Shooters Forum banner
81 - 99 of 99 Posts

·
The Hog Whisperer (Administrator)
Joined
·
37,408 Posts
Interesting, Nick, thanks. I may have to overlay those two graphs on each other if the charge increments are the same.... never thought of that.
 

·
Registered
Joined
·
79 Posts
groups are more important than velocities, until you get radically slow.
The problem with a Magneto-speed is that it hangs on the end of the barrel, therefore, introduces a variation in the barrel-vibration.
Have fun,
Gene
 

·
Registered
Joined
·
259 Posts
Discussion Starter · #83 ·
groups are more important than velocities, until you get radically slow.
The problem with a Magneto-speed is that it hangs on the end of the barrel, therefore, introduces a variation in the barrel-vibration.
Have fun,
Gene
The reason it is only used to gather speed numbers and not accuracy.
 
  • Like
Reactions: Popeye212

·
Registered
Joined
·
4,859 Posts
Variations in velocities cause vertical stringing at long range with centerfires, a shooter is unaware of it if the groups are shot at 100yds. For a hunting gun where few shots are taken past 300yds probably doesn't matter.
I shoot alot of 22lr, excessive variations in velocities with all but the best 22 ammunition is common and it results in significant stringing at 100yds where lots of rimfire games have targets now. Lots of 22 ammunition groups great at 50yds, significantly less at 100yds.
I've never shot the centerfire 1000yd games but can imagine it is the same. Where I noticed it first many years ago was prairie dog hunting, I had a 22-250 that was difficult to hit a dog laying across the top of the mound or feeding in the grass, one shot would go high the next would be low sending them down the hole, I noticed I could hit them much more often if they were standing even though they presented a much smaller target.
If you don't like or don't have a chronograph shoot your groups at the farthest distance you plan to shoot at, extrapolation of group sizes from 100yds to 300yds or beyond won't give you an accurate estimation of the accuracy of your gun at long range.
Herein lies the problem with shooting groups at long range, many hunting guns don't have scopes on them capable of getting a good group at long range, they lack the power and therefore the target resolution, they may not have an adjustable objective to get the parallax out either. Then there's the wind and mirage, huge factors on all but the best days in many parts of the country.
 

·
Registered
Joined
·
79 Posts
KMW, so true.
I got lucky (a looong time ago) and use an Oehler M33. I do both, at the same time. Neither effects the other.
When I get into "information overload" I just write it into my log book, and think about it later.
Have fun,
Gene
 

·
Super Moderator
Joined
·
13,751 Posts
In a similar discussion on another board, this link was posted to an article that goes over the principles pretty well as illustrated by testing commercial 6.5CR match ammo. It gives you a pretty good idea of what matters and how much, though it is a pretty lengthy read.
 

·
Registered
Joined
·
4,859 Posts
One thing that's seldom discussed on forums is the real truth nearly all of us seldom make the perfect shots under field conditions, it's pretty easy to be off 3-4" on a shot at 300yds plus from where you meant to break the shot, add to that the group size with a little vertical stringing thrown in and you have one of those unexplained missed shots or worse a wounded animal. Your pet rifle and load that grouped under an inch at 100yds can place a bullet 8" high or low from where you wanted it to be.
 

·
Registered
Joined
·
4,859 Posts
I was scanning through here and noticed Doom had addressed me specifically on page 4 post #66, I totally agree that the sample size I shot is to small and under "normal" conditions I would have gathered a much bigger sample but components are very difficult and expensive to obtain in 2021. I found one box of 87gr V-maxes on gunbroker{43.00} and a kind person on this forum sold me a partial box. A friend recently picked up a pound of lever revolution for me on a road trip across the country over 1,000 miles away. A week ago I bought two pounds of powder on gunbroker and paid 96. with shipping. At least for me these are not the times to be sending hundreds of rounds downrange to accumulate data. No doubt the numbers I've posted for my new 6mm arc are less than perfect but until things change they'll have to be good enough.
 

