Can someone explain to me how people are measuring their groups? I've read some posts on here that say they are shooting .300 WM groups of .150" or so. That's smaller than the bullet.
Ben
Ben
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Groups smaller than bullet diameter?
- Thread starter Blhay7
- Start date
Bullet holes in paper are generally smaller than the bullet diameter. Measuring outside to outside and subtracting the bullet diameter will make the group spread appear smaller than it really is. It's generally a small discrepancy, so it may or may not matter depending on what you're doing.
In any event, the easiest way to accurately measure groups (and get other possibly useful info) is to use On Target software. Ver. 1.10 is freeware (link below). Simply scan or photograph a target, and save the file as a jpeg. If photographing, make sure the target is perfectly perpendicular with regard to the camera sight axis so the group image not distorted. Open the jpg file with On Target under "Open Image". You can then zoom in/out as needed to better see what you're doing. Click the button that has a line with an "x" at each end. Place the pointer at the edge of a target circle (or some other large object within the image that you can accurately measure), stretch it across keeping the line perfectly straight, then click the 2nd "X" on the other side. Enter the known measurement for that distance into the window that will appear. You have now calibrated the software for that image.
Next, select the correct caliber and distance at the right. Then click the "target button with a single bullet hole" above the image. When you click it, a circle with the approximate size of your caliber bullet holes will appear. You can now move the circle around. Center it over a bullet hole and click again. Repeat until all bullet holes in the group are accounted for. The group spread and other dimensional info will appear in tabular form at the right. To enter a new target within the same image, click "New Target" at right and repeat. The software will give you dimensional info for each target you enter, but it will also give statistical analysis for all the targets entered within a single image. It's very fast and easy, and much more reliable than trying to measure with calipers. Obviously, for many it may not be necessary to determine group spreads to this level of precision, but it's so simple and quick there's little reason not to use it. Once finished, you can print the target image and group spread data in your datebook if desired.
On Target Download
In any event, the easiest way to accurately measure groups (and get other possibly useful info) is to use On Target software. Ver. 1.10 is freeware (link below). Simply scan or photograph a target, and save the file as a jpeg. If photographing, make sure the target is perfectly perpendicular with regard to the camera sight axis so the group image not distorted. Open the jpg file with On Target under "Open Image". You can then zoom in/out as needed to better see what you're doing. Click the button that has a line with an "x" at each end. Place the pointer at the edge of a target circle (or some other large object within the image that you can accurately measure), stretch it across keeping the line perfectly straight, then click the 2nd "X" on the other side. Enter the known measurement for that distance into the window that will appear. You have now calibrated the software for that image.
Next, select the correct caliber and distance at the right. Then click the "target button with a single bullet hole" above the image. When you click it, a circle with the approximate size of your caliber bullet holes will appear. You can now move the circle around. Center it over a bullet hole and click again. Repeat until all bullet holes in the group are accounted for. The group spread and other dimensional info will appear in tabular form at the right. To enter a new target within the same image, click "New Target" at right and repeat. The software will give you dimensional info for each target you enter, but it will also give statistical analysis for all the targets entered within a single image. It's very fast and easy, and much more reliable than trying to measure with calipers. Obviously, for many it may not be necessary to determine group spreads to this level of precision, but it's so simple and quick there's little reason not to use it. Once finished, you can print the target image and group spread data in your datebook if desired.
On Target Download
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Center to center. This allows group size to be measured on the merits of accuracy alone, without giving weight to caliber.
All bullets in EXACTLY the same hole would be 0.
All bullets in EXACTLY the same hole would be 0.
Measuring groups is an indication of repeatability, not accuracy. If you put all the shots of a group in one hole, your rifle is repeatable. If you put all your rounds in one hole and the hole is in the dead center of the bull, then the rifle is repeatable and accurate. If you put all the rounds in one hole but the hole is 1" right and 2" high of the bull, then it is repeatable but not accurate. Accuracy is a relationship of point of aim = point of impact; repeatability is a relationship of the juxtaposition of the point of impact of all the rounds of a group.
I understand your point, but by that definition, wouldn't a rifle that shoots a 10 MOA group, but PERFECTLY centered around the POA, be considered "accurate"? I would consider it "perfectly-sighted," but definitely not accurate.
The specific group dimensions for what is considered "accurate" or "precise" can vary widely depending on the individual and what they're trying to accomplish. For some, 1 MOA is sufficient. Others might not be satisfied unless they're getting sub-quarter minute groups. It all depends. Using a quality optic, accuracy to some extent matters less than precision because if you're getting good precision, you can always dial it in such that POA = POI. With even a halfway decent modern firearm, I don't think anyone would consider 10 MOA to be either "accurate" or "precise".
