Help deciphering my data

[HMRamateur]

I am currently working on a load for my Bergara HMR pro with the 139 gr lapua scenar in 6.5 CM. I am using hornady brass, all virgin up to this point now, federal 210M primers, and hodgdon 4350.

I started with a ladder test, starting at 40.0 grains of powder, working my way up by 0.2 grains at a time, as shown in the first picture.

The following picture shows the charge weights I shot, using the same seating depth of 2.310 to ogive. I was having issues with my labradar at this point, so that is why there is no data.

While I know the possibility of a low ES is because I don't have a full 5 shot group, I decided to go with 40.9 grains as my charge weight, and begin seating tests at 0.03 intervals.





Since the charge weight is the same, yet I am seeing a different ES for each 5 shot group, is that just indicative of the actual ES for that charge weight over a large enough sample, or does it change because of seating depth and different pressures? If just going off speeds, group 3, at 2.301 to ogive is producing the best results. Group 5, at 2.295 to ogive produced the worst ES, yet produced the best looking group on paper.


Group 3 was still promising, as the first shot felt good, but the sights did not end up even close to the point of aim after my follow through, so that could explain why that group is larger.


So, am I really just seeing a larger ES overall as a result of a larger sample (over 35 shots), or is this a result of changing pressures because of seating depth, and while that group I shot looks really good, it isn't an ideal ES. I could shoot both seating depths and take speeds again now that all the brass is fire formed, but I am hoping for a little knowledge that could save me from more testing that might not be necessary (Or is more testing at different charge weights what is really needed).

 

[Doom]

You may find this thread helpful. Trying to compare those SDs is a waste of time and effort. The chronograph is +/- 2.7 fps at best.

Stats for velocities and groups.

So why is a 5 shot the standard for groups but not for velocity? I’ve been seeing a lot of discussions lately about SD numbers being useless without a large sample size. I agree that the SD may be unreliable with a smaller sample size but I don’t think it is completely worthless. I use the 5...

www.snipershide.com

 

[nn8734]

I and many others have been repeating this incessantly about ES and small samples: it’s worthless. 5 shots is totally insufficient as a sample size from which to draw any conclusions so it really shouldn’t be a apart of your decision making this early in the process. Also, there isn’t any relationship between group size on target and SD/ES figures, don’t fall into that trap.

Your groups look ok, you can further tune/tighten with additional seating depth trials at smaller increments if you like the velocity at that charge weight. I’d be curious as to how the POI center of the adjacent charge weights at 40.6 and 41.3 looked compared to the POI center at 40.9. That would prob be the only test I’d conduct as I’d want to confirm/deny stability before seating depth trials.

ETA: once you think you have a final recipe, load 30-40 rounds and fire them over LabRadar or your chrono on a KD range, recording your actual drops at 100m distances. Then look at the SD/ES of that entire string. Whatever those figures are will be indicative of how that entire production lot will do (lot=~500 rounds or so). Periodically gather data as environmental/seasonal changes occur, tweaking it if necessary.

 

[HMRamateur]

You may find this thread helpful. Trying to compare those SDs is a waste of time and effort. The chronograph is +/- 2.7 fps at best.

Stats for velocities and groups.

So why is a 5 shot the standard for groups but not for velocity? I’ve been seeing a lot of discussions lately about SD numbers being useless without a large sample size. I agree that the SD may be unreliable with a smaller sample size but I don’t think it is completely worthless. I use the 5...

www.snipershide.com

Thanks for the link to that thread.

I and many others have been repeating this incessantly about ES and small samples: it’s worthless. 5 shots is totally insufficient as a sample size from which to draw any conclusions so it really shouldn’t be a apart of your decision making this early in the process. Also, there isn’t any relationship between group size on target and SD/ES figures, don’t fall into that trap.

Your groups look ok, you can further tune/tighten with additional seating depth trials at smaller increments if you like the velocity at that charge weight. I’d be curious as to how the POI center of the adjacent charge weights at 40.6 and 41.3 looked compared to the POI center at 40.9. That would prob be the only test I’d conduct as I’d want to confirm/deny stability before seating depth trials.

ETA: once you think you have a final recipe, load 30-40 rounds and fire them over LabRadar or your chrono on a KD range, recording your actual drops at 100m distances. Then look at the SD/ES of that entire string. Whatever those figures are will be indicative of how that entire production lot will do (lot=~500 rounds or so). Periodically gather data as environmental/seasonal changes occur, tweaking it if necessary.

When you say you want to compare POI centers for stability, are you looking for pretty much the same POI center between those charge weights?

I must have foolishly tossed the other pages because the group sizes were too large.

 

[nn8734]

Yep. I like to see a pattern across three consecutive charge weight increments assuming a .3-.4g spacing between each. If you don’t have any pics, I’d maybe re-run at 40.6, 40.9 and 41.3 using three-five shot groups. Three to five shots per group are sufficient as long as you don’t induce any shooter error into any of them.

You’re just looking for POI pattern consistency, don’t pay attention to group size or SD/ES. If the pattern holds up, I’d start playing with seating depths to see how tight you can get the groups…

 

[HMRamateur]

Yep. I like to see a pattern across three consecutive charge weight increments assuming a .3-.4g spacing between each. If you don’t have any pics, I’d maybe re-run at 40.6, 40.9 and 41.3 using three-five shot groups. Three to five shots per group are sufficient as long as you don’t induce any shooter error into any of them.

You’re just looking for POI pattern consistency, don’t pay attention to group size or SD/ES. If the pattern holds up, I’d start playing with seating depths to see how tight you can get the groups…

Thanks for the info! If you find a consistent pattern do you choose the middle charge weight?

 

[nn8734]

Thanks for the info! If you find a consistent pattern do you choose the middle charge weight?

I make that decision based on the ambient temp, which is largely driven by the season, at the time the load is developed. If in summer I pick the top charge weight (I’m assuming there’s no pressure signs), reasonably expecting it will remain stable in the winter. Vise versa in the winter. I go with a charge weight towards the middle in spring time if temps/DA is in the middle of what I typically see.

The wider the node for POI stability the less sensitive your ammo will be to seasonal changes in temp.