Good Vibrations

[williada]

I want to throw in a few concepts with regard to good vibrations that enable you to refine your nodal tune and they are a pre-requisite to compensation tuning if you use that to. I want to consider the lighter actions which historically I had more experience with.

The major problem we had to rectify in the past was the flex in the action while it supported the barrel. I keep coming back to the load area of that 6 o’clock lug in a flexed action. While it may not take on wear characteristics you can see it bears most of the tension. Because of this, the vibration in the gear is commenced below the centreline of the bore. A better vibration pattern that is more readily tunable is one that is centralised with the bore. An uneven vibration pattern also finds itself being reflected through the threads of the barrel/action mate into the barrel sine wave and we know that all threads along the shank pull with increasing force towards the shoulder. We even know that changing headspace tension by way of crush fits or brass shoulder contact or brass hardness can affect the relationship of the threads and recoil patterns therefore group size. (Think about why some people are meticulous about shoulder bump and annealing.) Many shooters do not realize it is only the sides of the threads that pull things together. So those tight feeling threads, that bind on the tops and bottoms which some think is good, destroy accuracy and they move as things heat up. This is why top machinists like Jack Harby would polish the threads. A joint that gradually firms up when you screw the parts together is a good one, so don’t worry if it feels a bit loose to begin with. A thread should be cut to strict conventions. It is the flush fitting faces of the barrel and action that stop the wobble and allow the good vibrations to flow through. There are many problems associated with poor jointing due to misalignments of action face and barrel shoulder or threads not cut concentrically with the bore and these are compounded when simple bedding is not regulated properly and the action is flexed. This includes takedown screws that are misaligned and not perpendicular to the action in drawing it down.

How do I know this? Harold Ryan, working at Monash Uni and Jack Harby (who married my mother) who was the head machinist /tool maker for the Melbourne Uni Metallurgy Department made gauges to measure the flex to ensure that the bedding of their rifles presented everything in alignment and things were assembled properly. I have inherited Harold’s rifle and Jack’s equipment. I still have a couple of Harold’s long internal barrel micrometers that enable me to measure any part of a land or a groove in a .30 cal barrel that he made and a few were lucky to purchase from him.

A little history.

When I was eighteen they captured my imagination, as did Brian Titcombe a mines engineer and Jim Alley a former motorbike race rider like Jack. We were all club members. It was indeed an honour to be invited by the old guys to play pool at Harold’s on Thursday nights to discuss team tactics and gear. In those days we fielded 3 pennant teams at the club at it was big deal. The Victorian State Teams Championship was an even bigger deal. Both Jimmy (a Queens winner) and Brian were in the Australian Fullbore Team and in those days closer to a 1000 shooters could attend a Queens. And if you think back to when Percy started there was probably 30,000 shooting in Victoria at the turn of the 20th century. So getting a badge in any Queens was quite an achievement let alone winning compared to today. All these blokes knew how to regulate their gear and they were a little more sophisticated than most but they were inclusive and always wanted to do better.

Essentially, Harold and Jack measured from the re-enforce to the tang with a dial gauge on an arm. When the action screws were drawn up they would observe the flex. In later years, the secret of their large bedding area was to place supports under the barrel to allow the action to float without tension while the Devcon set (bedding compound), without screws pulling stuff into place. They would only let the rear face of the recoil plate touch on their finished jobs. In those days, actions did not have much support because a lot had the takedown screw pulled through the recoil plate. Or in the case of M17’s there was bugger all in front of the front takedown screw. They prevented flex in the action by placing a small bed under the barrel at the re-enforce. They were the first to place further screws rearward in the action of Omarks and later Muzgraves to spread the load to stop action flexing and to take pressure off the front of the bed. They finally did away with the recoil plate screws, but used tang, middle and one about an inch an one eighth from the rear of the recoil plate.