You aren't understanding what group size is. It's a measurement of center to center of bullet impacts. Has nothing to do with the size of the bullet. Yes a .3MOA group at 100 yards with a .50 will make a bigger hole than a .3 MOA group at 100 yards with a .223. But the distance between where the bullets impacted is still .3MOA. Otherwise we wouldn't really be measuring accuracy.
The specific group dimensions for what is considered "accurate" or "precise" can vary widely depending on the individual and what they're trying to accomplish. For some, 1 MOA is sufficient. Others might not be satisfied unless they're getting sub-quarter minute groups. It all depends. Using a quality optic, accuracy to some extent matters less than precision because if you're getting good precision, you can always dial it in such that POA = POI. With even a halfway decent modern firearm, I don't think anyone would consider 10 MOA to be either "accurate" or "precise".
First, just to be candid, I'm just having a little fun with the semantics, not making a serious argument, so please take the following in that light...
I don't disagree with the points being made in either Killer Spade's post, or yours. I think I prefer the term you used - "precise," over "repeatable," simply because it seems more descriptive to say, "This is a very precise rifle," than it does to say, "This is a very repeatable rifle," but they really mean the same thing. However, to get really picky, by the above definitions of "accuracy," NO "rifle" can possibly be accurate, because by this definition accuracy is dependent upon the interaction between the rifle itself, and the sights. In other words, only the "system" (rifle + sights) can be accurate, and "accuracy" (unlike "precision") cannot be an inherent trait of the rifle itself. But then your other point brings things more together - that really only "precision" matters, because we all know that with a quality optic and mounting system, we can make ANY "precise" rifle DEADLY "accurate" in just three shots, given a suitable target at a known distance. That was kind of my point about the 10 MOA rifle. It could be made perfectly "accurate" by the proposed definition, but it sure wouldn't be useful for very much. It was kind of a way of suggesting that from a practical-use standpoint, the term 'accuracy" really should sort of imply that "precision" is part of the deal, if we are describing a rifle (system?) as "accurate."
Anyway, as I said, semantics that really don't amount to much.
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All this talk of semantics and that and you guys forgot the least precise component of the system, namely, the shooter.
Well, not really. There's no doubt you are right about the shooter, but I think for the purposes of the discussion, we were all taking him out of the equation so we can talk purely about the capabilities of the equipment only. You put the shooter in the equation and nobody can figure out what's going on!
As stated groups are measured center to center. If the group is not in one hole measure from the inside edge to the outside edge of the widest shots so if the holes in the target are undersize you still get a true reading. If all in one hole various methods are used for scoring in competition.
Some military standards use outside-to-outside, in which case a one hole group would be the diameter of the bullet. In the real world we use center-to-center, as it more realistically tells the true amount of dispersion.
One thing for sure, a grouping is synonymous with shot misplacement, that's to say, shots going somewhere other than where aimed. If shots all went where aimed the literal definition of a zero would be realized, where point of impact and line of sight intersect and the resulting value in any form of measurement is zero.
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When you get bored shooting groups, start going for the longest most accurate CBS you can make.
Far far more challenging. Obviously takes good groups to GET there but after watching benchrest shooters, I lost interest in group s ize.
But the CBS, that makes a good challenge on both shooter and equipment.
I've had a 1" at 600, (and I 've had a 3" at 600).
Best at 1k was about 12" though
I like to think luck played a huge part of that.
Far far more challenging. Obviously takes good groups to GET there but after watching benchrest shooters, I lost interest in group s ize.
But the CBS, that makes a good challenge on both shooter and equipment.
I've had a 1" at 600, (and I 've had a 3" at 600).
Best at 1k was about 12" though
I like to think luck played a huge part of that.Gstaylorg:
If I can get a little group, I can always adjust the scope and move the group.
Look at a benchrest target. There is a big black box on top and a circle for a center. That circle is called the mothball. Most shooters put the vertical crosshair on one side of the mothball and the horizontal crosshair on the bottom of the mothball. The group is typically somewhere else on the target -- it doesn't matter where. The group is almost never in the mothball. If you shoot at the mothball, any impact that hit the line would shoot out your aimpoint. The best (or most lucky) shooters can squeeze a group inside the mothball but why bother? One "failure to read the conditions" and you lose an aiming edge. FWIW, I have no idea where the big black box came from. I have never seen anyone shoot at it on purpose.
These days, I shoot steel and if I can hit the damn thing I am pretty happy. Regardless of hold or dial I try to keep them in the center but consistently hitting the 12-inch plate at 900 with my 308 is pretty tough for me.
