Gordon's Reloading Tool

[Jim Poulette]

I just started using this, mostly to compare some of the chrono data I've accumulated with potential GRT results. Generally I like the interface.

One hitch: I know the physical difference between "barrel length" and "projectile path" - but does anyone know what exactly the relationship is in this software?

Example - using my 629, with a 2.625" barrel, if I enter 2.625" as the barrel length I lose about 100-150 fps of velocity and the results do not agree with my measurements.

If I change the barrel length to an arbitrary dimension that changes the projectile path to 2.625" - the numbers match almost perfectly. (Only the barrel length is a variable in GRT - the projectile path is derived)

I will post to Discord - but I was wondering if anyone has experience with this. Simple solution I suspect is to make a custom database item (".44 mag, 629, w/2.625", or something like that) so maybe that's the answer. Or maybe there's a software 'switch' somewhere I don't know about.

Entries on the left is a good match to my chrono data - entries on the right are WAY off. This mismatch is present in the 4 separate data sets I've attempted.

 

[pastera]

Likely from the difference in how you measure barrel length between revolvers and other guns - I'm assuming you added ~1.6" to the barrel length to get to the correct projectile path.on

Didn't look closely at your pictures - the difference looks like COAL - Bullet Length which is easily explained by my first assumption but corrected by some actual brain involvement on a second read.

 

[Jim Poulette]

Yes - I think you have it !

OK - from the GordonsReloading group on Discord:

"For revolvers, barrel length includes the cylinder length, enter the total length from the recoil plate to the muzzle. The user will need to adjust for the gas loss at the cylinder gap. Rifle barrel lengths are measured the same, only they do not have cylinder gaps. In rifles "recoil plate" is the bolt or breech block face."

I will give it a try and post the results.

 

[Jim Poulette]

Sometimes you can't help but "step in it".

So the measurement on the 629 (recoil plate to muzzle) is 4.320", gap location is defined as 1.595 (position "x") and .006" (width "w").

Calculated muzzle velocity is 886.5 fps, against a measured (10' from muzzle) mean of 900 fps, and median of 889.0 fps (18 shots). At an estimated loss of 2.4 fps/ft over 10 feet - that gives you 900 - 24 = 876 fps calculated.

So, all in all - not too shabby. The calculated velocity is within 1.1% of measured. I'm definitely sold - let's move on.

 

[Jim Poulette]

Beautiful morning to test a few more .44 mag loads with the 329PD (4" barrel).

The measured velocities are coming remarkably close to the GRT calculated results when the propellant chosen is N320. Outliers have not been removed. Since there is no approved GRT Alliant SP option, this is the closest data match that I could find in their propellant library. I'll be close to the 8.6 gn. max soon.

Now, time for yard work chores !