I've been using GRT for a while and a Patreon supporter, and forgive me if you already know...
Surprisingly many times barrel length is overlooked as the powder test barrels are usually 24" or so long and guys get all worked up about GRT being way off from their 16" Gov barrel.
Many of the supplied inputs are middle of the road averages or manufacturer supplied info. Things like real fired case volume, measured bullet jump, case length, measured dimensions of your bullets, and seating depth have a big impact.
Sebert factors have been updated and need to be input, selecting the correct IP for bullet type, OAL of actual reloaded ammo. Gas gun port loss can also be a small factor. Powder also has a fudge factor which is why you never (not supposed to) mix a partial can of a lot# with a different lot#.
All of which is essentially useless without actual chrono data. Just do your best to fill in everything you can as accurately as possible, and as always start low. Then you can measure fired case volume, input chrono results.
Then things can be adjusted to reflect what is going on in your rifle with the components you are using, after the model reflects chrono results, you can run OBT to find nodes.
I'll suggest reading the manual supplied in GRT program as it covers about everything, and there are YT videos also. There is Patreon that is very helpful and you get to talk to smart users from around the world.
I don't know if there are less users in the states or if they(we) are just lazy, but it appears most of the user input seems to come from Europe.
GRT is entirely dependent on user input from real world results, so I do my best to always upload any data I get because it makes the powder database that much more reliable.
Surprisingly many times barrel length is overlooked as the powder test barrels are usually 24" or so long and guys get all worked up about GRT being way off from their 16" Gov barrel.
Many of the supplied inputs are middle of the road averages or manufacturer supplied info. Things like real fired case volume, measured bullet jump, case length, measured dimensions of your bullets, and seating depth have a big impact.
Sebert factors have been updated and need to be input, selecting the correct IP for bullet type, OAL of actual reloaded ammo. Gas gun port loss can also be a small factor. Powder also has a fudge factor which is why you never (not supposed to) mix a partial can of a lot# with a different lot#.
All of which is essentially useless without actual chrono data. Just do your best to fill in everything you can as accurately as possible, and as always start low. Then you can measure fired case volume, input chrono results.
Then things can be adjusted to reflect what is going on in your rifle with the components you are using, after the model reflects chrono results, you can run OBT to find nodes.
I'll suggest reading the manual supplied in GRT program as it covers about everything, and there are YT videos also. There is Patreon that is very helpful and you get to talk to smart users from around the world.
I don't know if there are less users in the states or if they(we) are just lazy, but it appears most of the user input seems to come from Europe.
GRT is entirely dependent on user input from real world results, so I do my best to always upload any data I get because it makes the powder database that much more reliable.
SI VIS PACEM, PARA BELLUM