can squeeze a bit more out of Cameron .

Alan

Geez Alan your putting the pressure on. I love these topics as the answers are not easy and pure science does not always make things clear cut. There are so many variables with this one subject that Denis kicked off.
One thing I learnt in a big way last year was to concentrate way more on 1000yd accuracy. As like many I attend a lot of prize shoots that are mid range. 300y to 700d, sometimes 800yds. Getting rifles to be competitive for these ranges requires work but once you find the formular it will usually work week in week out.
Maintaining accuracy at 1000yds is a different story. This is where more variables come into play and existing ones get magnified. I have always been intrigued by barrel tuners. I made a heavy tuner for a relatively light 7mm barrel I received. The idea was mainly to add weight. Maybe I just got lucky but the tuner certainly did not harm accuracy and added the weight I wanted. I was able to find reliable accuracy at 1000yds and it would shoot 60's at 300yds with the same load. Like I said the tuner is heavy and I believe it plays a major role in the way the barrel behaves right from when the projectile starts to move. I have used Bergers and Sierra's with excellent grouping. This barrel will hold the 6 ring for 20 shots at 1000yds. I shot it a few weekends ago in 40c heat. 22 shots with no vertical issues. I won't rave about the horizontal though . A good friend tried the same heavy tuner idea with a barrel he was having trouble tuning with a particular batch of 2209. The tuner turned the barrel into a match winner with the same powder batch.
That better do for now. Getting off topic, sorry Denis. Later I want to tell a story about a rifle I have that turns good barrels into tack drivers.

Not a clear pic. The tuner is 1.5" diameter stainless.



Cheers

AlanF wrote:I've thought about a weight on a pole extending well above the scope. Would need to be rigidly attached, possibly from both sides of the scope rail area, and the sliding weight could be adjusted vertically as a tuner. It'd look pretty strange, but people say that about my stocks already .

Alan

If you have ever been involved in target archery, you will notice the long stabiliser rods with weights that stick out in front of the bow. These act to slow down the movement of the bow on release so that the arrow can get clear of the bow and not have its flight upset by the movement of the bow under recoil. Some of these stabilisers are quite compact and have advanced internals to overcome some of the issues associated with longer stabilizers.

A similar compact stabilizer (or pair of stabilisers) could easily be attached to the barrel or stock of a F-Class rifle and should provide significant dampening effect to counteract the movement of vibration, recoil and rotational forces on the rifle.

The best part is that they are readily available from all good archery shops, so no design and development work needs to be done. Be interesting to see what effect they would have.

Dont be sorry Cameron, I've got my answer for the moment. This subject offers so much info that a simple mind like mine cant take it all in over night or probably even many. I'm looking forward to hearing your story I hope its got more pictures.

Aaron - The compression sleeves are popular up here (particularly in LRBR)and all seem to shoot well. But I have never entertained the idea of one for F class so really haven't thought about it. To be quite honest it is beyond my comprehension at the moment - would have to read more on it. Certainly a weight on the end of the barrel changes the way the pulse waves act significantly so I imagine a compression would too.

Interesting idea Alan - Stabilisers like Norm has suggested have been discussed up here and a vertical one like Alans is an extension of the principle with some possible added benefits - I would avoid attaching to the rail though unless the rail is clamped down with 8mm bolts and epoxy. If you have a barrel clamp - maybe some screws in the side of that?? The stabilisers would need to be quite rigid though and the discussion up here was to hang a couple of golden balls under the "golden" tuner but thought it might raise too many eyebrows at prestigious meetings!?? We have probably pushed the jokes a bit far with the NQ big knobs already rather less throw some big balls in there as well.

After this discussion I urge everyone to have a look at two pages

1) varmintals barrel modes

http://varmintal.com/amode.htm

You will see the reflections in everyones observations. The combination is complex to think about but the reality is it is relatively easy to determine what works.

In my mind I have simplified it akin to Chris Longs OBT theory http://www.the-long-family.com/OBT_paper.htm
ie vertical movements of main barrel vibrations tend to be predictable and can be used for "compensation" load development (typical ladder). They arrive fairly consistently with respect to muzzle exit time in a "predictable and usable" manner. Then there are the "P" waves or expansion pulses (varmintals mode 4 and 8 -with a twist). these pulses can cause "scatter" nodes amongst the vertical movements we see by opening the bore diameter similar to a bad crown effect. In a large diameter straight barrel these pulses are reduced in amplitude (size) and have less effect. A small change in load however can have the projectile arriving at muzzle with an expanded bore and you will get scatter in all directions. This however can be picked up in "vertical plots" and avoided. In straight taper large diameter barrels they generally only have a minor impact.

Dave, there are two problems with hanging balls off the end of the
"Gold Member" tuner. If the balls were as big as the FNQ shooters are claiming are normal up there, the wind could cause oscilating moments which would have variable dampening effects and would likely cause the horizontal dispersal of shots as the original poster mentioned.
On a more practical side, if the stories the FNQ shooters tell are true, the life sized reproductions would put you over the weight limit and necessitate a higher front rest for clearance.