Interesting discovery on load development.

[Clayton Halford]

Ok so I keep notes on everything I do and as I was going back over notes I noticed something.

As we know with brand new barrels they speed up after the first 150-250 rounds.

Say you do one of many methods of load development with a brand new barrel and find your node at a hypothetical 41 grains at 2750 FPS.

After 200 rounds you check your velocity and now your running 2830 FPS with the same 41 grain charge weight.

So here is my question. Are accuracy nodes based off of pressure or velocity?
Is your node 41 grains or is your node 2750? Hmmmm.

In my notes I have personally found that the powder charge is the node and not the velocity. However there is a direct correlation between pressure and velocity.

Any expert advice? What have you discovered?

 

[chromatica]

I have wondered the same thing. Here's what I have come up with:

It is the pressure impulse that sets the barrel vibrating. I would expect that the pressure profile during the first few inches of travel dominates the harmonic behavior of the barrel for the rest of time the bullet is in the barrel. I would venture to guess that the velocity part of the node is secondary and that the charge of powder largely determines the node.

 

[johnfred1965]

Check out techshooter's OBT theory. He says the pressure wave is much to slow to have an effect on the muzzle until after the bullet is long gone. The wave he is concerned with is the acoustical wave caused by the explosion of the powder running back and forth through the steel. timing the bullet to leave the muzzle when this wave have the least effect is the purpose of adjusting pressure and thus velocity. The speed of sound in steel varies little, while you can easily change velocity to make the bullet exit at the opportune moment. Just google techshooter and you can find his page.

 

[Dusty Stevens]

I can assure you that if you have your best tuned load shooting at 2750 then all of the sudden it starts running 2830 its not the same load and will act accordingly- higher impacts, wrong tune, etc

 

[INTJ]

At best, I might see 10-20 FPS increase after 150-250 rounds. Sometimes I don't notice any increase at all, and a 10-20 fps increase can be caused by a lot of things. Ideally I fine tune before each match and just go with what is best at that moment.

For a hunting rifle, I make sure the load I pick is stable enough across various conditions so small differences don't matter so much.

 

[JFrank]

I don’t use a chronograph to develop a load.
J

 

[JEFFPPC]

I don’t use a chronograph to develop a load.
J

Likewise SPJ. I let the target tell me. I check velocity out of curiosity but as they say....the proof is in the pudding. Yes, I see a correlation between velocity and accuracy or within a node, but it is all in what the target will show and REPEAT, that I make decisions on.I buy powder to last 2
or 3 years at a time so change in a lot of powder is not often reoccurring and has never been an issue for me.

 

[Bill K]

M

I don’t use a chronograph to develop a load.
J

Me either. I Find the load that is shooting the most accurately and then I check what velocity is is traveling and averaging.

 

[jepp2]

I don’t use a chronograph to develop a load.

Probably 90% of what I shoot at the range, goes over my chrono. My view is why not? I'm collecting data that I would otherwise not have. I'm shooting targets for groups, just have my chrono sitting between me and the target.

I find it very use when working up loads to determine a max load. I've already run the basis through QuickLoad with my powder burn rates adjusted for my lot of powder. Some of the pressure signs are not all that reliable. I want to know how I'm doing before I have stiff bolt lift or primer pockets loose (both indicate over max loads). And I follow the theory that velocities flatten at nodes.

A good read if you haven't read it yet: https://www.65guys.com/10-round-load-development-ladder-test/

 

[INTJ]

I don’t use a chronograph to develop a load.
J

That works okay if you can develop a load at the distance you'll be competing. However, you are missing some useful data.

The best way to evaluate the fine points of our loading practices is by seeing extreme spreads on the chronograph. That is how we tell if sorting primers makes a difference, if seating primers a certain way helps, if the method we use to sort cases helps, if the neck tension is right, etc.

Now that is not the same as tuning for the best node. Sometimes we find nodes that tolerate a wider range of velocity variation. In fact, that is our goal. However, when we are still developing our load, there is a big difference between seeing a bad group with 9 fps ES vs a bad group with 25 fps ES.

A bad group with a 9 fps ES is most definitely a bad node. A bad group with a 25 fps ES may be a bad node, but it might also be telling us we need to improve our loading methods.

I recently changed the way I was seating primers in the 6 BRA. Prior to that I was getting ES in the teens and shooting competitively enough. When I changed how I was seating primers, my ES on the 6 BRA dropped into the single digit range.

So now I am very confident that a bad group is the result of a bad node and a bigger change needs to be made. This means that I won't be chasing the the fine points of tuning but will look to bigger changes like changing the powder or bullet.

Interestingly, the 300 WSM--with more than double the case capacity, doesn't need as refined loading practices to get to single digit ES as does the 6 BRA. I wouldn't know that without use of a chronograph, especially since good groups really only show up in good conditions and the vast majority of time we are shooting in average conditions.

All this gets amplified if you have to do most of your tuning at 200 yds but must compete at 600 and 1000.

Finally, knowing our velocity is one of the best ways to see how hot we are loaded. Even with factory rifles, by the time we see an pressure signs we are past 65,000 PSI. Stan Watson, a ballistics consultant using an Oehler 43, found one brand of brass didn't show any pressure signs until 80,00 PSI, and that was in factory rifles. Without a chronograph you may have no idea your load is hot until you lost the primer pockets after three firings on your carefully prepped match cases.

So that is why I use a chronograph when developing a load.

 

[Alex Wheeler]

I have seen barrels change speed for many reasons. Sometimes it will put you out of tune other times it wont. I would say, early in a barrels life, those speed ups do tend to put you out of tune, but once that barrel settles in, you will still see velocities change from day to day, and surprisingly the center of the tune really does not seem to be linked to a certain speed. I always shoot a "window" of powder, I want to see the load go out of tune on both sides so I know the center. Always listen to the target.

 

[Metal God]

I can’t say I’ve seen your phenomenon but have over time seen Something else That is similar . I’ve seen overtime powders with very similar burn rates tend to have the same node either at the same velocity or same charge weight . It doesn’t seem to matter what bullet or weight the bullets are as long as the charge or velocity is the same .

Example

I have several 308 loads that are good at 41gr of IMR 4895 . Bullet seems to be irrelevant 150 through 175gr’s . That seems to indicate ignition pulse rather then velocity but I have other loads that as long as I hit the same relative velocity with the same bullet . The powder does not seem to matter . Now this is all very general and I can fine tune them all in some way but there does at times seem to be some happy mediums out there .

 

[C.E.Smith043]

Probably 90% of what I shoot at the range, goes over my chrono. My view is why not? I'm collecting data that I would otherwise not have. I'm shooting targets for groups, just have my chrono sitting between me and the target.

I find it very use when working up loads to determine a max load. I've already run the basis through QuickLoad with my powder burn rates adjusted for my lot of powder. Some of the pressure signs are not all that reliable. I want to know how I'm doing before I have stiff bolt lift or primer pockets loose (both indicate over max loads). And I follow the theory that velocities flatten at nodes.

A good read if you haven't read it yet: https://www.65guys.com/10-round-load-development-ladder-test/

I'm in this camp