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Maybe I'm late to the party, but been reloading now a couple of decades. Interested to hear users experiences with GRT as an aid in load development--good, bad, accurate, etc.? There are so many holes in manufacturers data with respect to new propellants/powders and new projectiles, complicated by the lack of availability of all of the above that I find I need to create loads out of whole cloth, and I'd like to have a baseline in facts or at least a SWAG. Already installed GRT and playing with it.

I've just started playing with this as well. Still learning how to use it.

I've used GRT a little and found that it yields results very similar to QUICKLOAD results. I know that for some cartridges QL gives erroneous solutions, but I don't load any of those myself. I think GRT takes user reports to fine tune their algorithms and that may set it apart from QuickLOAD for those cartridges, but I'd not assume that.

GRT is dependent on users submitting accurate data. Popular cartridges with lots of data submissions like the 6.5 CM for example, have been spot-on running what-ifs for me.

However, not-so-popular cartridges such as the 9.3x62mm? The predictions are not even close.

This doesn't lend much encouragement . . . .
Quote from GRT site

"Important announcement

I just wanted to reach out and let you know that my husband Gordon passed away on January 19th 2022.

Until further notice, this site stays online. Please note that Patreon contributions have been paused.

Initially, no additional submissions should be made to the GRTLab, or Translations, as no one has access to service the data.
Therefore, it will be impossible to update Powder Models, Calibers, and Bullet to the GRT database as an official release until the possibilities of continuing Gordon's fine work are explored.


Take care!
Chrissi "

Oh boy...

I'm a first time user. I've started with inputting the specs for a 357 herrett since it wasn't in the database. I've not compared results to my barrel, only to the reloading manuals. Results have been within 10%, often closer. I've got some fine tuning to do as several case and chamber dimension inputs were swags or incomplete cartridge diagrams when available. I can't make the bore cross section error message go away. It says input is physically impossible. Not sure what i'm doing wrong here.

A screenshot of what you're seeing might be helpful.

This is the message i get

Is Gordon's a free site or a program you purchase?
Soup

it's free. just download it and run.

I think the value entered in that field is miscalculated. I am not familiar with the .357 Herrett so I'm not sure whether it's a .357 or a .358, but if you pull up other cartridges in the database you can see what the value should be. For .35 Whelen (.358") it is 63.780 mm sq, and for .357 Magnum it's 62.570 mm sq in the GRT database. Try one or the other and see if that issue goes away. If it was me, and I wasn't sure, I'd stick with the .357 Mag dimension just for the sake of safety.

Personally I would go to View/Change all units/imperial. Sometimes computer programs get confused when some of the settings are metric but others imperial which is the situation you have.

I've tried several different entries from 63 to 65 and the error message remains. Changed all variables to metric, then imperial and still it remains. I did finally get to fire the gun for the first time over my chronograph and compare numbers with GRT.
GRT predicted 1790 fps and 3600 psi
Measured actual velocity was 1,500 fps and pressure too low to fireform to a sharp shoulder.

Changing effective barrel cross section between anything reasonable could not bring the numbers to agree. I'm working on every variable to make sure the parameters are accurate.

GRT has been spot on for me with powders that have a high calibration...except for Vihtavuori N105 and 300 blackout subsonic loads. GRT overestimated velocity by > 200 fps.

it's quite useful but it's not gospel. one thing I found that I know isn't right. is a 45.5 grain load of varget in a 308 with a 168 Barnes my gun yields 2740 with that load and it is a published load. but GRT says it's over 80,000 PSI.. which I'm pretty sure is not right even if you loaded it up in mil-spec brass I don't think you would get that high a PSI. but I haven't went through and done though water grain entry and all that for specific brass

Nosler says 46 C with standard cup and core.

Hodgdons says 45.0 C

Barnes says you are 1 grain over max.

I think I just typed the number wrong on here it is 44.5 I will confirm that when I get home and re-enter it and see if I typed it wrong there also.. 99% sure I am not a grain over I am at bookmarks I will look at this tomorrow when I get back..

The 44.5 with Barnes seating depth works. GRT defaults to 56.8 grains water CC, go up to 58 grains CC it works better. Take it down to 54 CC and it doesn’t even work at 44.5. 45.5 never works.

what books that out of ?
mine's the Barn's number four