Loaded some shells for my 7 rem mag. Loaded 3 shells in each group, increasing charge by .3 grains. Shots were at 200 yards. Had one load that had an sd of 0 and two with 4.04. Unfortunately these loads weren't close to one another. Load with 0 sd had one of the lowest vertical spreads but the group stunk. Had one group that shows a .9" group at 200 with a lowers vertical spread but the sd is almost 25. I don't see a clear path here. Any suggestions? I can load targets but there are 10 separate targets so I loaded the data instead.
7mm load development
- Thread starter Rhunter2
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WeiserBucks
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Bullet? Powder ?
jpd676
Well-Known Member
I would test your loads at distance. Sometimes your loads will suprise you way out there.
Is your barrel new and broken in?
Is your barrel new and broken in?
H1000 - eldx 162
Barrel is broken in.
Just some possibilities to consider.
1) You might not be stabilizing that bullet, depending on the twist rate of your barrel and the elevation where you're shooting. Assuming a twist of 9.25 (my rifle), sea level, and velocity of 3,100 fps, I calculate a gyroscopic factor of 1.416 (i.e., less than 1.5).
2) Was your barrel excessively hot as you progressed through the test? Depends how quickly you fired and how heavy your barrel. One of mine can only go about 10 rounds before it needs a full cool-down, or groups are affected.
3) Does your scope have an adjustable parallax (and was it properly adjusted to 200 yards)? I'm reaching here.
1) You might not be stabilizing that bullet, depending on the twist rate of your barrel and the elevation where you're shooting. Assuming a twist of 9.25 (my rifle), sea level, and velocity of 3,100 fps, I calculate a gyroscopic factor of 1.416 (i.e., less than 1.5).
2) Was your barrel excessively hot as you progressed through the test? Depends how quickly you fired and how heavy your barrel. One of mine can only go about 10 rounds before it needs a full cool-down, or groups are affected.
3) Does your scope have an adjustable parallax (and was it properly adjusted to 200 yards)? I'm reaching here.
One more.
4) Your last 4 groups, or so, might be bucking up against pressure issues, fouling them up. I know in my 7mmRM with H1000, those would be bumping up against pressure issues, plus your velocities start to get wonky at that point. So you might want to remove some/all of those from the mix of consideration. Still doesn't answer the question.
4) Your last 4 groups, or so, might be bucking up against pressure issues, fouling them up. I know in my 7mmRM with H1000, those would be bumping up against pressure issues, plus your velocities start to get wonky at that point. So you might want to remove some/all of those from the mix of consideration. Still doesn't answer the question.
My twist is 9.5. According to Hornady, that is optimal. Not sure how I test that. I spent about 3 hours in 20 degree temperatures firing 30 shots. The barrel was warm at most. I shot pretty slow. Barrel was completely cooled every 6 shots. Scope does have parallax that was set at 200.
Not sure what you mean by that. The only pressure charge in the last four that really confuses me is 69.1. Not sure why that one had such high velocity.
I might be wrong on the bullet length. Is it 1.478"? Pulled that from online.
With bullet length, caliber, bullet weight, barrel twist, velocity, and elevation you can calculate the gyroscopic factor. If you search for "twist calculator" online, you'll find one. I've got it in Excel and my result at sea level (don't know your elevation) is 1.342 with a 9.5 twist at 3,100 fps. Generally I think 1.5 is considered optimal, though others may disagree.
With bullet length, caliber, bullet weight, barrel twist, velocity, and elevation you can calculate the gyroscopic factor. If you search for "twist calculator" online, you'll find one. I've got it in Excel and my result at sea level (don't know your elevation) is 1.342 with a 9.5 twist at 3,100 fps. Generally I think 1.5 is considered optimal, though others may disagree.
Another (possible) way to interpret your average velocities:
- I expect the average velocity to increase fairly consistently as the charge is increased consistently,
- In your data, I only see that happening for the first 3 or 4 groups, then it basically levels off, with odd (pressure) results for 69.1 and 70.0.
- You could potentially be hitting pressure issues (velocity leveling) as early as 68.5 or 68.8.
Maybe.
Edit: It's likely not a stability issue. Your question inspired me to read up on the revised stability formula that takes into account bullets with plastic tips (which your bullet has). Though I don't know the length of your ballistic tip, it's most certainly long enough that it would achieve a stability factor of 1.5+.
If you wanted to see this for yourself, check out two different online twist calculators. The one on the Berger website does NOT take into account the plastic tip, and results in a stability factor lower than 1.5. The one on the JBM Ballistics website DOES take into account the tip, and shows a stability factor greater than 1.5.
So basically, nevermind (re twist/stability).
If you wanted to see this for yourself, check out two different online twist calculators. The one on the Berger website does NOT take into account the plastic tip, and results in a stability factor lower than 1.5. The one on the JBM Ballistics website DOES take into account the tip, and shows a stability factor greater than 1.5.
So basically, nevermind (re twist/stability).
epoletna
Well-Known Member
I admit to being skeptical of the value of 3-shot groups. I haven't discussed this with a lot of accuracy nuts, but one friend who is pretty much an accuracy nut is satisfied with 3 shots while another insists on 5-shot groups to establish a useful baseline. I tend toward the latter. I wonder, if you were to load up five rounds each of 67.6, 67.9 and 68.2, would you collect a more instructive data set? At the very least, you would see if there is a random shot that creeps in somewhere.
The best method I have found is the OCW (optimal charge weight) method for my 7mm Rem Mag, and all other calibers. It was started by Dan Newberry years ago. What you are doing is similar, except I shoot round robin like Dan does, and 100 yards is just fine. Two minutes between shots, and take a few fouling shots before you begin. I usually use 5 to 6 different charges, hence 5 - 6 targets. I also use QuickLOAD and a LabRadar. This way I can document everything I need accurately, especially the true burn rate of my H1000 at a given temperature while at the range. I don't get hung up on extreme spread and standard deviation anymore, and just go with what I see on target. You will find your optimal charge weight, it just takes time.
