Bad SD and ES but good group...
- Thread starter RTTY
- Start date
Variances in velocity shows exponentially worse groups, the greater the distance. You may not notice vertical strings at 100m at all.
How many shots in your groups? Too small of a data set gets weird results that misinform.
How many shots in your groups? Too small of a data set gets weird results that misinform.
Last edited:
That's not strange at all...There's absolutely zero relationship between SD/ES and group size at 100m....There is a relationship between them at 800m+ for 6mm and 6.5mm short action cartridges. The greater the SD/ES, the higher the vertical dispersion, all other things equal.
If you're drawing conclusions about your muzzle velocity's consistency for a given load recipe or charge weight at a production lot level using less than 30-40 rounds worth of MV data in your sample, you're wasting your time.
Focus on fine-tuning the group size at 100m then once you have something w/potential, load up 30-50 rounds of that exact recipe, shoot at known distances out to 1000-1200m or so and record MV data as well as drop data. Correct your BC per drop figures vs predicted by your ballistic software and record that along with all the relevant environmental data. Then assess your load's performance against your expectations/requirements and see if they align.
Believe the paper. Better yet, put the paper out at 500 yards
Hello,
@38,4gn have 5 shoots.
@38,7gn and up 4 shoots for group.
Can you explain me better your commenti?:
"Variances in velocity shows exponentially worse groups, the greater the distance. You may not notice vertical strings at 100m at all."
Thanks for the reply!
So, for distances from 500m and above, do you recommend that I work on a load that on the chronograph shows lower/lower/better SD and ES values, looking for the best group on paper?
Hello, your advice for me are working with consistency velocityes at 500m and up?
If you want the best load that shoots at distance, shoot it at distance and actually see.
I dont trust pure numbers because too often I have found that the best group in the real world results don’t have the best chrono numbers.
And you have a great avatar.
I have been reading and seeing elswhere where the stats aren't that sweet but the performance is acceptable.
Let's say your ES is 50 fps on 6.5CM 140ELD-M (I have this handy so good example). Let's say your high is 2850fps with absolute drop of 2.2"@100yds and 317.5"@1000YDS. Your low is 2800fps with absolute drop of 2.3"@100yds and 330.2"@1000YDS.
Your ES will add 0.1" to the vertical spread at 100yds and 12.7" at 1000yds.
Differences in velocity get far more noticeable at distance. A vertical string is a group that is narrow side to side, but tall top to bottom, caused by high ES.
On number of shots per group, let's say every time you shoot you have a 50/50 chance of shooting right or left of aim. Like flipping a coin.
If you test 20 five shot groups, you flip the coin 100 times.
If you flip a coin 100 times, is is almost guaranteed that at some point you will get 6 heads or tails in a row . If you look at a group where every shot went left or right, that group will be tiny compared to the others. Was it probability or the load?
Really is that with small numbers of rounds per group, the results are suspicious at best.
I use 5 shot groups to find a NODE with good SD ES. Then do 10 shot groups in the node on paper for size. Then 15 shot groups under different range conditions to decide if it is consistent.
If a 5 shot groups is great, but before and after are poor, don't get excited. If you get a bunch of good groups and the one in the middle isn't the best, retest that range you are getting close.
If you test 20 five shot groups, you flip the coin 100 times.
If you flip a coin 100 times, is is almost guaranteed that at some point you will get 6 heads or tails in a row . If you look at a group where every shot went left or right, that group will be tiny compared to the others. Was it probability or the load?
Really is that with small numbers of rounds per group, the results are suspicious at best.
I use 5 shot groups to find a NODE with good SD ES. Then do 10 shot groups in the node on paper for size. Then 15 shot groups under different range conditions to decide if it is consistent.
If a 5 shot groups is great, but before and after are poor, don't get excited. If you get a bunch of good groups and the one in the middle isn't the best, retest that range you are getting close.
Last edited:
I'll follow your advice.
But are you telling me to develop around the groups with the best SD and ES?
Well, so I choose the group with better consistency and see what it gives me in the long distance
Most of the time (within reason) you won't notice the effects of velocity variation until at least 400yd. Usually more like 600-800 is when you start to see it meaningfully.
Best group on paper at 100m, then refine your production process to reduce SD/ES. Things like 100% consistency in powder drops, minimal as possible seating force on your bullets, consistent primer seating depth, quality materials and components (i.e. don't expect single digit SDs out of el-cheapo brass) and so forth.
Chances are there is a range of charge weights that will provide you the precision and velocity you want where you can refine your reloading process to get SD/ES down to where it needs to be...High single digits to low double digits across an entire prod lot of 200 rounds should give you acceptably tight vertical dispersion out to the max effective range of your rifle (or however far your typical max engagement distance is).
Yep - my experience as well...I have high teens/low 20s SD for my clone of Mk 262 Mod 1 and i dont start seeing material vertical stringing out of my Mk 12 Mod 1 until I'm shooting past 800m which is relatively rare...
First off . . . none of those SD's or ES's are "bad". Some better than others, BUT. . . .it just too small a sample size to draw any conclusions. When you first shoot a ladder like you did and see which are the best numbers, you've got to shoot that ladder again, or shoot the one load at least again to see if will confirm what you saw to start with. And if you're going to do a confirmation test of a load, you're need to do 10 or 20 rounds to better see what you're ES is more likely to be expected.
I rely on my chrono data to tell me how well I'm loading my cartridges. And those numbers suggest to me like your doing a good job of reloading. The best SD's or ES's don't always corelate to the best results on target. That's where you've got to focus on the target results to determine which load to use. Since you're getting good chrono numbers, you should then simply focus on your targets and make your decision accordingly.
The the velocities your record can be very important when finally putting together your dope for shooting long range. . . like for ELR shooting.
One of the things I remember out of the infamous Houston Warehouse is that you don't see elevation changes on target at 100 yards until you get over 100 FPS in velocity delta.
You aren't really going to see big ES spreads show up on target unless you are shooting at distance as mentioned above, or your ES gets into pretty extreme ranges.
I also wouldn't read too much into a sample size of one group per charge weight.
You aren't really going to see big ES spreads show up on target unless you are shooting at distance as mentioned above, or your ES gets into pretty extreme ranges.
I also wouldn't read too much into a sample size of one group per charge weight.
I have also read from others and even in the instructions for ballistic apps that truing the profile is best done at longer distances. A minimum of 200 yards but then, farther is better, if possible. At least for target shooting.
You develop based on group size and target velocity FIRST!
You have absolutely no idea how consistent a given sample charge weight will yield at a production level with 3-5 shot groups! You won't know how consistent that recipe will be until you put the load recipe into low rate initial production...That's when you load up 50-100 rounds or so, go out to the shooting spot/range and gather SD/ES over that entire sample of 50-100 rounds.
I usually shoot 50-80 rounds and assess my SD/ES and revisit my reloading process, tweaking it if I don't like what I see MV consistency-wise.
Thanks for your advice.
On my 6,5x47 Lapua I use only the best componente on the market.
I look for long range loads so I test 39gn for 500m and up...
Thanks
???
Seem to me your reloading procedure is pretty good to me to get those numbers you've shown in the OP.
I'm happy with it; I learned a lot of what I put into this by reading the discussions on this forum.
I was going to ask you what dose I should focus on, the 39gn?
You can't make that determination from just one group per charge weight.
I wouldn't focus on any of them until I ran a second ladder tests of the same charges to see which might actually be repeatable.
Similar threads