Because actions were not pillar bedded, they did not draw the front screw down too tight to crush the wood. A case in point, bragging not intended only the learning experience. In my first state team, my good gear died after selection. Bill Elmslie presented me with an Omark bedded on the wood. Percy had checked it and scraped the bedded area including the barrel re-enforce area checking it for proper contact area with powdered charcoal. Not graphite or oil. The charcoal was dry and would blow off. Think why he did not use graphite or oil. Charcoal did not allow the action to slip, a bit like rosin. Then to my amazement Bill said the front screw has about 16 inch lbs and the rear 8 inch lbs. I shot the bloody thing and got a 50.10 with L2A2 144grn military issue at 800 and 50.6 at 900 (with irons in those days) in a moderate southerly at Williamstown and was written up in the Sporting Globe as a feat rarely achieved, (the 10 centres) by old Bob Nixon. He was used to .303’s I think. I was told to release the tension at the end of the day and nip the screws up before use. That was about 40 years ago. I learned a lot that day and subsequently have never used tension more than wood density which on walnut is about 33 inch pounds.

Those old blokes didn’t need a torque wrench, I did, they worked in 1/16’s and quarter turns and knew what the tension was by feel. They then held the rifle up in the vertical, tapped the butt on the ground a couple of times, then still holding the rifle in the vertical at the front takedown screw position, tapped the muzzle and then the butt for resonance and adjusted screw tension a 1/16 th of a turn until they got the right pitch they wanted. Like tuning a guitar. You can’t tell me that they did not understand vibration and group size and drew on experiences 40 years before my time even then. Those guys even dampened barrel vibration with chopped up cork on their .303’s. They could do that in a full wood. If they suspected a poor barrel action joint, they used cardboard as a temporary fix under the re-enforce or muzzle bed. Their muzzles normally had about 9 lbs upward lift. But if you think about it a slight upward lift even on the Omark of the barrel would pretension the threads and help if there was a sloppy fit and could assist accuracy.

These days on a pillar bed or aluminium bed I go 55 inch pound, but I still tap the muzzle and butt for pitch on a free floating barrel.

Its not surprising a glue job not only dampens vibrations, but it holds the action in a relatively stress free state without tensioning that 6 o’clock lug area. Likewise a barrel block allows the action to float without tension too and you can compensation and nodal tune by moving the barrel fore and aft in the block.

Modern actions like RPA’s, Barnards etc. spread that bedding load and there is no need to worry to much about flex using a normal bed or an aluminium Vee block. Anyway, my wife is going to kill me if I don’t get the housework done. David.

[Razer]

David,
I have been shooting since I was 12 years old and that is over 60 years ago.
I read just about everything that I can to improve my knowledge, in particular, about ballistics and obtaining accuracy, most not always written in an understandable way .
There are answers, just in this last post of yours, that I have been unable to find no matter where I previously looked.

I feel that this forum has just uncovered a gold mine of information through your contributions. A sincere thank you for your time and input, it is most appreciated.

Having said that, I have a single shot Mauser Mark X (Yugoslavian) in my gun safe. It is pillar bedded on Arma-grout on top of an aluminium insert. When I first bought this rifle it had 2 pads of what looked like toffee. One just behind the recoil lug and the other centred on the middle take down screw. This material was sort of soft, so, eventually it flattened out and this flat based action has since been re-bedded so that it sits on grout at the same points.
It has never been as good since the original material deteriorated.
I even tried using gasket rubber cut to the same size as the original pads but to no avail.
Obviously his toffee coloured material was used to dampen vibrations, but just what it was I have no idea and the gunsmith as long since past on.
Would you know what it might be, and, was this an old gunsmiths method used for flat based actions?
Is there a modern substitute?
Any suggestions on how to bed these actions to get those 'good vibrations'?
Thanking you in anticipation.
Ray.

[RonM]

David,
Outstanding! Thank you for sharing. I have not seen much of this information before and it has added greatly to my learning of the many whys and hows of target rifle accuracy. There is much to be done in looking to my rifles (Omark.308 and Barnard .308) for improved accuracy and consistency, not just the attention to ammunition preparation and shooting technique. I look forward to many more of your contributions to this great forum.
Sincere Regards,
Ron

[williada]

Ray, would you believe I have given a Mark x to my son and it was originally Ed H's who no longer shoots and he brought it down from NSW when he came to live in Victoria and it had that honey coloured stuff and guess what, it was high strength Araldite. Some of the blokes used to mix a few iron filings with it; and I once owned a number 4 and used it as bedding material because the forend is supposed to flex a little bit behind the draws and promotes that compensation and it was excellent under the front takedown screw which sits on a pillar anyway. Jack Harby borrowed it and took it to England a did well with it with a Shultz for the longs. It was hard to extract it from him it shot so well. Its still a good barrel liner in an aluminium block and it parts in the deep freeze. Nick S always had a thin gasket in his barrel block to dampen vibration. Araldite does the same thing. Don't worry it has tremendous strength.

