It’s hard to resist the temptation to spin the knobs when you have a nice group just outside where you want the bullets to be going.
During zeroing, I will adjust boldly on single shots and once I get pretty close to center (within an inch at 100) make my final adjustment (if needed), and then start shooting 5-round groups. I won’t make any adjustment to the zero until I have at least 2, and preferably at least 5 groups from which to determine the point that the centers of the groups are revolving around.
Glad that this has been useful to some folks here.
If anyone has any questions or wants clarification on anything, please feel free to post. I will reply as best I can, and add/edit the original post to consolidate everything.
Does the term “Average Mean Radius” seem redundant to anyone else?
The word “mean” is a more precise term for the common-use word “average”. Unless “mean” is being used as “not nice”, which makes no sense but at least isn’t redundant.
You could drop the word “Average” and “Mean Radius” would be just as descriptive… unless AMR is referring to a group of groups. In that case, it would probably be more descriptive if it was called Mean of Mean Radii. Or I guess… very mean radii.
I agree, just the initialization used by the Army, maybe MR got used somewhere else in someone’s definition list and they decided to err on the side of redundancy.
I stopped expecting them to make sense years ago…
ETA: looks like MR was taken to refer officially to Maintenance Ratio in an Inter-Service Memo.
So essentially, you are making 20 round groups, composed of 4 x 5 round strings (with each 5 round group being overlayed on top of the last, not re-centered to each group center). I can see how this is the best of both worlds…a statistically significant number of rounds fired, a comfortable number of shots per sting, as well as the ability of letting you see how the precision holds up during the progression of strings.
I’m all for this. I think it meets my personal preference for 10 round (minimum) groups and expands upon that in a useful way.
Since you have touched upon the topic of shift, can you give any pointers on minimizing cold bore and hot bore shift?
Great thread!
I too, would like to delve further into the Topic of POI Shift, especially concerning Zero’s and First Round Hit Probably. I had briefly read about Bryan Litz’s WEZ Analysis, but haven’t really finished it all yet.
I’m def. curious as to how an AR15/AR10 system stacks up against Bolt Guns such as AI/Sako TRG/M24/M40 etc. concerning Shift.
To nit-pick: I am talking about data based on not less than 20 rounds to track zero.
The zero is a living organism. It is born/hatched/sprouted only after careful incubation of information.
Recording data following that “feeds” the zero, keeping it alive and useful.
Since you have touched upon the topic of shift, can you give any pointers on minimizing cold bore and hot bore shift?
Once a barrel is broken in, I believe that most* cold bore shift is actually cold shooter shift.
With regard to minimizing shift at higher round-counts, another variable creeps in: mirage (more precisely: thermal turbulence).
As the barrel get heated up, it heats the air around the barrel/suppressor, causing it to rise. The difference in density between the hot air and colder ambient air causes the image of the target to shift and shimmer, making precise POA hold more difficult.
Of course, a hot barrel has different physical characteristics than an ambient temperature barrel, which further introduces variables.
The traditional approach to reduce this effect is to use a thick barrel, which heats up slower and more uniformly. The downside is that they also cool-off slower that a barrel with less mass. Various approaches, from increasing surface area to direct cooling, have been utilized to get the barrel back to ambient temperature more rapidly. The problem is that they still get hot (or at least significantly hotter). FWIW: most common approaches to increasing surface area to cool faster simply do not have enough area to bleed heat to air. Look at the heat sink on a CPU. Something similar, of larger scale, would need to be on a barrel to add enough surface area to significantly change the cooling attributes of a given barrel.
As a shooter, it is more important to me to know what the effect is, and when it starts to be a factor. Every gun is unique, and density of fire is an important variable.
“The zero is a living organism. It is born/hatched/sprouted only after careful incubation of information.
Recording data following that “feeds” the zero, keeping it alive and useful.”
Ain’t that the truth. And once you find the zero, and put it away, when you go back to look for it, it’s somewhere else much of the time.
And of course, the better the zero, the more you notice (as in, it “don’t shift much” on an iron-sighted AK).
F2S, very good discussion to open. The majority of the time I spend shooting, is from a bench or prone, shooting for groups and checking zeros, and re-friggin’-zeroing. It’s a learning curve I am still climbing after many years. The higher I scale this cliff, the foggier it gets, or so it seems sometimes! I do not expect to ever reach the summit and have the Guru reveal the meaning of life so that I can then know it all. I only hope to learn to climb better in each attempt.
It’s Info like what you provided FailureToStop that keeps me coming back to this website above anything else, Also really got me thinking about how I shoot and after reading it throughly I feel has made me a more well informed shooter. Keep up the good work man.
So when shooting from a standing position at 25 yards, what do you guys consider an acceptable pattern? When shooting 10 rounds from my 9 mm AR with 4x glass, I generally keep all 10 shots in a 3" circle and about 2/3 of those shots will be in a 2" group.
FYI, I run a 2.75 lb Elf trigger and a Lantec Compensator.
Here is a slow motion example at 25 Yards with the laser on shooting a 3" circles.
to echo “Outstanding”
Thought on the redundancy of Average Mean Radius; I’ll bet the Army really meant ‘radii’. As in the Average of a large set of Mean Radii measurements [from a large set of shot groups].
well, I sure as aitch expect better than 3" at 25 yds, standing unsupported, even from a pistol, much less a carbine. I might settle for 2" at 50 yds, given iron sights and old eyes, with a decent trigger job in a good AR, with good ammo. A lot of the cheap ammo won’t group a lot better than that, from the bench and with a scope, especially not from a .30 AK.
How much accuracy is enough is up to you and your skills. I want to be able reliably hit men’s heads at 200 yds, bipod and scoped, with my SBR if there’s no wind or mirage. Some people want to reliably hit crows or prairie dogs at that distance.
