Question about velocity nodes

[RaySendero]

hounddawg,

I know its been a while. I am interested in your post.
Was letting other have a chance 1st,
but since none - Here's me:

Let me rephrase your comment from

"this caliber and this bullet likes this powder"

to

"this cartridge and this bullet likes this powder"

Is that what you meant?

 

[jugornot]

Since this was dug up again, here's my last results from my trip to the range.

Series 1 Shots: 5
Min 2769 Max 2811
Avg 2783 S-D 17.2
ES 42

Series Shot Speed
1 1 2811 ft/s
1 2 2770 ft/s
1 3 2788 ft/s
1 4 2778 ft/s
1 5 2769 ft/s
---- ---- ---- ----
Series 2 Shots: 5
Min 2773 Max 2797
Avg 2785 S-D 8.8
ES 24

Series Shot Speed
2 1 2797 ft/s
2 2 2782 ft/s
2 3 2787 ft/s
2 4 2773 ft/s
2 5 2789 ft/s
---- ---- ---- ----
Series 3 Shots: 5
Min 2769 Max 2789
Avg 2780 S-D 7.3
ES 20

Series Shot Speed
3 1 2769 ft/s
3 2 2780 ft/s
3 3 2781 ft/s
3 4 2784 ft/s
3 5 2789 ft/s
---- ---- ---- ----
Series 4 Shots: 5
Min 2771 Max 2789
Avg 2778 S-D 7.0
ES 18

Series Shot Speed
4 1 2789 ft/s
4 2 2773 ft/s
4 3 2771 ft/s
4 4 2780 ft/s
4 5 2778 ft/s
---- ---- ---- ----
Series 5 Shots: 5
Min 2758 Max 2792
Avg 2776 S-D 13.0
ES 34

Series Shot Speed
5 1 2780 ft/s
5 2 2792 ft/s
5 3 2769 ft/s
5 4 2758 ft/s
5 5 2782 ft/s
---- ---- ---- ----


seat group
0 0.6
0.01 0.74
0.02 0.51
0.03 0.33
0.04 0.75
avg 0.586

This test was for playing with seating depth from on the lands to .040 off the lands. Some other notes the first shot was from a cold barrel and if thrown out brings the SD down. Also the shots were pretty quick and the barrel was pretty warm by the end. It seems to indicate the velocity fell as the barrel heated. Is this consistent with others experience? By the way the groups are measured c-to-c. I will also have to start using fouler shots and give more time for barrel cooling.

 

[jugornot]

Ray, the author was saying that he had tried 8 different powders and they all settled on the same velocity/accuracy nodes. More interestingly he inferred that the velocity nodes were also accuracy nodes. At least that's what I got.

Bill

P.S. The text does not convey this as accurately as the video. Watch the whole video but the interesting part starts at about the 16:00 minute mark and last about a minute. 6.5 Guys

 

[RaySendero]

jugornot wrote:
Ray, the author was saying that he had tried 8 different powders and they all settled on the same velocity/accuracy nodes. More interestingly he inferred that the velocity nodes were also accuracy nodes. At least that's what I got.

Yes.
But I understood that was for a Cartridge not a Caliber.

 

[hounddawg]

@RaySendaro

That .223 barrel got moved from the MDT chassis I had it in to a Choate synthetic, between that and the cold/snow I have only been able to get it to the range once and that was used for tweaking in the action screw torque values. Tomorrows range session will be breaking in a new barrel on another rifle but maybe later this week I will do some more experimenting with the .223. If not this week then next week for sure.

 

[Unclenick]

I have my doubts about the velocity node concept. Barrel time nodes, yes, but the same velocity produced by different powders will have different barrel times. Perhaps if you don't stray too far with burn rates the barrel times will come close enough for it to work out.

 

[hounddawg]

You are probably right UncleNick, but I like to mess around with this stuff. I have a couple of good Varget velocity nodes for this barrel in the MDT stock so if they hold true for the Choate all I have to do is try and duplicate that velocity with 4895 and H335. I will be all ate up with this new tactical I built this week and probably next so it will take a bit. I will pin a 3 x 5 to my bench so I don't forget.

 

[Yosemite Steve]

My gunsmith put this in a way that makes perfect sense:
"When a gun is fired it rings in an oval pattern. The longer the oval the better. Depending on the speed of the bullet, it will exit the barrel at some point in that pattern. A node is where the bullet exits the barrel at one end or the other of the oval. Bullet seating depth also effects this and the amount of neck tension."
I
When he told me this all of the node concepts made perfect sense. Call it a velocity node or a barrel time node or just a node. What I believe is that there is a certain note that a barrel will naturally play. If you find a charge that compliments that harmonic I think it will make the oval longer and skinnier. Then make the bullet exit at one end or the other. It's all hypothetical but to me it makes sense.