·
Super Moderator
Joined
·
13,751 Posts
It's not that small samples are bad or good. Just that one needs to be aware of the limits of what they are telling you. Sometimes, they are more than enough. Here's an example:

Suppose you hunt Whitetails in Eastern woods, and you know that the maximum clear shot range is going to be 125 yards in your hunting grounds. You also know there is about a 10-inch diameter kill zone on the deer. You also know your field hold position ability is about a 4-inch circle in one hundred yards, or likely a little over a 5-inch circle at 125 yards (estimated at 5.07 inches by Litz's TOF difference criteria; we'll call it 5.1 inches). So, how well does the gun have to shoot a single 2-shot or 3-shot, or even 10-shot group at 100 yards to give you, say, 95% confidence you will stay in that 10-inch circle at 125-yards in the field?

The first thing is to realize is that your 5.1" 125-yard hold circle has an area of 20.43 in². The 10-inch circle has an area of 78.54 in². The difference is 58.11 in², which is the area of a circle 8.60 inches in diameter. At 100 yards, that circle will reduce to a 6.75-inch diameter circle. So it would be best if you had 95% confidence your rifle would stay inside a 6.75-inch circle when fired from a machine rest at 100 yards. You probably don't have a machine rest, but if you can match the machine rest required numbers from the bench, despite adding a little human imperfection to the hold, then you are good to go with a little extra safety margin.

Crunching the stats, 95% confidence of staying inside a 6.75-inch circle at 100 yards works out to mean a single 2-shot group can be no wider than 1.51 inches, a 3-shot group no wider than 2.74 inches, a 5-shot group no wider than 4.40 inches, and a 10-shot group no wider than 5.48 inches. The number gets bigger as the sample size grows because you are increasing the probability you are seeing a realistic example of your gun's precision, thereby lessening the need to hedge the diameter to keep 95% confidence you will stay inside your 6.75-inch 100-yard circle. Below is a table with shots per test group on the left and the allowable diameter multiplier on the right for 95% confidence (in this case, you would multiply that multiplier by 6.75 inches to get the allowed size from your group sample size or shot count).

In practical terms, the above would need to be fired in the same conditions (temperature, in particular) you expect in the field. You could shoot two (make sure your barrel condition is the same as you will have in the field), and if their separation exceeded 1.51 inches, as it randomly may, but it does not exceed 2.74 inches, you could fire a third to see if it also stayed inside, thus meeting the 3-shot criterion. But if the first two were, say, 5 inches apart, you would have to fire five more into the group for a total of 7, seeing that all 7 stayed inside 5.03 inches (the limit for a 7-shot group from the multiplier below times 6.75 inches).

Single Test Group Shot Count 95% Confidence Multiplier Deer Example
2​
0.22​
1.51 in​
3​
0.41​
2.74 in​
4​
0.56​
3.81 in​
5​
0.65​
4.40 in​
6​
0.71​
4.77 in​
7​
0.75​
5.03 in​
8​
0.77​
5.22 in​
9​
0.79​
5.36 in​
10​
0.81​
5.48 in​
11​
0.83​
5.57 in​
12​
0.84​
5.65 in​
13​
0.85​
5.72 in​
14​
0.86​
5.77 in​
15​
0.86​
5.82 in​
16​
0.87​
5.86 in​
17​
0.87​
5.90 in​
18​
0.88​
5.94 in​
19​
0.88​
5.97 in​
20​
0.89​
6.00 in​
21​
0.89​
6.02 in​
22​
0.90​
6.05 in​
23​
0.90​
6.07 in​
24​
0.90​
6.09 in​
25​
0.90​
6.11 in​
26​
0.91​
6.13 in​
27​
0.91​
6.14 in​
28​
0.91​
6.16 in​
29​
0.91​
6.17 in​
30​
0.92​
6.19 in​

As another practical aside, having established the above, it wouldn't hurt to take some shots from your usual field positions at 100-yards, just to be sure you were right about your 4" circle hold ability in the first place. ;)
 

·
Registered
Joined
·
4,859 Posts
Back in 1984 as a young man interested in mathematical probabilities I met an older gentleman who taught trigonometry at the local community college, he was very interesting guy who had been a B29 pilot in WW2 but also loved shooting and hunting.
He worked up graphs and probability charts just like Uncle Nick, loved it.
What I took away from the mathematical probability charts is do the absolute best at the things you can control, accuracy of the gun and the shootability of it because the things you can't control can seriously degrade your ability to make good shots.
 

