Which data is more accurate

[gorillamotors]

I am trying to find load data for some 6ARC loads but not that much is out there so I am relying on Quickload, Gordons Reloading Tool, and Hodgdons website to make my decisions BUT.....

Hogdons website  shows 27.5-30.6 LVR  and for that load 2678-2957 ft/sec and 37800-51300 PSI pressure

QL use the same charge of 27.5-30.6 LVR and for that load 2555-2867 ft/sec and 34500-48400 PSI pressure

GRT use the same charge of 27.5-30.6 LVR and for that load 2759-3083 ft/sec and 39800-58400 PSI pressure

I am using the same information for all 3 loads: same bullet, same COAL, same trim length. Same everything.

The velocity is not that big of initially but the pressures are. Does Hodgdon do test firing for each load. I don't think so. What do you guys rely on to make your initial loads?

[grayfox]

I don't know for sure how much Hodgdon does as far as pressure testing, I've pretty much accepted that when they publish a pressure they did a test, at least the low and the high.
That being said, any ballistics program is only as good as its inputs and algorithms...
For QL and Grt it's known that they have some difficulty replicating performance of shorter, fatter cases like grendel and 6Arc... for either one you have to tweak things like actual case volume and sometimes other values.
So yeah, which one is accurate?
For Hodg I give them some benefit of doubt, bearing in mind that their results are also results from their gun...

Which load/bullet setup are you looking to start.

Most of the guys on here have trusted/used Hornady as being fairly accurate to start with, bearing in mind you might be using a non-hornady bullet.
For my new trials I try to get my start from Hornady data as much as I can do it.
Ex, for the 90 gr Sie Tgk I use a ladder from the Hornady 87 gr Vmax data. That sort of thing.

[gorillamotors]

I am using converted Lapua 6.5 Grendel brass, LVR or CFE223, 112 Barnes Match Burners. I too do ladder testing for my loads. I just loaded GRT the other day and was baffled about the various differences in the pressures. I have talked to Hodgdon and Alliant about 5-8 years ago and they both said that not all loads have been pressure tested. I thought that they might have pressure tested most all loads by now.

[r.tenorio671]

...due the possibility of "human input error", I take the QL & GRT data with a healthy grain of salt. If anyting I'll base my ladder tests on Hornady or Hodgdon data. I am confident both have done the appropriate pressure testing, especially since they put their data out in the public domain....there are legal ramifications involved there. I like that Hornady has data listed for gassers as having been tested in an AR format with an 18" barrel, it give a more "realistic" expectation.

....all of that being said, I still do my testing in my platform to determine what it tells me.

[grayfox]

One thing I do to tweak Grt is the sebert factor. Some reading I did said this factor is about how much powder goes down the pipe as it burns... or something like that. Anyway the Grt help screens said you might tweak this to get some smaller cases to be more accurately depicted. The base value is 0.5 IIRC, I bumped it down to 0.45 for grendel and 6 Arc, and it **seems** to have helped. I also, after I get some actual chrono data on my load combos, I usually adjust case "volume" (more on this in a minute) so that MV closely agrees to the real MV. Then I look at pressure to see where it lands.
On the "volume" another debate is ongoing on the smaller fatter cases, that perhaps the primer igniting bumps the bullet out before all powder ignites... meaning there is an effectively "more" volume that the powder sees as its "case volume". So in some sense case volume might not always be the volume inside the case (for these smaller fatter ammo's), if you know what Imean.
Now these things I do are not patented nor proven to be what you ought to do; they are just what I have tried to make Grt a bit more useful to me. Most times, after doing my tweaks and comparing/adjusting to real MV data, I think of the resulting model as good mostly for a 1-off adjustment, like swap out a bullet, or change barrel length, change powder up or down a bit, or maybe (Gasp!!!) swap the powder type and see I get... The farther "away" from the precise individual combo-model you go, the more suspect and room for error you're probably going. None of which, of course, is quantified. So. Be careful out there.

[StoneHendge]

To the extent that Hodgdon's isn't pressure testing every load, I'd be inclined to think that they have the most robust model.