It is likely to be Araldite because it does soften. Acraglass was also a toffee colour in those days and depending on the mixture could soften but that had a smooth texture to it when you carved it and was not brittle like so many other compounds we have used. I don't like Armourgrout, it is just too hard. Walnut and blackwood and I would venture to say Queensland Maple a favourite of Percy's are the right density for the harmonics. Percy was famous for using Queensland Maple in his 3 piece laminated stocks up the guts with blackwood stringers down the outside. It was vibration absorbing in the middle with Maple and stiffen with blackwood for a reason. Another trick he used was a candle if he was bedding on the wood to harden a small insert, particularly with number 4's and people thought he was smoking it to see where to make the next cut. He used to kill himself laughing with that one.

Anyway, enough story telling. If it is re-bed, try to make sure the action does not bend and with those Mausers you have to replace the spring on the pin regularly. Make sure the takedown screws don't touch anything except on their way through the stock except at the bottom. Hope this helps Ray. David.

[Razer]

Hope it helps? That is a big 'yes'.
It explains most of the problems I have been scratching my head over for 10 years.
Thank you David for that information, gives me the answers to several areas that I need to revisit with this rifle.
The pillars are aluminium tube and when I re-bedded this action some years ago I allowed the grout to extrude into them with the action screws lightly tensioned.
First job is to clean out pillars as I obviously have the whole box and dice too rigid.
Second will to scrape the bedding down so that the only contact points are where the tang and the original pads were.
Third is too make up some high strength Araldite pads and place them on those points.
I used to tension the main screws at 55 inch pounds and the tang at 50 so as to avoid distortion of the action.
I now run 2 Barnards so this once 'No 1' rifle may get an airing again as accuracy wise it was excellent.
All I need now is some time to do it.
Thank you, too much information is being lost that is still relevant, in spite of all the modern technology, designs, metallurgy, etc.
Another question! Cylindrical actions are bedded part way up the sides, so, is clearance needed at the side of the Mauser ?because, if so, what stops the action from 'squirming'(?). I was tempted to re-bed this action with a flush fit on the sides to keep it centred.
Ray.

[williada]

Ray, take the bed up the sides at least 1 1/4" behind the front takedown screw and on the tang. By all means you can bed the full length with Araldyte which has that give. You could do a full length glue job with it, if you don't use release agent and want a permanent set up. You will have to rely on a big deep freeze to release it in that case. If you use Devcon etc, I would relieve the rear surface on the tang.

If you do use release agent like floor wax, you must never twist the barrel and action trying to part them. It will damage the bed. I use a mandrel that extends from the bolt race and the barrel to suspend things. Coat the mandrel with electrical tape to protect things. Then I have a "c" section tool made out of pipe that covers the action for its full length and rests on two wooden strips between it and the stock to prevent damage to the stock. Next give the "c" section a sharp wrap on top so that the barrelled action parts in the vertical.

I would say, that once the wood is crushed by a high tension it will always be subject to humidity changes. Try and seal it and run 30 inch pound on the front and 15 on the tang if you remove pillars on a Mauser. I would leave the pillars in place and run with 45 inch pound. Eric T used that on his Muzzie which was a beefed up Mauser by design and so was an M17 or P 14 depending whether you lived in the USA or Britain. You can always take the pillars out, but I reckon they add a bit of support the stock once they are in and if fitted correctly there should not be any squirming.

I must add that sometimes that thin gasket paper on top of the pillars will assist vibration control and the wall thickness of the pillars are not too thin and their outside diameter is bonded to the woodwork.