·
Super Moderator
Joined
·
13,751 Posts
True. I can't control a hurricane, but I can control my waste of ammunition by not trying to shoot in one.
 
  • Like
Reactions: Darkker

·
The Hog Whisperer (Administrator)
Joined
·
37,408 Posts
Not to mention changes in point of impact due to shooting from field positions, vs. sandbags on the bench. With some guns it doesn't matter.... with some it can really surprise you.
 

·
Registered
Joined
·
259 Posts
Discussion Starter · #93 ·
Interesting discussion for certain. This has answered a few of my questions and put others into perspective.

When I started this I did not really understand what the numbers meant other than the ES. That is the easy one. One of the largest question on that, that I had was what was causing this extreme differential I kept seeing. I didn't really care what the speed was, only was it relatively consistent. Which it wasn't.

Took a bit of work and experimentation to finally narrow it down to the brass I was using and the way I was processing it.
In the article linked there is a Table. 4.1 which breaks down loads by SD.. As mentioned here in my responses I would be OK with a 20 SD and 15 -10 would be outstanding. As I am fully aware that the components I am using certainly are Not Match grade. and there are plenty of practices and tool that I could be using to improve, but all of this has served to educate me more than any chit chat on a forum could.

I am finding that as my shooting and targets improve so has the quality of the components I am buying. Also slowly upgrading some of my reloading tools with many more to come as I progress. Yes I am letting my education on this continue!
 

·
Registered
Joined
·
18 Posts
The reason it is only used to gather speed numbers and not accuracy.
Which determines which load is likely to be more consistent (SD) and when you match those three you have your load. If you only using the chrono for speed numbers you are not using it's full potential
 

·
Registered
Joined
·
259 Posts
Discussion Starter · #95 ·
Which determines which load is likely to be more consistent (SD) and when you match those three you have your load. If you only using the chrono for speed numbers you are not using it's full potential
If you would have included the whole statement it would be obvious that this comment was in reference to using a Magneto Speed hung off the end of a barrel... Kind of hard to get true accuracy readings when there is something hanging from the barrel messing with the barrel harmonics now isn't it?
 

·
Registered
Joined
·
18 Posts
If you would have included the whole statement it would be obvious that this comment was in reference to using a Magneto Speed hung off the end of a barrel... Kind of hard to get true accuracy readings when there is something hanging from the barrel messing with the barrel harmonics now isn't it?
Actually yes, there's not much difference with it on or off unless it's a pencil barrel. Yes I have a Magnetospeed and a Caldwell. The Magnetospeed is more accurate and consistent. Point of impact can shift but the accuracy of the load is evident. If you know how to read your results.
 

·
Registered
Joined
·
259 Posts
Discussion Starter · #97 ·
Actually yes, there's not much difference with it on or off unless it's a pencil barrel. Yes I have a Magnetospeed and a Caldwell. The Magnetospeed is more accurate and consistent. Point of impact can shift but the accuracy of the load is evident.
Then I guess we will have to leave it at that as my results do not match yours. For certain POI changes and changes differently between 100/200/300yds when compared to it not being on the bareel. Also I have seen loads that actual group size has improved with it on and then fall apart once it has been removed.

So then please do explain how you read your results with it on.. Next are you shooting 6" targets @ 200yards or 1" targets at 200yds? Our rifle league is shooting the latter.
 

·
Super Moderator
Joined
·
13,751 Posts
Generally speaking, there are two ways to get cartridges tuned to hit the same point of impact. One is to get the velocity and barrel time absolutely consistent. Not easy. The other is to get barrel time synchronized to muzzle deflection (commonly called "vibration") so that it compensates for lower velocity by having the angle of departure slightly higher when they exit, and vice versa. The latter has the limitation that it will be best at just one range, where the slower and faster rounds have their trajectories cross one another. You can simulate the effect of this using an exterior ballistics program. You set the zero range to match the range at which the barrel vibration is tuned, then try calculating the trajectory for different velocities at the extremes of your usual extreme spread and see how the points of impact for the different velocities differ at all ranges that interest you that are not the zero (tuned) range.
 
  • Like
Reactions: KMW1954
81 - 99 of 99 Posts
Top