Today at the range I found seating depth nodes at various depths. The powder charges remained the same. Using the Berger method with only four depths seemed like a wide range but I tried it and got my best groups touching the lands and .090" off the lands. The difference in average velocity was 10 fps. with the highest deviation being 8 fps. and lowest being 4 fps. That was using my H450 and 180SST bullets.

My 20 seating depth method yielded much more information. I found 4 sweet spots. It took 5 hours!
This round was IMR4064 and 150SPFB bullets.
5 round groups all the same starting powder charge:
lands - 2.5 MOA 2576 fps
.002 off 1.25 MOA 2598 fps
.004 off 1.5 MOA 2603 fps
.006 off 1.25 MOA 2601 fps
.008 off 1.0 MOA 2591 fps
.010 off .75 MOA 2585 fps
.015 off 1.75 MOA 2582 fps
.020 off .5 MOA 2579 fps
.030 off .5 MOA 2569 fps
.040 off .5 MOA 2558 fps
.050 off 4 MOA 2547 fps
.060 off 2.5 MOA 2530 fps
.070 off .5 MOA 2535 fps
.080 off 1.5 MOA 2531 fps
.090 off 1.5 MOA 2516 fps
.110 off 3 MOA 2519 fps
.130 off 2 MOA 2528 fps
.150 off 2 MOA 2529 fps
.170 off 2 MOA 2519 fps
.190 off .5 MOA 2508 fps

At .006 off the lands the velocity peaked. I then saw first hand how the velocity drops due to gasses leaking around the bullet as they were seated further away from the lands. Right at the end where I would not have expected to see it I got another .5 MOA.

I'm not sure what I want to do next. I was impressed with my new case preparations as my biggest deviation for the day was 11.7 fps and my smallest was .7 fps. THe average was 4.7 fps. Nosler brass rocks!

I stand corrected on many levels.

 

[hounddawg]

That's a lot of bullets and barrel wear lol. I just shoot em at manufacturers suggested length when doing a powder load workup. Leave them at that if they are SMKS and if they are Noslers move them up to .010. Pretty much works every time for me

 

[Yosemite Steve]

I keep reading articles that say that the best place for a bullet to exit is in the middle of the vibration of the barrel. Does that not create a more challenging and smaller "node" to work with? Would it not be better to let go of the barrel at the top or bottom of the vibration such that tiny variations in velocity would still put those bullets in closer proximity to each other?

That's a lot of bullets and barrel wear lol

It was a valuable endeavor that had to be done. Life is short and I have much to learn.

 

[Stats Shooter]

I have done workup where I started at SAAMI and moved all the way into the lands. I have done workups where I started at the lands and worked back to SAAMI.

What I do these days is call the bullet maker (if I have never worked with that bullet before), ask them, and work a little in front of, and behind what they say.

For instance: Hornady recommends their ELD -M to be 0.02" off the lands. I spoke with the tech for about 30 min on the phone....and I am from Nebraska , been to their plant many times to buy cheap plinking factory seconds and talked with them.
Anyway, I start at 0.020, I move back to 0.030ish in 0.003 increments and up to 0.010. So far in .308, .270, .300wm, and .223 their recommendation has worked very well.

I had to switch from 200 gr accubond in my .300wm to 200 gr partitions because the AB was too long for my Model 70 magazine and the best accuracy required me to single shot it. The partition is almost 0.15" shorter so I was able to move the bearing surface closer to the rifling. ...and it's a hunting rifle so it needs to feed from the mag.

However, with sierra match kings I have found seating depth not to help/hurt much (within reason).

Some bullets seem to have a jump that works best at all powder charges. Some like the match king really doesn't. For this reason, I tend to choose tangent ogive bullets because I load for too many rifles and just don't want to wear a barrel out with bi-variate pairwise testing.

So I subscribe to the Chris long/uncle Nick barrel time theory, and use tangent ogive bullets.

I may lose some BC against the VLD's, but I don't have to chase lands as much, and load development is much faster.

 

[jugornot]

Funny but group size took a significant dive at .030 off the lands. Amazing that seating depth could make from .5 to 3 MOA difference. I don't know what node or not is affecting accuracy/velocity,, but evidence does appear to bear it out. My next range day will be groups with my powder weight and .030" off the lands. I do know if I aggregate all 25 shots from my last range day it would have been a group .090" high and .058" wide. That is very satisfying to me. All that is c to c. Do you measure groups c to c or extreme spread?

 

[Yosemite Steve]

Center to center.

