Any thoughts on No1 Mk3 harmonics?

[RJW NZ]

I'm sitting here playing with the insides of my Fultons no1mk3 and wondering if the three internal springs are situated exactly on nodal points, or not ...
So I've been looking all over for a diagram of the harmonic vibration points of nodes/antinodes for the stock smle barrel but to no avail.
I have the James Sweets diagram of the H barrel nodes and measurements but there's no notation how close that is to the stock barrel.

I found this online;
"OK, back to harmonics ... if one hasn't tried this method to determine the barrel null point, give it a try because it does work

On the top flat of an octagonal barrel, sprinkle talcum powder the length of your barrel. Holding the rifle level, shoot it off hand. Then look at the talcum powder. It will be figured like this in waves:
>>>>>>>>>>>>>>>>>>>>>> <<<<<<<<<<<<<<<<<<<
At the point where the 'waves' reverse that's the null point of the barrel for a given reload. Then shoot a few bench rest groups for verification"

It sounds a bit interesting, can one really do this with bits of wire as I read someplace? How, whats the method so I could try it?

Should the bullet be leaving on a node or antinode or middle?
Does one add bedding on the node or antinode, or something else entirely?

If the positive compensation were such a good thing on No4's then why wouldn't we all strive to create that effect on other rifles/enfields?

Thanks, this has long been a question and finally getting around to it.

Information

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[jmoore]

Ideally the muzzle should be at a node. Bedding as well, or it'll make things worse. The problem for the old timers was that it was exceedingly difficult to predict just exactly where those calm or "dead" points were going to be without experimentation in the real world. But even w/ the computer modelling available now, it's not so easy if the barrel isn't completely free floating and has no "junk" attached to it.

The wire method can work if you build some sort of fixture to hold everything in place.

[Peter Laidler]

What also plays an important part is that because the barrel is a simple bell (hang a bare uncluttered one up and tap it) that vibrates, the steel mix/content will also play an important part in the way it acts too. This effectively makes every barrel (or every steel batch) act very slightly different. What we aim for in military life is a good compromise. Dynamics is one of the subjects that's difficult to simplify so those tutors are always sought after in the physics labs..................

[breakeyp]

In the car business, we determined a part's natural frequency and several other modes by using an accelerameter and a frequency analyizer. Fix the accelerameter on the part with beeswax and bang it with a rubber mallet. The FA gives you a nice graph on a screen or paper print out The last one I saw ten years ago was even suitcase portable. I imagine you can a set up for five or six grand. Just a thought I you really want to go to the effort.

[Thunderbox]

I'm sitting here playing with the insides of my Fultons no1mk3 and wondering if the three internal springs are situated exactly on nodal points, or not ...

Looking back through the Text Book of Small Arms - which has hundreds of pages of ballistics analysis - and other contemporary sources, its clear they fired of millions of rounds just in testing and development. IIRC (brain fade) one book even has spark photographs (early high-speed photography) of barrel behaviour during the firing sequence. I guess they did a pretty good job of identifying barrel harmonic points through inspired trial-and-error. Its interesting that some No1 rifles can be so sensitive to tiny adjustments of the inner band screw & spring - clearly the inner band does indeed sit on crucial location on the barrel.

[Peter Laidler]

I appreciate that it's a bit nerdish but this thread is VERY interesting. To me and the rest of the engineers it's a bit like the material failure thread of a year or so ago. Harmonics is one of those uni physics subjects that you try to stay interested in and absorb JUST enough to pass that phase exam.......... phew. But later on you realise just what a big part it plays. Metal fatigue and frequencies for example.

Sorry for rambling on..................

[breakeyp]

Peter, the boffins I had to deal with were 100% accurate on telling you what happened but were totally useless in predicting or solving problems. Condolences.--it is like dandruff shampoo---alot of people fool with it and seem to derive great pleasure from fiddling with it.

[jmoore]

Airframe and aicraft engine parts usual nemesis is vibration induced fatigue. Very mature industry, but we still get "surprises" from time to time. Usually when anexisting design is "upgraded" for more power or carrying capacity. What seemed to be a "no worries" component suddenly becomes a maintenance nightmare. All due to vibration.

It's hard to predict and hard to measure at times, as merely getting to the point where you can observe and measure it means anough changes have been made to the system that the harmonics are upset. (I.e. removing barrel bands and handguards to "watch" the barrel.) That's why most pure accuracy rigs (benchrest rifles) have free floated barrels- less interactions to worry about.

[Peter Laidler]

I talk about the big killer of L7 FN MAG GPMG's being vibration and the importance of 'balancing' the gun but it washes over them. I wish there was some simple device that I could use during a lesson that would illustrate. I do use the ringing barrel to illustrate certain parts of the train but it's the 'keeping it simple' part of any such lesson that is difficult. Great thread

[Bruce_in_Oz]

Ah, the MAG-58!

It is quite satisfying to make one "sing". Not so soothing is the near spilling of a hard-earned coffee on the range, when assailed by a sound like canvas being torn very loudly.

Some folk seem to equate "fast" with "good" and crank the regulator all the way from "economy" to FUN!"

The thought of washed-out throats, hammered belville washers and loose rivets is disconcerting.