LRRPF52 Wrote:We have so much industry pillar (AA, Hodgdons, Hornady, Nosler, Sierra, Western, Vihtavuori) pressure-tested data and have had most of it for so long, that I dont know why anyone would still use inaccurate predictive models.
The first three statements of my OP
SCJim Wrote:A few months back I bought 1000 Lapua 120 gn Scenars specifically for my 6.5 Grendel but never got around to it until a few days ago. Looking through my powder locker I noticed I had several pounds of Leverevolution powder so I decided that would be the powder I would start with. Official sources for 6.5 grendel load data for both the powder and the bullet is scarce as hen's teeth so I had to use internet postings, Quickload, and Gordons Reloading Tool. I personally prefer GRT over Quickload so I decided to use it for the development,but that is purely a personal preference. Bearing that in mind, here is some legalese
CAUTION: The following post includes load data generated by calculation in Gordon Reloading Tool (GRT) software is based on particular powder lots, the assumption the primer is as mild as possible, and assumptions about component, chamber and gun geometry that may not correspond well to what you have. Such data should be approached by working up from published starting loads. USE THIS DATA AT YOUR OWN RISK. Neither the writer, nor GRT's author assumes any liability for any damage or injury resulting from use of this information or information derived from it.
One of the first steps in using any ballistic software is putting all the parameters from your rifle into it. Barrel length, twist, gas port size and location etc come into the equation and can affect the outcome. GRT seems to be on the conservative side but do use common sense and caution and check for overpressure signs at every turn.
I find GRT's output to be reasonably close and a bit on the conservative side on all the predictions IF I take the time to adjust all the variables to my rifles configuration and shooting conditions. Of course if you just use the programs standard data values it will be garbage in/garbage out. I own relatively new versions of Sierra, Hornady, Nosler, and Berger load manuals and have all the powder manufacturers load data sites book marked. Data for Lapua bullets is rare as hens teeth in every cartridge. I still find GRT to be extremely useful and even use it to fine tune load data which I found in the books and on the sites.
While it is not perfect I have yet to find any factory load data that accurately represents and rifle I own so published load data never accurately predicts the velocities either. Most published data will use a 24 inch test barrel for bolt guns. Not a single one of my bolts rifle have a 24 inch barrel. Most are 26 - 30 inches with my bench rifles being on the shorter side. Rarely do the powder manufactures have data for the bullet I am using and the bullet makers may or may not have data for the powder I am using. When developing a load I never rely just on a single source, even when I can find data using the same bullet and powder and I always start at the lowest charge and work my way up shooting over a chronograph while inspecting every piece of brass fired. Closest I ever came to having a issue was using Hodgdon data for the 260 Remington with H4350 and 142 SMK's. I fired exactly 2 rounds before packing up and heading home and double checking everything. Turned out the Hodgdon starting load for the 260 was 2 full grains higher than the maximum load for the 6.5 Creedmoor. The Remington case volume is only a couple of tenths more than the CM. Since that incident when loading for the 260 I always check the data for the CM to make sure they are at least close and other than that one incident they always are.
Just out of curiosity can you name a published source that uses a Lapua 120 gn Scenar, Hodgdon Leverevolution powder, 20 barreled inch Grendel gas gun being shot in 85 - 90 F temps ? No ? How about data for a 30 Grendel with 115 gn bullets and N120? Crickets on that one too? Well that is why I use GRT. While not 100% accurate GRT gives me a good starting point that while may be a tad on the conservative side is a lot better than just pulling a starting point out of thin air.