And Hornady does that too.
GRT numbers
- Thread starter marchx
- Start date
jxb
Gold $$ Contributor
VV wouldn't be the first manual to have bad numbers in it and this is why I generally consult at least two sources of load data before I start then set max to the lower max of the two, then start well below that max.
Worse case doing that is I start too low and never find pressure or expected velocities during that testing session. I'll take having to do another session every time over possibly starting testing above max pressure.
When I ran the GRT numbers for this above, if I was using the VV numbers and started mid range I'd be at GRT max. If GRT was correct it might be a bad day...
Worse case doing that is I start too low and never find pressure or expected velocities during that testing session. I'll take having to do another session every time over possibly starting testing above max pressure.
When I ran the GRT numbers for this above, if I was using the VV numbers and started mid range I'd be at GRT max. If GRT was correct it might be a bad day...
Fast14riot
Gold $$ Contributor
Only times I ran into way off numbers in GRT was with a powder not listed and I did a ton of research to figure out the closest model. I was trying to figure out XMR4350 in a 6x250 with 106eps bullets. I even modeled the case, chamber and bullet in the cartridge designer, and even then my starting loads were at max pressure on 105° day. Flattened primers, blanked one or two. From there I just dropped my charge appropriately.
Printed manuals can be way off, too. I found that Hodgdon data for 30-06 with 175smk is very hot. They list starting loads higher than Sierra max loads and a couple other manuals slightly overlapped with max loads at Hodgdon starting loads, even for the same brand case.
Printed manuals can be way off, too. I found that Hodgdon data for 30-06 with 175smk is very hot. They list starting loads higher than Sierra max loads and a couple other manuals slightly overlapped with max loads at Hodgdon starting loads, even for the same brand case.
How Do “They” Develop Load Data?
This is something I’ve often wondered.
I see some powder supplier’s data, let’s use Hodgdon as an example, includes pressure for min and max loads along with velocities. I assume these data are developed with test barrels and pressure measuring equipment which I also assume conforms to SAAMI specs.
I see bullet makers, use Sierra and Hornady as examples, do not include pressure data, lump numerous bullets together and only specify velocity in round numbers such as 2600, 2700, 2800 fps. They will even specify which firearm was used in development, so not a SAAMI test barrel.
So I wonder, especially when it comes to the bullet makers but also the powder suppliers, has someone actually assembled, fired, and tested all of these bullet and powder combos we see in all of this published data, or is some of it estimated, maybe using software and accurate modeling?
This is something I’ve often wondered.
I see some powder supplier’s data, let’s use Hodgdon as an example, includes pressure for min and max loads along with velocities. I assume these data are developed with test barrels and pressure measuring equipment which I also assume conforms to SAAMI specs.
I see bullet makers, use Sierra and Hornady as examples, do not include pressure data, lump numerous bullets together and only specify velocity in round numbers such as 2600, 2700, 2800 fps. They will even specify which firearm was used in development, so not a SAAMI test barrel.
So I wonder, especially when it comes to the bullet makers but also the powder suppliers, has someone actually assembled, fired, and tested all of these bullet and powder combos we see in all of this published data, or is some of it estimated, maybe using software and accurate modeling?
Many of the load manuals do list their method. Hornady in particular Uses SAAMI methods for pressure but then shoot the bullets in real rifles (mostly) to determine velocity. Sierra in Edition V used actual rifles. Sierra redid most of the data using SAAMI for Edition VI. Don't know if they used real pressure measurements or typical pressure signs. I received load data from Berger that said it was from Quickload. Hodgdon lists actual pressure (either CUP or PSI) so it appears they do SAAMI type testing. Lyman list pressures and in many cases list firearm as Universal Receiver so it is likely they used SAAMI test barrels and methods. Vihtavouri probably uses CIP methods. It is important to also understand that a loading manual maximum load may not be at maximum pressure. In the Hornady case they shoot the maximum test safe pressure in a real rifle, obtain the maximum velocity and then appear to report the data rounded down in 50 to 100 ft increments.
All the manufacturers list their maximum load as safe and nothing more.
I recently had an interesting case with VV in that they listed maximum load in the 2020- 2023 Manuals in 308 with 168 SMK and N135 as 42.1gn/2697 fps. The 2024 Manual lists 40.1gn/2569. Capstone response was use the lower data for safety! Powder change? CIP pressure change? Who knows?
dstoenner
Silver $$ Contributor
Sorry I am getting into this thread late. GRT can treat your rifle/barrel/cartridge as a system and curve fit the powder to match. I wrote up a method of getting a load in 50 shoots. Here is the thread on here:
Hope that clears up somethings. And yes you have to have all of the mechanical values correct or as one person said, Garbage In = Garbage Out
David
How to get a load in 50 bullets with Gordon's Reloading Tool (GRT)
There have been a few threads on here about GRT. I have been using it for over 2 years now. As an electrical engineer, I am used to simulating systems to see the response. GRT is just exactly that but the "trick" is how to coax it into giving you a good answer. That took me some time to...
forum.accurateshooter.com
Hope that clears up somethings. And yes you have to have all of the mechanical values correct or as one person said, Garbage In = Garbage Out
David
Never liked computer guestimates. I go by real results published in reloading manuals as a guide. I'm a varmint hunter. I look in the manuals for my bullet wt. I find the powders that give the highest FPS. Then see if any of them are usually available. I quickley find a couple of powders that work.