 

[Unclenick]

I agree with Jugornot that it looks like a seating depth sweet spot at 0.030" ±0.010" may be real because of the consistency over 15 shots in that range. Overlaying those three groups would confirm or deny it. Similarly, the wide groups between 0.110" and 0.170" (a bad spot) look like a consistent bad spot (high rate of muzzle motion). The rest of the points look like they are showing us the random size variation expected from five-round groups, for which 95% confidence is a range of about 240% variation in size.

The next step would be to run a load ladder at 0.030" and see where the middle of the best charge weight for that seating depth is.


Steve,

The muzzle motion patterns are all muzzle deflections that come from bending of the barrel at a node that is usually a quarter to a third of the way back from the muzzle. The timing of it is determined by when the recoil peaks, how much pressure behind the bullet distorts or tries to stiffen the barrel, and the shape of the barrel and its material. In principle, the slower the powder burn rate is, the longer the barrel time associated with a given velocity will be. This is because the acceleration of the bullet is not uniform down the barrel. If it were (pressure constant down the whole barrel length) or if all pressure curves had the same shape, then you could use velocity as a surrogate for barrel time. But for a given muzzle velocity, a fast powder will have a high peak and modest muzzle pressure, while a slow powder will have a lower peak and higher muzzle pressure. This means the slower powder provided less of the bullet's total acceleration at the peak and more of it later in its trip down the tube. That draws out the barrel time, so the bullet will exit at a different point in the muzzle swing. That is what a barrel tuner corrects, changing the timing of the muzzle swing to a slower changing phase to match the timing of the bullet exit.

 

[hounddawg]

Biggest problem with 5 shot groups is you never know how much is random and how much is the load. I have fell back to doing initial 3 shot groups if it the load looks promising then loading another 5 or ten rounds to see if it continues to group or spread out.

It helps if you can prepare the cases at home and do the actual powder and bullet loading at the range. Nothing fancy required and even a Lee hand press for seating and a simple box to protect the scale from wind will do the trick.

A few months back I discovered the wonderful world of mean radius and circular error probability. It gives a much clearer picture of a group/load than simple extreme spread analysis. There is an inexpensive piece of software called Ontarget that will do all the calculations for you if you scan or download a picture of the target into it.

 

[jugornot]

I do 3 shot groups for powder also. But it is because I can not get those single digit ES That Scott Satterlee gets. So I do some averaging that seems to be helping me get some better specs with my reloading. I will settle for single digit SDs for now if I can get them consistently. I guess it doesn't matter how you achieve accuracy as long as you use good methodology to get there. One thing that has been added to my process. I now lube the bullets. Anyone else a bullet luber for precision rounds? Have fun everyone.

 

[Unclenick]

Jugornot,

How do you seat your primers? They need to be compressed a little into the cup (2-4 thousandths) for best consistency.

"There is some debate about how deeply primers should be seated. I don’t pretend to have all the answers about this, but I have experimented with seating primers to different depths and seeing what happens on the chronograph and target paper, and so far I’ve obtained my best results seating them hard, pushing them in past the point where the anvil can be felt hitting the bottom of the pocket. Doing this, I can almost always get velocity standard deviations of less than 10 feet per second, even with magnum cartridges and long-bodied standards on the ’06 case, and I haven’t been able to accomplish that seating primers to lesser depths."

Dan Hackett
Precision Shooting Reloading Guide, Precision Shooting Inc., Pub. (R.I.P.), Manchester, CT, 1995, p. 271.​

The other thing, if your loads are not compressed, is to try the powder either over the bullet or over the primer for every shot. In .30-06 with a low 82% case fill, I've measured 80 fps difference in velocity of the old National Match ammo between those two powder positions.

 

[Yosemite Steve]

The other thing, if your loads are not compressed, is to try the powder either over the bullet or over the primer for every shot. In .30-06 with a low 82% case fill, I've measured 80 fps difference in velocity of the old National Match ammo between those two powder positions.

How do you position the powder over the bullet? I have heard of using filler between the bullet and powder but how does one keep the powder at the bullet end without interrupting ignition?

 

[jugornot]

It just so happens that my 308 is very close to a compressed load. I use the shake test and can not hear any powder moving. Also my ammo is stored bullet up. My rifle is a single shot and I load very carefully pushing the cartridge to about 1" before its seated in the chamber and closing the bolt fairly softly. All this keeps any powder voids away from the primer. As far as the primers I took your suggestion and measured the pocket and the primer and aim for .003" crush when seating. I no longer measure every round since I developed a feel for the seating operation. But I still spot check every 5 to 10 shells. At this point I would like to thank Unclenick and Hounddawg for all their input. I feel they have helped me immensely in my quest for accurate ammo. I'm learning it is not one big thing but lots of little things that add together for good ammo. For the hunter, plinker or casual shooter. it is all a waste of time, but my 308 which started at over 1" with Black Hills Ammo, is now getting near .5" groups at 100 yards.