How many FPS between accuracy nodes???

[HNDLDR]

Is there general rule for how far apart the accuracy nodes are or does it vary significantly?

 

[mobenzowner]

From what I know accuracy nodes are about 3% apart. This correlates to powder charge not velocity.

 

[Darkker]

It varies.
To put a number, such as X percent, you would have to have a single burning rate for each powder, not a nominal variance. Since that doesn't exist....

 

[HNDLDR]

From what I know accuracy nodes are about 3% apart. This correlates to powder charge not velocity.

Perfect. Now I know where to start looking, or more accurately whether to try to get to the next one higher or accept what I have.

 

[mobenzowner]

Perfect. Now I know where to start looking, or more accurately whether to try to get to the next one higher or accept what I have.

Also accuracy nodes are normally about 1.5% charge weight away from "scatter nodes".

 

[HNDLDR]

Thanks for the reply. I started using boron nitride and I'm trying to get my groups to settle back in.

 

[HNDLDR]

It may be a seating dept issue as much as anything. My original load was .005" into the lands. I don't know how much coating the bullet with a lubricant is going to effect things. Basically the bullet has less resistance entering the lands now.

 

[mobenzowner]

It may be a seating dept issue as much as anything. My original load was .005" into the lands. I don't know how much coating the bullet with a lubricant is going to effect things. Basically the bullet has less resistance entering the lands now.

you very well could be right. Good luck on the quest.

Kevin

 

[el matador]

I believe nodes are further apart personally. Based on Optimum Barrel Time calculations the nodes are somewhere between 8% to 11% apart, which should correlate pretty closely to velocity. So if you have a node at 2900 fps you'll probably have another one around 3150 to 3200 fps with the same powder and bullet. The reason I'm inclined to believe this is based on my load development techniques. I typically shoot from 5-6% below max to 1% over max (published data) to look for accuracy nodes. If they were 3% apart I would be finding multiple nodes within that range on some occasions, but I have not. In fact sometimes I find zero nodes and move on to a different powder altogether. I can usually find one good node within that 6-7% range, which seems to follow the idea that nodes are around 10% apart velocity-wise. Since each powder builds pressure differently that explains why the nodes may be at higher/lower velocities with each powder.

Regarding your HBN coated bullets, you should try to replicate the velocity of your accuracy load that you used with uncoated bullets. Since the coating reduces friction it also reduces pressure and velocity. You'll most likely need to bump up your powder charge a little to restore velocity to where it used to be.

 

[HNDLDR]

Regarding your HBN coated bullets, you should try to replicate the velocity of your accuracy load that you used with uncoated bullets. Since the coating reduces friction it also reduces pressure and velocity. You'll most likely need to bump up your powder charge a little to restore velocity to where it used to be.

First of all thank you for your insight. My experience with the BN hasn't followed the rules so far. My load was an average "In my rifle only" pressure with barely any flattening of the primer. The BN almost eliminated any flattening of the primer so it did reduce the pressure. Where it broke the rules is it gained about 40FPS instead of losing velocity I was able to easily gain another 100 FPS over my original load with no pressure signs butt the groups opened up.
That's what got me wondering if I should try to search out another accuracy node or reduce my powder charge to get back to the original velocity.

Rifle=LH Browning X Bolt 25-06
Case=Norma
Bullet=Berger 115 VLD seated .005 into Lands
Powder=52 GRS IMR 4831
Primer=WLR
Velocity=3030 FPS

This is my original load. Four shot groups at 100 yards were consistently between .3" and .5".
Once the BN settled in. "Approx 30 shots" groups ran about .75" to 1.0" with original powder charge.
Velocity also took a bit to settle in at around 3070 FPS.
This is a Hunting rifle and my only interest in the BN is a consistent first shot, out of cold fouled barrel, as in a hunting situation. I have verified, and am happy with, the BN's ability to achieve this.

 

[el matador]

Well I'm no expert with the HBN but I really like it so far. I've got a load in my 270 WSM where the accuracy node is right at max pressure with uncoated bullets. Using the HBN I can easily get the velocity I need without any pressure signs.

Interesting that you're getting higher velocity with the same powder charge. Might have to do with being right on the lands, I don't know. I still think you need to get back to 3030 fps for best accuracy since the next higher node will probably be out of reach. Let us know how it works out.

 

[HNDLDR]

I still think you need to get back to 3030 fps for best accuracy since the next higher node will probably be out of reach. Let us know how it works out.

I agree I don't think I will make it to the next one. Which is fine. I was happy where I was before.