Many of the load manuals do list their method. Hornady in particular Uses SAAMI methods for pressure but then shoot the bullets in real rifles (mostly) to determine velocity. Sierra in Edition V used actual rifles. Sierra redid most of the data using SAAMI for Edition VI. Don't know if they used real pressure measurements or typical pressure signs. I received load data from Berger that said it was from Quickload. Hodgdon lists actual pressure (either CUP or PSI) so it appears they do SAAMI type testing. Lyman list pressures and in many cases list firearm as Universal Receiver so it is likely they used SAAMI test barrels and methods. Vihtavouri probably uses CIP methods. It is important to also understand that a loading manual maximum load may not be at maximum pressure. In the Hornady case they shoot the maximum test safe pressure in a real rifle, obtain the maximum velocity and then appear to report the data rounded down in 50 to 100 ft increments.
All the manufacturers list their maximum load as safe and nothing more.
I recently has an interesting case with VV in that they listed maximum load in the 2023 Manual in 308 with 168 SMK and N135 as 42.1gn/2697 fps. The 2024 Manual lists 40.1gn/2569.
Shoot your starting charge (55 gr) and then calibrate GRT to predict where you’re going to hit pressure. I just did the same with a new barrel, VV 165 and 180 hybrids. 57 grains put me about 2870 in a 32” barrel and that was a little higher than the GRT estimate.
dellet
Gold $$ Contributor
Not sure about Gordon’s, but with quickload it generates a mean/average data set. Then also generates predicted lot to lot variations. That’s the first place I look when an anomaly like this happens. I have found more than one instance where initial predictions were off 5-10% on pressures. But within the high load window of quickload.
RegionRat
Gold $$ Contributor
As someone who worked in this field for a lifetime, I will only add that if I could change something about GRT or QL, it would be to require a training session before hand.
I know that sounds harsh, but then again I don't like leaving things like software tools that are easy to misunderstand up to luck with the users.
GRT and QL just don't come with enough background to start from zero and get an 95% user-success rate.
The varied backgrounds of folks who take these software packages and don't understand the pitfalls almost guarantees trouble, just like the kind in this thread.
I only hope the OP will take a pause and keep the faith. Be patient and give yourself time to learn the issues and effects of each user input and also the ones supplied by the software tools.
Two things will happen. One... The inputs will improve and the program prediction estimates will land closer to the actuals. And the two.... is the education in understanding that these are simplified models and cannot be expected to account for all the tolerances in barrels, actions, bullets, powders, primers, brass, etc., but they come "close enough" in the right hands to be useful.
It is that understanding of each parameter and how sensitive the pressure can be that is a longer lesson. That takes multiple outings with multiple guns/recipes and component lots to learn. Be patient but know that complicated physics models are full of this sort of problem such that if you don't have the stomach for this, best to leave it alone. I hope the OP toughs it out.
I know that sounds harsh, but then again I don't like leaving things like software tools that are easy to misunderstand up to luck with the users.
GRT and QL just don't come with enough background to start from zero and get an 95% user-success rate.
The varied backgrounds of folks who take these software packages and don't understand the pitfalls almost guarantees trouble, just like the kind in this thread.
I only hope the OP will take a pause and keep the faith. Be patient and give yourself time to learn the issues and effects of each user input and also the ones supplied by the software tools.
Two things will happen. One... The inputs will improve and the program prediction estimates will land closer to the actuals. And the two.... is the education in understanding that these are simplified models and cannot be expected to account for all the tolerances in barrels, actions, bullets, powders, primers, brass, etc., but they come "close enough" in the right hands to be useful.
It is that understanding of each parameter and how sensitive the pressure can be that is a longer lesson. That takes multiple outings with multiple guns/recipes and component lots to learn. Be patient but know that complicated physics models are full of this sort of problem such that if you don't have the stomach for this, best to leave it alone. I hope the OP toughs it out.
Dimner
I do believe in Captain Crunch.
In the 3006 and 7x57 mauser with n140/150/160 I have found VVs numbers to be waaay off.
But then again in my experience GRT has been nearly right on or sometimes comically underestimated real world velocity and thus pressure. Back when I used quickload exclusively, I could depend on every powder and cartridge combination to be overestimated velocity wise until I put in real world velocity results and changed the Ba value. And I liked how it over estimated velocity, it acted as a safe guard to work up my loads.
When I first started using GRT I found it was much more hit or miss. Then I started working with VV powders and things were never matching in their manual and GRT. Never could accurately estimate velocity or pressure using GRT and or the VV manual. It's a total crap shoot
So my new practice is to just use a middle of the road VV manual load, make up 3 rounds, subtract a grain, make up 3 more rounds and then go collect actual velocity data. Then using this data to modify the Ba in GRT it all comes together for all future testing with the powder/cartridge combo
Edit to add, I'm always using actuals for h20, trim, coal, bullet etc.
SteveOak
Gold $$ Contributor
It is more likely you missed a setting or input than it is GRT being off by anything like that much.
Dimner
I do believe in Captain Crunch.
It's perfectly usable and spot on when you change the burn rate after one session of actual velocity results. After the user does that... I find it's plus minus 10fps predictable.
How likely it is based on the grt screenshot I posted?
jelenko
Gold $$ Contributor
Just to confirm. I got the same results in GRT.
I used the data stored in GRT for the chamber and bullet; added the COAL, the powder and charge amount from VV's website and got the same results as marchx.
I have no experience with the 284 win, but either GRT's calculations are incorrect or VV's numbers are incorrect.
jelenko
Gold $$ Contributor
Good point. It would be interesting to calibrate GRT with a mid range load.
Monte F
Silver $$ Contributor
GRT predicted velocity for 308 win. with exact measurements for the bullet and OAL where within 5 FPS of the actual from the Garmin. This is using Varget not VV. I will have to load some VV150 and check the numbers, but so far the numbers have been very close. As far as the numbers from VV, I find them very conservative for what is used in reality in F-TR. I always start on the low side to be safe and not ruin new brass (stretched primer pockets on the first firing).
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