7 RM 180 Hybrid Help

[IAHNTR]

I want to preface this post with I'm pretty new at this and this is the first time I've "worked up a load" for a LR rifle. I would like some opinions on where to go from here. Thanks

Here is my ladder test. Some of the higher charges I shot 2 rounds and averaged.
- Based on the Ladder I loaded up 6 rounds each at 68.0, 68.6 and 69.6 grains to see what they did for vertical dispersion. 2 targets only show 5 rounds cause I had to use 1 as a sighter.
- I used the Magnetospeed 3 for velocities and ES. I find it strange that the lowest ES gave me the greatest vertical spread.
- All rounds were seated 0.020 off lands.

 

[KYpatriot]

I think what you are seeing us one of the most frustrating aspects of load development, and that is the collision of small sample size and the science of statistics.

Looking at the load with the best vertical...was the ES caused by just one shot or were the velocities evenly distributed across the range?

No offense but at 555 it is very possible for the shooter to account for a little of the vertical, and if that isn't frustrating enough, you can induce errors opposite the error caused by the velocity which can really throw you off on your analysis. Don't forget wind effects, I'm guessing it is pretty flat in Iowa but here in ky I have seen some vertical wind effects from wind flowing upslope and down slope and of course there is a small vertical wind effect caused by the horizontal component of wind.

Finally, it's in the nature of random dispersion that even with the same load you shoot five consecutive five shot groups in a row with your rifle that you will likely get five different group sizes, and if you measured the extreme spread of the vertical in those groups at 555 yards it is very possible to get an inch and half or difference between groups with all the real world sources of error.

This is a long winded way of saying that there is no definitive answer to your question and the only way to truly get truth data is to keep shooting and collecting the cleanest possible vertical spread data by reducing the other forms of error as much as possible. Low wind days, low mirage days, good clean trigger pulls and natural point of aim and good parallax adjustment, all that stuff you probably already know.

I think you should just try again with those things in mind, shoot as clean as you can, and see what you get.
The reason I know other sources of error are present is that even a 40fps velocity spread for a 180hybrid at 555 yards is only worth about 1.8 inches of vertical. Maybe on that last group you shot really well and didn't add much error to the inherent precision the rifle is capable of combined with the environmentals that day.

The good news is that it appears you have an accurate rifle and are shooting pretty well, so I think you will sort this out. If it were me, I'd not worry about the chronograph so much and shoot that last load again.

Also, are you shooting these groups with the magnetospeed in place? If so, shoot without it and use the magnetospeed to find the velocity after you sort out what the rifle likes.

Finally for what it is worth I reduced my ES slightly by graphiting the necks to get a more consistent bullet release.

Frustrating process at times but the fact is as shooters we rely on ES and SD from a single 5 shot group as Truth when it is mathematical fact with a sample size that small that the real long term SD of that load could be as much as 2.5 times off that number. The only way to know with confidence that you got a sample from the middle of the bell curve is to shoot more.

 

[KYpatriot]

Also make very sure when using this method of load development that you are shooting a level rifle. You are trying to discern a very small vertical component of group size and any cant in your elevation adjustment will muddy it up.
Also, you may want to blow up the size of these groups so you can " zoom in " on the vertical caused by velocity variation by shooting a farther distance. The 7rm and berger 180 hybrid is a very high performance LR round combo that minimizes these errors so you may need to get out 800 to 1000 to discern these velocity errors more easily. The caveat Of course is at those ranges it is even more important to pick a good day to minimize environmental influences like wind or mirage.

 

[IAHNTR]

Thanks KYpatriot. I know these are very small sample sizes, but you gotta start somewhere.

Yes, these groups were shot using the magnetospeed attached to the barrel. I wanted to see what I was getting and next time I won't use it. At least now I know what speeds I'm getting and can dope accordingly.

I do use the Imperial dry lube with their application media. It was kinda windy that day with 5-8 mph from the 4 o'clock. I will double check that my rifle level is level when my reticle is plumb.

I completely understand that my skills (or lack of) and inherent environmental factors all contribute to where the shots print.

What do you think of loading up 10 each of 69.4, 69.6 and 69.8 and shooting these again at 800ish? Would different seating depths play enough of a role that I should be looking into that aspect first?

 

[KYpatriot]

I think that would be fine if you can get a good wind day. Different seating depths can change things a lot during a load work up but I would use that to fine tune a load. The 180 hybrid is less sensitive to seating depth than the vld types which is good.

I have run into the exact same problem you have and learned to trust my groups at range more than the chronograph. I don't put as much emphasis on those numbers as I used to and instead focus more on the real world results of groups at range. I found that the vertical I was actually getting was not what the chrony would suggest.
I'd shoot the fastest load first, and if it groups well two more times then I'd stick with it, and if not investigate those other loads.
In truth, load development never really ends. I record my shots and results and over time you can get a better feel for what is actually going on and when you get it totally figured out it is time to replace the barrel lol.
Since I'm not a benchrest guy, and the inherent accuracy of the rifle/load is usually not the limiting factor on a long range hunting or tactical shot in the field, I cease load development when I get something "good enough" and spend more time practicing those things that have a greater impact on the success of a shot in the field...namely building a good consistent position give a good trigger break in field conditions and doping the wind. I am, like a lot of long range shooters, somewhat anal retentive which you have to be to have the discipline of do this, but you can spend too much time finding her perfect load at the expense of competing priorities. So I force myself to quit when I find something around 1/2 moa and spend my time practicing those things that actually cause me to miss...and it usually ain't the rifle lol.

 

[IAHNTR]

Sounds good KY. I have to load the rounds with powder anyway. I have not shot these loads at 100, so I don't know how they group there. My thinking was to find the nodes in the ladder then pick the middle charges in the nodes and shoot those to determine least vertical spread then go back to 100 and play with seating depth to fine tune. From my research this "should" work, but being this is my first time doing this, lots of questions pop up.
Thanks for taking the time to respond.

 

[KYpatriot]

Your welcome looks like you are well on your way!!