Accuracy nodes...More than one??

[dondlhmn]

Just kind of wondering about this after shooting my new 26" Krieger barreled 6.5 Creedmoor...It seems to me that I have found two accurate nodes...one with the 136L Lapua seated .010" off the lands and one with it seated .130" off the lands, with the tests in between those seeming to show that the .050 and .090 off not being all that great. I intend to single feed this rifle as it will pretty much only be used to develop the rounds and then to fire in a competition where the rules call for single feeding, so there is no real advantage to the ones seated in deeper to get the .130 off the lands. The .010 will not go through the magazine, but that is not really a factor for me, as whatever I settle on (or rather the rifle settles on) will be single feed only. So, it boils down to powder capacity, which seems, at least at this point in load development, to not be a factor as I tend to NOT load to the very maximum speeds I can get, and I am content with these 136 grain bullets heading out at 2875 fps or so, anyway. Also, pressures don't seem to be enough difference to point to one over the other....

So, ANYWAY...my question is: Have you all found there to be two pretty much equal nodes of accuracy which occur at quite widely varying seating depths? Is this common with a lot of rifles? If accuracy is related to barrel harmonics, it makes sense to me that accuracy nodes would occur at seating depths that are pretty far apart. What sort of experience have you all had with this? I'd like to hear your comments and experiences, please. If you have anything to say about this, please PM me on this site.

Thanks!

 

[Pfiddy]

Tag for answers

 

[Apothus]

In with Mtncreek, I havent seen different seating depths give me accuracy nodes, but I've only gone from 10 thou to 50 thou off the lands. Rifle likes em longer.

Now I have seen nodes appear at two different charge weights. I got a nice accuracy node at 79 grains, but it was too slow for my end goal. I ran up another few loads to get to book max, and funny thing, I found a really tight accuracy node at max of 81.8 grains. Im still shy of the speed I want, but until they make Miracle Grow for my 26" barrel, that's where I'm at.

 

[SuburbanHick]

ok thank god some one else has brought this up... ive thought about this for many hours... it would only make sense that the crown of a barrel be cut at a node (point along a standing wave where the wave has minimum amplitude). that way its not vibrating when the bullet leave... but the question is can u cut the node with out it moving?

 

[dondlhmn]

ok thank god some one else has brought this up... ive thought about this for many hours... it would only make sense that the crown of a barrel be cut at a node (point along a standing wave where the wave has minimum amplitude). that way its not vibrating when the bullet leave... but the question is can u cut the node with out it moving?

Now you have MY curiosity up.....How does one "cut" a node? Or better yet, can you rephrase your question---"but the question is can u cut the node with out it moving?" some other way?? I've heard of working on finding and using accuracy nodes by shortening the barrel (cutting it), seating the bullets either right on the lands (called "Jammed") or off some given distance which is selected basically through trial and error and testing, loading for different velocities, using different powders, using different primers, etc., etc., pretty much all of which require good old trial and error and a good bit of judgement be applied and HOPEFULLY you wind up with a brass, powder, bullet, primer, dimension combination that gives optimum accuracy.......BUT I've never heard of "cut the node" before and am wondering how that works and if it is something to add to my bag of tricks used when attempting to get the best out of a rifle.....I'm thinking that the only device that I've heard of that can "tune" the barrel accomplishes that by moving a weight installed on threads at the muzzle to find a "sweet spot" as the weight is screwed toward the action or toward the muzzle in increments. Browning marketed/installed such a device on their rifles and they called it their "BOSS" (Ballistic Optimizing Shooting System) system, but I have not really paid attention to that and don't know if they still offer it.

 

[SuburbanHick]

ooook.. here is what I ment by cutting the node... everything has harmonics.... all it refers to is where you you have vibration and no vibration in a object...

so in other words if a barrel is cut and the crown of the barrel is where the antinode is (where there is most vibration) would there be a accuracy difference as compared to the node (where there is little to no vibration).. and if there is would it be possible for a smith to recut the barrel to the node or because the face that your changing the over all length of the barrel change the location of the nodes and anti nodes

does that make sense or did I just confuse u

 

[SuburbanHick]

as for the BOSS system... I just put that under a gimmick.... but now that you mention it ... it would kinda make sense...

 

[dondlhmn]

As I consider all of this...my thoughts go this way....: Well, cutting a barrel to find the accuracy node MAY be something that can be done...no doubt it CAN be done...BUT it would be hard to predict how much to cut off and, I would think, demand that you did a lot of experimental firing to see if you were going the right direction or not...and if the experiments dictated that your barrel should be LONGER...what now? Buy a longer one? Cut MORE off of the one you have in an attempt to "chase down" the next harmonic node as the barrel gets shorter? I would think all of this "COULD" be done, but it seems highly impractical to me.....seems that a weight threaded onto the barrel and moved to find the harmonic "calm points" would be more practical. In the case of cutting the barrel to do this, you would have a barrel that was good (maybe good) with only ONE SPECIFIC cartridge/load/bullet...etc. If you used a tunable weight, it would work with the round you used in the testing phase, but could, after testing to find the "sweet spot", then be used with other rounds to suit other missions.

 

[Bubb]

There is two nodes. A high and a low. Cutting a Barrle doesn't change a high or low node, but it might make them closer. The key to accuracy is finding your node and know exactly what the velocity of it is. Your concisticy is being right at the edge of the node so temp and other factors pushing your velocity don't take you out of your accuracy node. Some times your accuracy is best with the top (faster node) or some times it's the slower. You gotta test. I live close to Ken Markel he use to own K&M reloading supply's. I've shot some of his personal guns scary accurate. All his load work is done over a chronograph shooting I to dirt no target!! Yea, you heard that right. When the numbers come in right, then he loads groups, and test velocities, and after that shots groups to test OAL to fine tune. By then it's crazy bug holes... I tell him all the ladder tests and stuff I read on hear. He just laughs.. His list of thing he has built and done are crazy. But he has forgot more about reloading then ill ever know. So I use what he tells me to do?..

 

[Rattler56]

This is where a ladder test will show you pictuler node for a load, like when I switch to a new powder I find that
in my 22-250 it will like 33 grains then go to crap till 35 grains with the same OAL and bullet weight.
Each barrel has its own harmonics and thus the search for the right node goes on.

 

[Assault116]

Didn't Berger's documentation reference something similar to the seating depth thing possibly being in multiple locations for a specific rifle for their VLD's? Something along the lines of touching on out to .150 jump IIRC. Considering the Scenar's aren't overly different in design, I'd assume they may also exhibit that same behavior.

As to the BOSS system, I once thought it was a bunch of Marketing BS until I bought a used rifle I wanted that happened to have it on the rifle. It is an Abolt Eclipse in 7mm RM which is somewhat hard to find and it was a great deal, otherwise I would have bought a standard version.

The rifle was an absolute tack driver when I got it, and I decided to fiddle with the BOSS on it just to see. Let me say this, I'm glad I wrote down the setting because when I messed with it, the groups went to absolute crap in a big hurry. All of the testing was with the same factory ammo (Federal Fusion, cause it was cheap). I was quite surprised and to this day I still kick myself in the ass for selling it to my brother.

That said, I'm not sure if it was an effect of the overall barrel length, or the position of the brake ports to the crown, or what exactly it was, all I know is it made one hell of a difference on THAT rifle.