Do we trust Gordon's Reloading Tool?

[Desperatezulu]

I'm loading Somchem S365 (local) 35 gr charge weight with a 100g Hornady Interlock.

I plotted some lines on a graph based on charge weight vs f/ps to get a general idea of the speed I'd get with my powder selection. I expected I could get a good feel about what speeds to expect when pushing to the max figure. Now I trust this output for other reasons and perhaps I'm out by 40 f/ps either way because the powder manufacturer tests on a 24" barrel, but if was serious about the accuracy of the graph I would crono this load to compare. Gordon's tells me I'm at 2400 f/ps with my load where I think I'm around 2700 f/ps, assuming the relationship between speed and powder is linear. It might not be but only by a small amount imo.

I've highlighted some of my preferred loads by adding either the speed I want or the load I want.

243, Hornady 100g SP, Somchem S365

www.desmos.com

It sounds like you have not chrono'd your loads?
If not, none of your conclusions are vaguely valid - just speculation. Questioning the veracity of GRT (or any other internal ballistics software) without following any basic load development and testing procedures is focusing on the wrong place. What is your case capacity (gr H2O?) - after muzzle velocity, this is the next biggest variable.

Regarding the simulation that GRT does on different powder types - they use empirical data fed back by users to test and refine the powder burn rate simulation. So it is not just theoretical. My experience with it has been that it is very powerful and accurate if good data is inputted.

Secondly the relationship between powder charge and velocity is not linear. This may be an ok assumption for small increments but it is not appropriate for a big range such as the difference between min and max.
To compound the risk factor, Somchem S365 is notorious for its unpredictable (read NON-linear) behaviour - certain lots were recalled and are recommended to avoid. It is not a powder to be exploring the limits of with casual reloading/load development practices.
More than a few 243s went kaboom with one of the hot lots (I think Lot 71?)

Do I take the risk and load over the manufacturer max value?

Unless you follow proper load development practices, whatever reloading you do is going to be risky. WIthout measuring, you just don't have any idea how close you are to disaster.

 

[Creigh]

It sounds like you have not chrono'd your loads?
If not, none of your conclusions are vaguely valid - just speculation. Questioning the veracity of GRT (or any other internal ballistics software) without following any basic load development and testing procedures is focusing on the wrong place. What is your case capacity (gr H2O?) - after muzzle velocity, this is the next biggest variable.

Regarding the simulation that GRT does on different powder types - they use empirical data fed back by users to test and refine the powder burn rate simulation. So it is not just theoretical. My experience with it has been that it is very powerful and accurate if good data is inputted.

Secondly the relationship between powder charge and velocity is not linear. This may be an ok assumption for small increments but it is not appropriate for a big range such as the difference between min and max.
To compound the risk factor, Somchem S365 is notorious for its unpredictable (read NON-linear) behaviour - certain lots were recalled and are recommended to avoid. It is not a powder to be exploring the limits of with casual reloading/load development practices.
More than a few 243s went kaboom with one of the hot lots (I think Lot 71?)


Unless you follow proper load development practices, whatever reloading you do is going to be risky. WIthout measuring, you just don't have any idea how close you are to disaster.

I could buy a chronograph or I could buy ammo. That's just how it wen't. But you're not wrong about that being the next step.

 

[HWL]

Can't get in South Africa.

View attachment 644274

Shipping stuff to South Africa is horrible. More is stolen than arrives.

HWL

 

[sgt_zim]

I could buy a chronograph or I could buy ammo. That's just how it wen't. But you're not wrong about that being the next step.

A chrono will end up being less expensive over the long run than the ammo will be.

Say you zero your 243 at 100M. Since you don't know the velocity, you're going to need to put several rounds in a target at 200M, and at 300, and maybe at 400 and 500 to figure what the ballistic arc actually looks like. That's a lot of time, bullets, powder, and primers wasted just to figure out your ballistics.

 

[Creigh]

A chrono will end up being less expensive over the long run than the ammo will be.

Say you zero your 243 at 100M. Since you don't know the velocity, you're going to need to put several rounds in a target at 200M, and at 300, and maybe at 400 and 500 to figure what the ballistic arc actually looks like. That's a lot of time, bullets, powder, and primers wasted just to figure out your ballistics.

Seriously, I don't disagree, but it's a new rifle and I've only put in 20 rounds through it. It's a tough ask to buy a new rifle and just let it stand there while I wait for a chrono.
That's why most of my work is theoretical, but Gordon's looked promising and I needed to know what most people's experience was.
And correct me if I'm wrong, but feet per second isn't something that I add to a Gordon's query.

 

[sgt_zim]

Seriously, I don't disagree, but it's a new rifle and I've only put in 20 rounds through it. It's a tough ask to buy a new rifle and just let it stand there while I wait for a chrono.
That's why most of my work is theoretical, but Gordon's looked promising and I needed to know what most people's experience was.
And correct me if I'm wrong, but feet per second isn't something that I add to a Gordon's query.

You can add them after the fact. If measured MV is fairly off from what GRT predicts, Charlie can help figure out what's wrong with a given config. One thing GRT doesn't do is account for jump, located at the very bottom left of cartridge input. If you actually know your jump, put it in, but the base calculation on pressure/MV with 0 jump is always higher/faster than actual

 

[analog_peninsula]

When I get a new rifle, I always fire a nominal load of modest pressure to get some kind of pressure/velocity baseline. A couple of reference loads is even better. In the past, I’ve tested loads of identical book velocity and had actual velocity readings as much as 175 fps+ apart. I no longer view published data as anything more than a general guideline. The one caveat is that I view velocity as an accurate indicator of chamber pressure, and don’t expect any free lunches. I know some of the modern powders are minor exceptions to this rule, but even there, I try to exercise good judgement.

 

[Creigh]

When I get a new rifle, I always fire a nominal load of modest pressure to get some kind of pressure/velocity baseline. A couple of reference loads is even better. In the past, I’ve tested loads of identical book velocity and had actual velocity readings as much as 175 fps+ apart. I no longer view published data as anything more than a general guideline. The one caveat is that I view velocity as an accurate indicator of chamber pressure, and don’t expect any free lunches. I know some of the modern powders are minor exceptions to this rule, but even there, I try to exercise good judgement.

This is my approach so far. I care about not going over max but not losing out on some of the potential energy that might still be available to me.

 

[Creigh]

You can add them after the fact. If measured MV is fairly off from what GRT predicts, Charlie can help figure out what's wrong with a given config. One thing GRT doesn't do is account for jump, located at the very bottom left of cartridge input. If you actually know your jump, put it in, but the base calculation on pressure/MV with 0 jump is always higher/faster than actual

How do you explain the big differences to the calculation with regard to jump when Gordon's seems to know the COAL for that particular bullet in that chamber? Is "Every rifle is different" simply because of the age of the barrel or is it that some manufacturers have strayed from specification?

Appreciate everyone's input.

Edit: I guess what I'm asking is why is there such a big difference in jump between different rifles. I would have thought there would be zero outliers for jump.

 

[sgt_zim]

How do you explain the big differences to the calculation with regard to jump when Gordon's seems to know the COAL for that particular bullet in that chamber? Is "Every rifle is different" simply because of the age of the barrel or is it that some manufacturers have strayed from specification?

Appreciate everyone's input.

Edit: I guess what I'm asking is why is there such a big difference in jump between different rifles. I would have thought there would be zero outliers for jump.

Because for reloaders, it's assumed that we're going to be playing around with the COAL for the most accurate load. So GRT just leaves it at a default of 0.