Rifle Nodes
BY Herschel Smith
1 week, 3 days ago
Many commonly-used terms in the shooting community aren’t widely understood or used in a consistent context, so it’s important to define what we are talking about. The technical term “node” refers to the points on a wave at which the amplitude or displacement is the smallest. In terms of a vibrating object like a rifle barrel, it’s the point at which the vibrating barrel moves the least. A rifle barrel does have nodes as it vibrates during and after a shot is fired, but when someone refers to “finding their rifle’s nodes,” they’re referring to finding the charge weight and velocity that causes the bullet to exit at or near that node or dead spot in the barrel’s movement as it vibrates back and forth.
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When I brought up the subject with Shooting Editor John B. Snow, he said that all his data had supported the idea that chasing nodes doesn’t gain you anything. He and other high-level shooters at team events will even tailor their loads to target matching velocities to simplify drop and windage calculations between shooting partners …
He goes on to discuss a number of interesting points – interesting to me, at least, including whether a 3- or 5-round group is really sufficient to show anything of value. I agree with him. It’s not.
This is true for a number of reasons. Let’s move past the implications of chaos theory. Atoms are moved by Brownian motion. Atoms bond together to form crystalline structures. Crystalline structures can slip against each other. The barrel heats as it is fired. This motion changes each time the barrel sustains a round being fired through it.
There are other effects as well. This all means that a 3-round group isn’t really relevant for anything much except inflating your ego. Now, let’s move past the issue of repeatability due to physical effects and ponder whether the action of a bullet travelling down a barrel is governed by a deterministic process or a Monte Carlo process. That is, if you could exactly measure the grains of powder charge, exactly govern the bullet weight, and exactly control the barrel temperature, each and every time a rifle is fired, would the bullet go into exactly the same hole each time? Or would the group behave as a random process in which the grouping is always described by a standard distribution?
I think about things like that.
I prefer to just do the best I can and shoot the best equipment I can find within reason. I am not a performance precision rifle competition shooter. If I was, I would probably do the things he’s talking about.
But I wouldn’t assume that a 3-shot group meant much of anything.
On April 23, 2024 at 1:09 pm, MTHead said:
Not sure exactly what it is. But in 30’06, 56grs. of IMR-4350, with a 180 gr. bullet produces accuracy in almost every gun it’s shot through.
Learn it from several gun authors, and proved it in several guns myself. Friends included. Barrel harmonics? Don’t know. But it works. So somethings going on.
On April 23, 2024 at 6:33 pm, X said:
“This all means that a 3-round group isn’t really relevant for anything much except inflating your ego.”
Like almost everything else in life, the answer is “It depends.” If it is a hunting rifle and your goal is to get consistent point of impact and small groups from a cold barrel before it heats up, a three-shot group is plenty.
On the other hand if you are shooting National Match and you need your rifle to hold 1.75 MOA or less for a 20-shot group with a hot barrel at 600 yards after you’ve already fired 30 rounds (or 60 rounds, depending on the match) in your standing and rapid stages, then yes, a three-shot group isn’t going to tell you much.
On April 23, 2024 at 9:17 pm, Herschel Smith said:
A 3-shot group still isn’t enough to fill in the standard distribution that will represent what the gun really does, and that SD won’t be the same as shown by the 3-shot group.
Guaranteed.
On April 24, 2024 at 12:13 am, The Wretched Dog said:
So, Herschel, not remembering anything substantive from my yearling (USMA sophomore) probability-statistics class, what would you recommend for a reasonable single-group size to determine load development?
I’ve loaded 50 rounds for a young huntress in five 10-round batches, increasing the powder charge by 0.3 grain for each batch of 10 to see which charge weight the rifle best groups. Charges are midrange for 6,5 Creedmoor.
Not worth the effort?
Regards,
TWD
On April 26, 2024 at 11:15 am, Pat H. Bowman said:
FWIW, Hornady did a podcast on group size a while back. Their conclusion is that 10 or 20 shot groups are needed to really give you any solid data. They also concluded that many of us spend way too much time chasing the .1 grain charge that will tighten the group perfectly.
https://www.youtube.com/watch?v=QwumAGRmz2I
That’s episode 50; right around there, they also did a few episodes on load development and followed up the group size to answer questions. I felt like they treated the subject very practically and with data to back it up. Worth the watch, IMO.
On April 26, 2024 at 5:09 pm, Lowell said:
That’s all very nice. But if your rifle, or you, can’t shoot a three shot group there is no point going further.
On April 30, 2024 at 12:10 pm, Don W Curton said:
I believe that “chasing nodes” was pretty much the entire reason for the development of the Browning B.O.S.S. system. I bought one years ago and played with it some, just not enough to see if it actually worked. It was the BAR Safari in 30-06 and for whatever reason would always throw one flyer in every 5 round group. I’d have 4 rounds grouped in a little 3/4 inch hole and a single round 2 inches away. Pissed me off to no end. Haven’t shot that gun in maybe 20 years, might be time to take it out again and see what happens.
On April 30, 2024 at 5:25 pm, Carroll said:
I believe it was expert sniper Carlos Hathcock that zeroed his weapon by shooting a single round a day while recording all related conditions. After several days, he would analyze the data and make a sight adjustment. He then verified the move by repeating the process. This method certainly ensures that on opening day you know where that first cold barrel shot is going.