243Win GRT pressure predictions vs Book Data

Nimbus73

FNG
Joined
Nov 19, 2024
Messages
16
Location
SW Louisiana
I'm asking for a little help to understand. I have loaded but not shot yet a short ladder using the 105gr Match Burner and H4350 in my 243Win. I want to see if it will stabilize. I made 10 rounds, 2ea at .3gr intervals. My intentions were to shoot 5 at 100yds and 5 and 200yds to see if I have any tumble or key holing. I recently downloaded GRT, trying to learn it and I've been comparing some of my other shooting results to its predictions and for the most part I'm impressed. This is my concern. I used Barnes load data for my source and started in the upper third of their load range at 41.3gr H4350 thinking I would be well under max pressure and ending with 42.5gr being .3 grains over their max, but when I entered the data into GRT for my loads it tells me I'm way over pressure. GRT predicts 40.7gr to be about 59.7kpsi and 42.2gr at 67kpsi and 42.5 up to 68.6kpsi. How much faith should be given to the pressure predictions GRT puts out? Is the Barnes data too spicy? I've loaded 100gr Sierra SBT's up to 42.5gr seeking more velocity from my 20" barrel before I realized I'm pushing way too hard and have backed off to 40.3 gr. If GRT is even remotely close for this recipe, I need to pull these rounds and find a safer ladder. What have your charges been for this or similar 105gr projectiles in 243Win. and what are your experiences?
 

Attachments

  • Screenshot 2025-06-06 162518.png
    Screenshot 2025-06-06 162518.png
    125.5 KB · Views: 11
  • Screenshot 2025-06-06 162621.png
    Screenshot 2025-06-06 162621.png
    925.4 KB · Views: 11
That’s a cool program - I hadn’t heard of it before. It looks like a great way to explore loads that manuals don’t cover.

Printed manuals and programs like GRT or Quick Loads are just for getting a good starting point and none of them exactly know what your rifle and reloading components will do. Every source of information suggests starting low and working up. I have no problem exceeding max loads a bit if they still give long case life (10 reloads) and acceptable case head expansion (5 cases tracked individually until failure), and also have no problem stopping before max if pressures dictate. Max loads judged this way takes a lot of shooting and trips to the range, but it has produced reliable, safe loads with good velocity without ever blowing a primer or causing problems.

From the GRT faqs:

IMG_0650.png
 
I tend to feel its pressure vs velocity (in your barrel length) prediction is probably fairly realistic, you just have to test what powder charge that requires with your components and it may be a grain (or more) higher or lower due to lot variations and such.

The programs rely on making sure case capacity and COAL are dialed in. Once you shoot some loads and go correlate it with GRT, from there it tends to spit out more accurate info in adjustments you make. Its good for predictions and reviewing different combos but the ultimate powder charge vs velocity is going to depend on your components.
 
You dont know the case volume that was used for the barnes manual. Or the impact of how fast/slow the lot of powder you have vs

This should answer the question from the OP - Barnes data probably isn't "Spicy" for the brass/bullet /powder lots, barrel, chamber, etc that they used to get it. What assumptions GRT is using and what your components and rifle produce are relatively unknown based on the post.

So shoot em and let the results speak.
 
Back
Top