Fast14riot
Gold $$ Contributor
That must have been you chatting with Charlie i saw in there this morning.
Gordens reloading tool vs Quickload
- Thread starter scasa
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Fast14riot
Gold $$ Contributor
I originally thought Initial Pressure was parametric to seating depth, but it actually tied to muzzle velocity. It's an editable field, change it to match your measured muzzle velocity. When selecting your bullet from the library, right click and select "new with copy" and you can change values to match your current lot of bullets. It will save in the GRT User tab of the library so you can use it next time.
QuickLoad's calculations are based on the volume of fired brass. Does anyone know if this GRT app uses the volumes for fired or sized brass?
I am guessing the GRT calculations are based on FL sized brass as when I compare numbers with my QuuickLoad they seem to only match up when I use the volumes for FL sized brass.
I am guessing the GRT calculations are based on FL sized brass as when I compare numbers with my QuuickLoad they seem to only match up when I use the volumes for FL sized brass.
Fast14riot
Gold $$ Contributor
Standard volumes are typically for sized. But you can easily add your corrected volume by clicking on the value and changing it.
GRT is based on CIP standards and the cartridge dimensions are assuming new factory ammo.
I believe the GRT manual calls for measuring volume in a fired case.
OK, thanks. I found what I was looking for in the GRT manual:
"Case Volume
This value represents the average case volume from a FIRED case , this value needs regularly to be
replaced by own measures of the reloader . Only, if measured correctly, GRT's simulations will
calculate accurate results."
Adam in WI
Practically lives here
Per their web page, Gordon has passed away. I wonder how that will affect the program going forward. I still debate buying QL, if nothing else for the more robust powder catalog.
As I understand it, as defaults, GRT uses assumed "standard" sizes based on CIP standards, and will generate results. But, those results will be more accurate for your loads if you measure the weight volume of your own fired cases and use those. Same for case length and some other input variables. I'm a new user and cannot say how much difference it makes, it just makes sense to measure your own to calibrate closer to what you are doing.
Also, in regard to Initial Pressure, in my first trial with Luger 9mm, I didn't know what I was doing. I posted on Discord and Charlie took my file and demonstrated calibration using the Optimum Barrel Time module, from which were extracted two parameters which updated my model. After that, the Initial Pressure was used to further tune velocities to better match my chrono data. I've subsequently done similar with 308 WIN and Wby 257 Mag.
I learned a lot from that, but came to a much better understanding after studying the manual on using OBT and watching one of the tutorial videos. I makes me wonder about tweeking Initial Pressure so much, just to get the numbers to closer, but that is the sort of thing that has to done often in models. Takes some time studying, understanding and learning to run complex models like these, not just a sit down to it and go.
In the GRT area of Discord, there is a long menu of information and discussions on the left side. Down quite a ways is the "How To" area, which is where the OBT tutorial stuff is.
Rick
Also, in regard to Initial Pressure, in my first trial with Luger 9mm, I didn't know what I was doing. I posted on Discord and Charlie took my file and demonstrated calibration using the Optimum Barrel Time module, from which were extracted two parameters which updated my model. After that, the Initial Pressure was used to further tune velocities to better match my chrono data. I've subsequently done similar with 308 WIN and Wby 257 Mag.
I learned a lot from that, but came to a much better understanding after studying the manual on using OBT and watching one of the tutorial videos. I makes me wonder about tweeking Initial Pressure so much, just to get the numbers to closer, but that is the sort of thing that has to done often in models. Takes some time studying, understanding and learning to run complex models like these, not just a sit down to it and go.
In the GRT area of Discord, there is a long menu of information and discussions on the left side. Down quite a ways is the "How To" area, which is where the OBT tutorial stuff is.
Rick
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divingin
Gold $$ Contributor
I heard (don't remember where), that Gordon's associates were going to try and keep his project running. Hope that's true.
jelenko
Gold $$ Contributor
Yes, it's posted on their Discord server.
The first thing they did was to extend the expiration date from this June to way out.
first... yes, i know, zombie thread.
next... i was going to post for any new info relating to 'start pressure' parameter as relates to seating depth, but found this thread.
finally... for a few of the folks i know to be GRT users, is not the parameter affected by bullets either touching, hard jammed, just off etc.?
(all the old reloading manuals caution to reduce loads as coal approaches touch, and indeed long throated chambers with legacy length bullets (the opposite condition) could run 'higher' pressures.)
since GRT does not seem to accommodate freebore length, how do we reconcile?
@Beiruty @jelenko @Straightshooter1
Murray Brook
Silver $$ Contributor
What I do for start pressure is calculate how far off the lands I am. Take 10,000 PSI and substract appx 145 PSI for every .005 I am off, then change the start pressure in GRT to match that #. Regardless how far off I am I never go below 3626 PSI. If I'm using a mag primer I don't go below 5221 PSI JMY
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jelenko
Gold $$ Contributor
Where/how did you get the rule of thumb to start at 10K psi and subtract 145 psi for each .001?
Thanks
Murray Brook
Silver $$ Contributor
I took the idea from QL where it says to start at appx 3626 and add 7200 if touching. Later after talking with guys that had pressure testing devices I was told that in their opinion that # was too high. The 145 PSI # came from an internet search on the subject. I then tried this over several months using QL and found the results to match known Vel readings after adjusting the BRF for that powder
Mistake in my last post I corrected. It .145 PSI for every .005, not .001
Mistake in my last post I corrected. It .145 PSI for every .005, not .001
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murray edited his post to 0.005" vs 0.001 increments.
thus, back calculating a linear relationship, likely?
0.247"/0.005" x 145 psi = 7163 psi
7163 psi + 3626 psi = 10,789
curious, was this in QL also? thanks
Murray Brook
Silver $$ Contributor
No This I got from GRT.
Murray Brook
Silver $$ Contributor
Reason I think that this works fairly well is after comunicating with a guy that has a pressure testing system he told me that the normal pressure signs--cratered primers, ejector marks, sticky bolt lift--show up when you are appx 5000 over max with a modern bolt action rifle using good brass. This seemed to be what QL was telling me. Only when I got to appx 69-70 KPSI in my 22/250 ( according to QL) did these signs show up.
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