I have downloaded Gordons Reloading Tool and have been working on getting it down. Lots of data points to enter. I did a web search on calculating for semi auto and cannot find the function to enter gas port length to work on semi auto (AR). As far as critical data points, I have measured true case capacity in grains of water and have entered OAL and jump to lands. Lastly, when taking calculated vs actual velocities what function is used for truing actual velocity? thanks
Gordons reloading tool, what data points are important and how do you enter the gas port length for calculating semi auto?
- Thread starter Markbsae
- Start date
I can't answer the first question. But, I'm happy to share my personal experiences with grt. I've been using it for about 3 years now fairly regularly and have been very happy with it. I've found that proper case capacity is definitely a must if you want accurate information. I would say the more PROPER data that you can input the better it works. If you're reloading for a few of your personal rifles and ammunition profiles take the time to put in as much of the information as you can. On the left side of the screen where you input rifle data make sure your barrel length and twist rate are as close to correct as possible, which will help in your optimum barrel time calculations. Also in that section the proper case length, overall case length, and case capacity are important to ensure proper load ratios when it calculates pressures and burn rates. Once you save these they are very easy to come back to.
In the bullet section make sure that the bullet dimensions that are in the database are actually correct. I've found on a handful of occasions they tend not to match up and need some adjustments. Sometimes I will just add those dimensions from scratch. With most berger bullets for example you can find all of the published bullet parameters right on bergers website. Also in that section you can click on the star closer to the bottom of the section to put the proper type of primer in. I've found this does make an important difference in the simulated calculations.
The powder section can be tricky. While most of the powders seem to be pretty close, I've found that sometimes the numbers for bulk density and energy (j/g I think?) can be off... The rub here is that Ive found it very difficult to find the proper numbers to compare for any powder manufacturers other than vhitavouri. I have found vhitavouri's numbers published on their site and changed them in grt which has proven to be incorrect on grt previously. Making me wonder how accurate the other powders are in their database.
When it comes to trying your velocity to calculate barrel time. You do need a chronograph measurement for a specific powder charge that you loaded up. So as an example: if you have your specific gun and bullet and powder input into the software and you loaded up say 45 grains of varget in x-load... It will give you the estimated velocity in the top big box on the right. Now if you click on the obt button the very first screen will open up and it will use its calculated fps. So say the calculation is 2835 with that load, but you're seeing 2855 on your chronograph, then you can adjust it right there to allow it to help you calculate a more proper obt charge. I've also found that sometimes that suggested obt charge weight can still use a little tweaking. So if you put that suggested charge weight on your main screen, you can go up to the big box on the right, and the last two numbers in the left column of that box will be your "optimum" time and "actual" time (if I'm saying this correctly) this can still be fine tuned until those numbers are as close as possible. (I usually do this by adding or subtracting a tenth of a grain of charge weight at a time in the powder section). While paying close attention to the load capacity and safe working pressure.
A lot of times when I'm developing something new I'll find that some of the powders recommended in the charge weight recommended, aren't giving 100 percent or close to 100 percent powder burns. So I will have a tendency to play with different powders until I find a combination that gives me a good case fill (this is where your case dimensions and volumes are important) and a proper powder burn. I personally like to see as close to 100 percent burnt powder as possible. Keep in mind sometimes you can also adjust your seating depth to help massage these numbers. Without diving too deep in this post, I suspect that this is helping finetune your powder charge test and seating depth test simultaneously.
I've gone as far as putting all my chronograph numbers in a long with chamber pressure measurements (I have a pressure trace system that I use) and you can get very accurate refined load information. So I guess the long and short of it is put in as much proper information in as you can and you will receive more realistic data. Garbage in garbage out... There is a lot more in this software. I've added full wildcat cartridge and chamber dimensions but that's a whole other rabbit hole.
Hope this helps
In the bullet section make sure that the bullet dimensions that are in the database are actually correct. I've found on a handful of occasions they tend not to match up and need some adjustments. Sometimes I will just add those dimensions from scratch. With most berger bullets for example you can find all of the published bullet parameters right on bergers website. Also in that section you can click on the star closer to the bottom of the section to put the proper type of primer in. I've found this does make an important difference in the simulated calculations.
The powder section can be tricky. While most of the powders seem to be pretty close, I've found that sometimes the numbers for bulk density and energy (j/g I think?) can be off... The rub here is that Ive found it very difficult to find the proper numbers to compare for any powder manufacturers other than vhitavouri. I have found vhitavouri's numbers published on their site and changed them in grt which has proven to be incorrect on grt previously. Making me wonder how accurate the other powders are in their database.
When it comes to trying your velocity to calculate barrel time. You do need a chronograph measurement for a specific powder charge that you loaded up. So as an example: if you have your specific gun and bullet and powder input into the software and you loaded up say 45 grains of varget in x-load... It will give you the estimated velocity in the top big box on the right. Now if you click on the obt button the very first screen will open up and it will use its calculated fps. So say the calculation is 2835 with that load, but you're seeing 2855 on your chronograph, then you can adjust it right there to allow it to help you calculate a more proper obt charge. I've also found that sometimes that suggested obt charge weight can still use a little tweaking. So if you put that suggested charge weight on your main screen, you can go up to the big box on the right, and the last two numbers in the left column of that box will be your "optimum" time and "actual" time (if I'm saying this correctly) this can still be fine tuned until those numbers are as close as possible. (I usually do this by adding or subtracting a tenth of a grain of charge weight at a time in the powder section). While paying close attention to the load capacity and safe working pressure.
A lot of times when I'm developing something new I'll find that some of the powders recommended in the charge weight recommended, aren't giving 100 percent or close to 100 percent powder burns. So I will have a tendency to play with different powders until I find a combination that gives me a good case fill (this is where your case dimensions and volumes are important) and a proper powder burn. I personally like to see as close to 100 percent burnt powder as possible. Keep in mind sometimes you can also adjust your seating depth to help massage these numbers. Without diving too deep in this post, I suspect that this is helping finetune your powder charge test and seating depth test simultaneously.
I've gone as far as putting all my chronograph numbers in a long with chamber pressure measurements (I have a pressure trace system that I use) and you can get very accurate refined load information. So I guess the long and short of it is put in as much proper information in as you can and you will receive more realistic data. Garbage in garbage out... There is a lot more in this software. I've added full wildcat cartridge and chamber dimensions but that's a whole other rabbit hole.
Hope this helps
Great info and I appreciate the well crafted reply. Case capacity is the first of the data point I worked with but diaming things in sounds tedious but worthwhile. Most load data is for bolt guns so I'll try to dial this in for my gas gun first.
I think you'll find that even without the gas leakage data that if you input your information and cross reference your chronograph data you'll still end up with most of the information you're looking for. I've been loading for my 308 AR-10 , and a few other gas guns in .223, .22arc, and 6gt with pretty spot on results.
