Are ADI Starting and Max Loads Linear?

[jezzab]

Im starting my reloading journey and im trying to simulate a Hornaday 139gr Whitetail 7mm-08 round using ADI AR2206H. Looking at the ADI data, it shows your Starting load and the Max load, is this data linear (or logarithmic)? So if I wanna hit 2840fps as per the box, I would be (based on the info) _around_ 42.15gr? Based on my calculated linear chart of the low and high attached.

Yeah yeah I know I will need to work up and test/chrono, im just curious how this matches others. I've read some people just "pick the middle" of Starting and Max, but they dont mention if their velocity matched etc.

Jez

[bladeracer]

Im starting my reloading journey and im trying to simulate a Hornaday 139gr Whitetail 7mm-08 round using ADI AR2206H. Looking at the ADI data, it shows your Starting load and the Max load, is this data linear (or logarithmic)? So if I wanna hit 2840fps as per the box, I would be (based on the info) _around_ 42.15gr? Based on my calculated linear chart of the low and high attached.

Yeah yeah I know I will need to work up and test/chrono, im just curious how this matches others. I've read some people just "pick the middle" of Starting and Max, but they dont mention if their velocity matched etc.

Jez

No, pressure builds additionally as you reduce case volume by adding powder. Work with a chronograph if you need to replicate an existing load, you will have to chronograph the factory load in the rifle first to know what velocity it makes. And keep the brass the same, ie - all fire-formed or all full-length-sized.

[jezzab]

Ok, so its logarithmic. You could never "assume" that (Start load + Max Load )/2 (ie half the both/middle) will be half the velocity?

[jezzab]

Sorry, im not trying to be rude or anything like that, im just genuinely curious. I want to understand it and I appreciate you replying with your info so I can learn more and visualise/understand

Anyway, Ill just work up a load from the starting load until I hit my selected velocity and see if anything matches up data wise

Thanks

[bladeracer]

Ok, so its logarithmic. You could never "assume" that (Start load + Max Load )/2 (ie half the both/middle) will be half the velocity?

I would say no. If you increase from say 20gn to 21gn you'll see an increase in pressure and velocity, if you then increase to 22gn you will see an increase that is greater due to the decreased volume. As you approach the pressure limits (where you start seeing signs of excessive pressure), say 25gn, just a tenth of grain more might push you into high pressures. I don't load anything as hot as factory ammo, except the .204, but it doesn't give me any pressure signs and still has good case life.

Don't get too caught up in chasing velocities. The difference between a starting load and a maximum load might be 150fps or less, which might equate to you being maybe 50m closer to the target, or less, for the same terminal velocity.

[bladeracer]

Sorry, im not trying to be rude or anything like that, im just genuinely curious. I want to understand it and I appreciate you replying with your info so I can learn more and visualise/understand

Anyway, Ill just work up a load from the starting load until I hit my selected velocity and see if anything matches up data wise

Thanks

You can do that, I've done it numerous times but rarely keep velocity data in the logs. I generally do load development for group size, once I decide on the charge I want based on its ability to group then I'll shoot them over the chrono to get the velocity. I rarely care what the actual velocity is but I want to know it so I can calculate the trajectory. If you load ten rounds of each charge, at intervals of say 5%, and record every shot, calculate the averages, and plot them you may see a distinct curve. Or you may not depending on how good your data points are. If the loads are within a few fps of extreme spread I would think the data would be usable.

[jezzab]

That totally makes sense. Thanks!

[on_one_wheel]

Sorry, im not trying to be rude or anything like that, im just genuinely curious. I want to understand it and I appreciate you replying with your info so I can learn more and visualise/understand

Anyway, Ill just work up a load from the starting load until I hit my selected velocity and see if anything matches up data wise

Thanks

You can do that, I've done it numerous times but rarely keep velocity data in the logs. I generally do load development for group size, once I decide on the charge I want based on its ability to group then I'll shoot them over the chrono to get the velocity. I rarely care what the actual velocity is but I want to know it so I can calculate the trajectory. If you load ten rounds of each charge, at intervals of say 5%, and record every shot, calculate the averages, and plot them you may see a distinct curve. Or you may not depending on how good your data points are. If the loads are within a few fps of extreme spread I would think the data would be usable.

I did something similar many years back and posted it somewhere here.

I plotted the average speed (or perhaps it was just grains? ) and group size ... was interesting but I never bothered to do it again

[Oldbloke]

About 2 years ago I investigated this. I wanted to determine a powder weight for a mild load in my 30.06 using AR2208.
It was purely a desk top assessment based on manufactures printed date.

I found that it was more or less linear.
BUT,
This can change quickly as you approach max loads.
Or
With changes such as jamming the bullet into the lands.
Or
Different powder or bullet could also change it.


Jezzab,
Your just starting your journey. Can I suggest you initially focus on getting the basics right. Rather than look at the more technical side.

Edit: To clarify the loads I was looking at were well below recommended start loads.

[mchughcb]

The answer is they are not linear between min and Max and you can verify measuring the velocity versus grains. I just did this he other week and a log best fit will give a more accurate curve.

[Fester]

I would think there were too many variables to end up linear and it would change as you get near max loads.

I would stick with the basics and good case prep, stick to a std 20-30 thou jump as you don't want extra pressure spikes and stuff when pills are jammed.

I don't waste heaps of components and range time to get my loads anymore but still like to achieve a load that will be capable of a nice 1/2" group @100 or better.
They won't do it all day but nice to bring a hole-out 5-shot group or clover home from the sporter in any inherently accurate cal.

I now may start at say, halfway between min and max book load, could try a bit lower if suss.
Do a small sample of charges going up around .5 gr increments to around max or a tad over just to see if you find a nice node with group sizes
Can just do 3 shot groups if you shoot well and decide on group shapes to discount bad ones.
If I see where it is getting into a node, I then make some loads in smaller charge weight increments around that to fine tune at the next range day.

A common pattern I see with different cals is an accuracy node fairly low and the next is often around max or a bit over using ADI charts.
The higher charged loads do offer the benefits of flatter shooting at longer ranges if you see no pressure signs other than mild primer flattening.

Some loads I get with 1 test day and another to ensure it is repeated.
Other rifles have taken months with different powders to get a projy shooting well.
I just shoot through the chrono once at the end to be sure as I don't have a Garmin and we don't have a cheaper clone product as yet.

[mchughcb]

The most truthful statement I ever heard from a RO was the amount of people who burnt out varmint rifles thinking they could perform like a bench rest rifle.