I have having trouble getting a good reading on the COL using the Hornady OAL gauge and the modified case. I followed the instructions and “firmly” press the bullet into the Lands, set the gauge’s set screw and them measured. I am getting a number. 089" more than the SAAMI numbers. I have measured twice.
This is my first time doing this and my first time using GRT. When putting these numbers into GRT I am getting super low pressure for being at max grains (I understand the math of why). So, does anyone have any insight into what I am doing wrong?
Your powder weight is pretty low compared to max. If you are seating your projectile further out than Saami, both these things will lower your peak pressure.
My 7mm-08 140gr Accubond handloads have a OAL of 2.858 and SAAMI is 2.800 which means I’m 58thou longer. Remember, SAAMI is the length to load to fit ALL rifles of your caliber, whereas as a hand loader you can find the loads that fit YOUR rifle.
As for GRT, recall the guy who built it died about 5 years ago and I don’t believe there has been much addition to it since then. With 7PRC being a newer cartridge, do you trust the data GRT provides? If so, remember, GRT is a starting point, not the end of your experiments.
You might want to look at min/max charges from reloading manuals, load up some rounds of various powder charges and chronograph the loads (running a ladder test of charges looking for signs of pressure). See if your velocities match GRT. I think Little Crow Gunworks hid all their YouTube content behind a Patreon or something like that, but Tim from LCG would tweak Initial Pressure in GRT to closer match the velocities of his rifle once he shot a ladder test.
So, I used the OAL gauge to find my max COAL for my rifle. That number is .089" longer than SAAMI. Its not where I am choosing to seat the bullet. I am just trying to learn if I made a mistake somewhere, somehow.
The pressure is based on Hornady’s Max grain for N565 (65.1). I put it a couple grains below max (64.9).
Man, I would not feel comfortable with that small amount of jump at all especially if I was a new reloader. Heck even now I’m not comfortable with that, my variation for seating depth is at least 0.005 sometimes even up to 0.007 which means it’s some bullets are going to absolutely stick and give you significant trouble.
You want to make sure you are consistent and accurate with your measurement. I got this for my 7mm PRC using the OAL gauge, a wooden dowel if the bullet got stuck and a 170 grain terminal ascent in the hornady dummy case.
I used the O.A.L gauge, measured 7 times and this is the average I got for my CBTO: 2.6710.
I followed the instruction from Panhandle Precision exactly. I feel 100% about this number.
I loaded a dummy round and set a bullet exactly at 2.6510 factoring a .020 jump. It chambers easily. did it twice no issues.
I am trying to use GRT to verify data, but when I put the COAL (3.3635) the pressure is way too low according to the book (N565). When I put in the CBTO as the cartridge length, I am way over pressure. So the tool is not helping me learn at this point.
Before I start loading, can someone confirm for me that so far, my process for getting my rifle’s CBTO is correct. I am asking because the factory Federal Eldx I have has CBTO that is .0455 shorter. I don’t know if that is significant, normal, dangerous…
Additionally, if someone has the time could you please tell me what numbers you enter for “Case Length”, “Cartridge Length”, and “Bullet Jump”? And how you got those numbers?
Case length is the length from the head of the case ( also sometimes referred to as base ) all the way to the mouth where the bullet would go.
Cartridge length goes from the head of the case all the way to the tip of the bullet when it’s seated
Bullet jump is the distance the bullet travels from when the primer ignites until it engraves in the lands and grooves. You don’t want the bullet touching the lands when it’s seated in the case, it needs to get up ahead of steam before it starts to engrave otherwise you get significant pressure problems.
Whether or not jump makes a difference is very dependent upon your bullet. The eldx is supposedly not very jump sensitive whereas many older bullet designs are. That is in terms of accuracy.
What’s your coal, and powder and powder charge? I will try entering it in quick load and seeing what I get. Also barrel length
For GRT, you have to use coal, not BTO. I’ve certainly found it to be a useful tool but it’s not the end all be all. I’ve had it tell me some things wouldn’t work at all and they’re some of my best hand loads. It’s always best to sort of look around and bounce things off of different places. If Hornady recommends a specific load, or VV, then I would be more tempted to trust them than anything else
