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Hi all
I have just started to play with GRT and was wondering if there is any comment on the accuracy of the predictions? Seems like a very good guide with almost every possible powder and projectile in the database.
Thanks for your comments in advance.
Ruger7mm
It is an excellent tool, but like all tools responds best with good inputs, if you take the trouble to accurately measure case capacity and the other usual measurements, then chronograph a first few test rounds, it will be close. If you then use the OBT tool and calibrate actual velocity to predicted it becomes very accurate indeed. I was just using it tonight, went to the range this arvo and the second string of a load started showing pressure signs, then popped a primer. Back home, calibrated GRT and sure enough 68,000 psi - way too much and due to seating depth.
As above, really usefull especially when you recalibrate a burn rate or estimated V with validated speeds. Been using it for maybe 4 yrs.
Usually within 20 fps often much closer.
Thanks for the replies, it looks very detailed so will do some case volume measuring for the cases of the different calibres I am loading for, and get to more fun at the range. Thanks again.
Ruger7mm
@Ruger7mm havent read this post myself but it may hold some good info on using GRT
https://forum.accurateshooter.com/th...#post-38835206
Thanks John
Looks very helpful and informative. Will have a play tonight. I have done the water volume, projectile length, and other parameters that I can measure to help with load development and for GRT to estimate the pressure and velocity. I have loaded some combinations up for the 284 and will test at the range next week to see how they compare.
Cheers Ruger7mm
One thing to be aware of with GRT is "jamb" . I'm using it on some 223 loads I'm playing with just now, and with load with "a" it was within 15 fps of prediction, but I had some unexpected pressure signs on the load with projectile "b" as I hadn't taken into account that the different profile of the projectile was taking it up to the lands even though both loads were the same COL.
Last I heard a team was building a new version. Has anyone heard when it will be ready?
amazing tool. Was within 10 fps for the loads that I actually shot.
But if course depending on circumstances it might be further off.
its free and in my opinion a lot better interface than quickload.
https://grtools.de/doku.php
One method I use (wrong or right I don't know).
If the measured velocity (true velocity from chronograph) is off from the estimated velocity, play with the Ba figure (brisance) in the powder section. Until you get readings that match or are close to the truth.
Some of the powder profiles/ models are 5 or 6 yrs old and may not be accurate for current burn rates
I found this. So sounds like abt april-may.
Dated 14/12/24
We have a fully functional GRT (called GRT NextGen) implemented in Node.js on top of Electron which looks and works identical to GRT classic, but without all the wizzards and andvanced reporting, OBT, tables and the like. While everybody was enjoying more or less a break in 2024, there are still options to add some of the missing functionality in the upcoming Months and Years. I know <@1023223992808648734> and <@564163449710575657> had ideas for a better (Improved GRT) numeric core following a fully isotropic approach and I believe this could possibly implemented in the foreseeable future. It might be an experiment though, as there where concerns on wether our current powder model would be usable. Long story short: there is some thinking behind the scenes going on, not much has materialized in 2024, but there is still work to be done.
Reply same day:
Not to throw in a monkey wrench, but what is sorely needed is a mathematician(s) that can reverse the algorithm so that with an input of several load ladders from several weapons, the output would be a list of propellant model parameters. This sounds simple if we look at simple algorithms like A x B = C, the solution is C / A = B, or C / B = A. If we do not know either A or B, knowing C is not very useful. However, with the current internal ballistics algorithm there are 7 parameters, all of which are unknown unless the manufacturer is willing to provide several parameters (i.e. Qex and Pc). There would be 5 parameters remaining to be synthesized. That is a daunting task. Some of the parameters can be guessed at based on particle shapes (Pc), but this is haphazard to say the least. So if anyone knows of a mathematical genius that would volunteer, let us know.
If you happen to use the discord app, join the GRT discord group. It is a wealth of information and probably the best group out there for reloading related information and conversation.
Also different batches may be slightly different, I've noted one from ADI which was about 40fps slower just changing bottles. No real effect in anything major for what was effectively a bush load.Quote:
Originally Posted by johnd
I am not able to change the units from mps to fps etc.
I would appreciate any help. Thanks
In compact mode:Quote:
Originally Posted by Nakihunter
On the results page. Just above the graphs where all the data is:
Move mouse over the muzzle velocity, e.g. 2700ms
L mouse button, click on the velocity e.g. 2700
It will change to fps
On the other thread:Quote:
Originally Posted by Nakihunter
"Under the view tab, select change all units to fps"
Doesn’t work for me. Only options I have is default, metric or imperial. None of those give fps. I just have a conversion sitting open in another tab.Quote:
Originally Posted by Oldbloke
Imperial should give you feet per second, metric would be meters per second
Each input or output has option for imperial or metric. Hover the mouse over the right hand edge of the field you want to change and a wee symbol of a ruler comes up. Click on it and it converts to other units. This applies only to the individual field you’re interested in
@NakihunterQuote:
Originally Posted by Oldbloke
Did you try the above?
Thanks guys. I'll check this long weekend. Cheers.
Rookie mistake, I was looking at projectile speed on the right not MV on the left… so yep works as it should…