[Lemonaid]

I think the Hornady data is better as it has both gas gun and bolt gun sections. GRT worked great for a load I checked using IMR 4895, but for Lever and CFE 223 it reports extreme danger for published Hornady loads. One smart GRT guy said the model works better for the stick powders for the 6 ARC.

[CZ527 Guy]

I am keenly listening. Can't help but think 30 years ago very few had access to equipment to accurately measure muzzle velocity. Suppose I am hoping to see greater access to verifiable pressure testing capabilities. How does an individual get started off in this line of work? Expect there are a few here myself included with the passion to move forward in this area of science.

As for the QL & GRT I expect a lot may be left to be desired in terms of accuracy. In the end actual testing is unbeatable. For some reason I was hoping for 6 ARC data from the likes of Nosler by now. suppose my expectations are a bit high. Hard to do much in the way of testing when nearly all components are in short supply.

[grayfox]

Getting "into the pressure business" will take some calibrated strain gages, and more stuff...
Could be $$$$.

LRRPF52 on 65Grendel forum, was involved along with some others in the early days of the grendel, doing and part of the pressure testing of grendel rounds/loads. Maybe if you're interested you might want to ask him for some info on all of it.

[GRH]

How does an individual get started off in this line of work? Expect there are a few here myself included with the passion to move forward in this area of science.

https://www.shootingsoftware.com/index.htm

[trianglevelvet]

GRT's model is a little off for 6arc.
Hornady's published loads all show way overpressure if you enter them into GRT.

Hornady, Hodgdon, and Lyman have 6arc published data.
Berger also published some data for 105's

Id trust tested published data over a simulation model.

It might be useful to adjust GRT to match the available published data. The Hodgdon and Lyman data sets have pressure listed.

[GRH]

GRT's model is a little off for 6arc.
Hornady's published loads all show way overpressure if you enter them into GRT.

Hornady, Hodgdon, and Lyman have 6arc published data.
Berger also published some data for 105's

Id trust tested published data over a simulation model.

It might be useful to adjust GRT to match the available published data. The Hodgdon and Lyman data sets have pressure listed.

I'm curious about that myself, I have A2520, Varget and TAC to try, all modeled with the same resulting over pressure warnings.

Everything is finally done and I'm planning on making some first loads today, so I'm looking forward to the results.

I'm going to start with 24.0-26.0 TAC in .5gr increments as it is more readily available to me, and see what the chrono has to say.

[Burt Gummer]

GRT's model is a little off for 6arc.
Hornady's published loads all show way overpressure if you enter them into GRT.

Hornady, Hodgdon, and Lyman have 6arc published data.
Berger also published some data for 105's

Id trust tested published data over a simulation model.

It might be useful to adjust GRT to match the available published data. The Hodgdon and Lyman data sets have pressure listed.

I'm curious about that myself, I have A2520, Varget and TAC to try, all modeled with the same resulting over pressure warnings.

Everything is finally done and I'm planning on making some first loads today, so I'm looking forward to the results.

I'm going to start with 24.0-26.0 TAC in .5gr increments as it is more readily available to me, and see what the chrono has to say.

Care to share the Lyman Load Data you have?

---

GRH

How does an individual get started off in this line of work? Expect there are a few here myself included with the passion to move forward in this area of science.

https://www.shootingsoftware.com/index.htm


Care to share the Lyman load data you found?

[GRH]

What I physically have loaded is based from published Hornady data for gas gun, and my 20", 1-7 barrel, and my particular chamber dimensions so it's nothing out of the ordinary.

as an experiment I input near low starting point of 25gr, all three appear very similar in case fill, velocity, pressure curve, peak pressure and even down low they all have over 85% burn and case fill.

It seems to follow the same loose trend as charges are increased, but with enough difference to make it worthwhile to find out which one would be best for a particular setup.

I don't think I made any referece to Lyman data, that was trianglevelvet.

If you are familiar with Discord, join the RLD Discord, 

https://discord.gg/reloading 

There are plenty of guys and gals who are happy share advice and load data in real time.