Best accuracy/velocity node, which the other "nodes" do not equal?

If I have an accurate load and assumed node at say 2820 ft/secs, can the next node up or down be superior to that, or should they be equal. The cartridge by the way is .308/155gr , not 6 PPC or derivative of same. Another short way of phrasing this would be is there a single best accuracy node in a given barrel?

Part two of this question would be if the "nodes" are expected to be approximately 120 ft/secs apart in the 6 PPC, are they spaced similiarly in other cartridges, or does each cartridge have it's own spread or reach between "nodes?" For instance would the .308 be spaced at say 165 ft/secs?

Thank you for your considered responses.



Shot this AM, range 300 yards at the higher node! Load development is complete

We need a hamonics guy here, but I think the nodes can not be compared from one chambering to another, but rather are based on barrel masses involved, along with the loads themselves.

All things equal, I would expect the "lower nodes" to be more accurate than the "higher" nodes. Simply because the more often the barrel vibrates (the more the wave travels back and forth -- to oversimplify), the less noise is introduced. I believe this is why the PPC shooters like their 75,000 psi loads and their 20.5 inch barrels. It gets them to a lower node.

Second, the nodes are the same distance apart in barrel time, not bullet velocity (though they are, of course, highly correlated). So, the distance between node 4 and 5 would be different in fps than between 7 and 8 -- simply because the bullet is traveling at a different rate of speed.

Google "Chris Long barrel model" for better explanations. HTH, Dutch.

Although I don't believe any of this applies to me, I can help calculate.

As I understand it, you want the bullet to escape when the barrel muzzle is at peak side to side position, and thus a node in side to side velocity.

A .308 130 gr Barnes TSX bullet takes 1.055 ms to get out of a 22" barrel with 46 gr H335 48kpsi 2885 fps.


A .308 130 gr Barnes TSX bullet takes 0.937 ms to get out of a 22" barrel with 50 gr H335 63kpsi 3127 fps.

I am not sure how linear this is, but that is:
[1.055 ms - 0.937 ms]/ [2885 fps - 3127 fps] = - .000 000 4876 seconds per feet per second
Or we could think of it as -2,050,847 fps/s

Hitting the barrelled action with a hammer:
The barrelled action resonates alone at ~4 kHz. So that has nodes about .000 25 seconds apart.

Holding a rifle by the wrist and hitting the barrel with the other hand:
The bareeled action resonates with the stock at ~200 Hz. So that has nodes about .005 seconds apart.

The first set of nodes would be 513 fps apart.
The second set of nodes would be 10,267 fps apart.

I would ignore the stock.
The barrelled action alone if it had a node a 50 gr 63k psi 3127 fps, the next node down would be 41.6 gr 35602 psi, 2614 fps.

quote:

Originally posted by 308Sako:
... is there a single best accuracy node in a given barrel?

When I perform the Creighton Audette Method I look for the Harmonic Node closest to whatever the SAFE MAX happens to be in my specific rifle with those specific Components. Then I go back and Fine Tune the Load by varying the Seating Depth. Using that Method, I've so far found acceptable Hunting Accuracy with every rifle I've used, very close to a SAFE MAX.

The reason I give those specifics is because I don't remember ever intentionally backing-up to a lower Harmonic Node to see if in fact it was more accurate.

To shorten a very long story, I had a 26" Bull Barrel 308Win M700VLS that I put some Starting Loads of H380 ahead of some MatchKings just to do some Fire Forming and to get some Trigger Time. That specific Load shot better than I know I am normally capable of shooting, so I accepted it as it was. I'd "guess" there was an additional, reachable at SAFE Pressure, Harmonic Node beyond it, but I didn't look for it because this was not intended as a Hunting Load. Simply a Buddy Whuppin' Load.
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Don't have a good answer for the second part of the question. Makes my head hurt thinking about it. I would "guess" there is no Specific distance or value that can be given between Harmonic Nodes because of the variation in the Powder Burn Rates and Barrel Dimensional Variations.

Some Harmonic Nodes may be 2.5-3gr apart and some may be 5-6gr(or maybe more) apart. I'd personally be leary about backing-down on the Slow Powder Cartridges to look for additional Nodes.

However with a 308Win and H4895, you might locate 3-4 nodes. Don't know - never tried it.

Good question.

Very interesting indeed! I have been pondering this very same question.

quote:

... bullet to escape when the barrel muzzle is at peak side to side position, and thus a node in side to side velocity.

This is not actually a node. A node is the point in a wave where there is no displacement. Longitudinal waves will have nodes at the end of the barrel but transverse waves might or might not. But what is meant is that the change of direction of the muzzle is at a minimum. There is likely to be multiple wave forms present so it therefore likely that there will be more than one 'node' and that one might be 'simpler' than another and therefore more accurate. By that I mean that the minimum rate of direction change will be a combination of frequencies so the different nodes might have different combinations and hence different values.

Has anyone experimented with placing clamp on weights at different points on the barrel to try to influence the amplitude of the 'nodes'? i.e. to tune the barrel to the load rather than the load to the barrel?

My interest stems from the concept of over-barrel suppressor mountings. The added mass, the added length and the positioning of the two mounting points must surely be important in this regard. But how does one 'guess' where the best positions might be?