Group measurement. The group size is the smallest circle that contains all of the bullet centers. Measure the distance between the bullet holes that are farthest apart in the group. For example suppose you have five bullets on the target with 4 in a knot and 1 hole an inch high, measure from the bottom the knot to the top of the upper hole. Use a dial caliper. Suppose that measurement is 1.308. Subtract bullet diameter 1.308 - .308 = 1.000. Behold a 1 inch group. Sometimes the bullets are more spread out and you have to try two or three different measurements.
If I can get a little group, I can always adjust the scope and move the group.
Look at a benchrest target. There is a big black box on top and a circle for a center. That circle is called the mothball. Most shooters put the vertical crosshair on one side of the mothball and the horizontal crosshair on the bottom of the mothball. The group is typically somewhere else on the target -- it doesn't matter where. The group is almost never in the mothball. If you shoot at the mothball, any impact that hit the line would shoot out your aimpoint. The best (or most lucky) shooters can squeeze a group inside the mothball but why bother? One "failure to read the conditions" and you lose an aiming edge. FWIW, I have no idea where the big black box came from. I have never seen anyone shoot at it on purpose.
These days, I shoot steel and if I can hit the damn thing I am pretty happy. Regardless of hold or dial I try to keep them in the center but consistently hitting the 12-inch plate at 900 with my 308 is pretty tough for me.
Group measurement. The group size is the smallest circle that contains all of the bullet centers. Measure the distance between the bullet holes that are farthest apart in the group. For example suppose you have five bullets on the target with 4 in a knot and 1 hole an inch high, measure from the bottom the knot to the top of the upper hole. Use a dial caliper. Suppose that measurement is 1.308. Subtract bullet diameter 1.308 - .308 = 1.000. Behold a 1 inch group. Sometimes the bullets are more spread out and you have to try two or three different measurements.
When you get bored shooting groups, start going for the longest most accurate CBS you can make.
Far far more challenging. Obviously takes good groups to GET there but after watching benchrest shooters, I lost interest in group s ize.
But the CBS, that makes a good challenge on both shooter and equipment.
I've had a 1" at 600, (and I 've had a 3" at 600).
Best at 1k was about 12" though
I have seen some pretty awesome groups on a benchrest range (quite a few groups less than a 0.1 inch at 100 yards) but this is my personal "most lucky group". That is a 5-shot .536 MOA group at 1,000 yards. Perfect conditions - that is, no conditions. Five quick rounds. Starting from cold bore. I have shot several other 0.9 moa groups but nothing like that. That is not skill, it is just luck.
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LOL! I'm almost certain that "big black box" is supposed to be the aim point. You center your crosshairs in it ("quartering" it), and what you are calling a "mothball" is the target. You would click down five clicks to use it at 100 yards (quarter moa clicks). I might be wrong, but that's how I understand it.
Inserted an image so we all know what we are talking about.
You must be right. I was very active in BR in the 90s; the first day I shot a BR rifle I was told to use the mothball as my aim point. During that time I never spoke with anyone who used the big box for their aim point.
I just checked a target. As you said, the center of the big box is 5 clicks up from the center of the mothball. The concentric circles are 1/4-inch apart. The lines in the concentric circles are 0.062 wide (1/8 inch) and the mothball circle is 0.083 wide. The inside of the mothball is about 0.375, the outside is about 0.525. The outside of the big box is 1 inch, the inside white box is 1/2 inch. Using fine cross hairs, I can hold more closely to the same aim point using the edges of the mothball than quartering the big box or using its edges. I find that trying to hold on the box edges, the black cross hairs get lost in the black box. YMMV.
For comparison, if a 6PPC group fit inside the mothball, it would be .375-.243 = .132. That is a very good group but not fantastic (unless the wind was blowing). If it was a 22, then the measurement would be 0.375 - 0.223 = 0.152 - really good, not fantastic (unless the wind was blowing). I personally shot very few groups in the ones. If you shot for the inside of the mothball and had one slip a little, the edge of the hole would be in the black circle and that makes it tough for the guy measuring the target to get the measurement right. Making it hard for the target measuring guy is not the best way to get a good score so -- we shoot away from the mothball.
Thanks for that info!
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It is my opinion that BR shooters have to master the equipment while prone shooters have to master their body.
(No disrespect is intended here, that is still impressive!) But my question there is, how far is your CBS from the cold bore AIM POINT?
I cannot tell how big that steel is, looks like it could be 3-4' across, meaning you could be 12-18" off target.
I bet it would be harder to shoot a CBS dead center on that target than to shoot that group (??).
One of the most challenging groups I ever shot was a 22 rimfire at 400 yards. That's not easy and it's a test of machine and master.
BR has it's place but for me, personally, rather boring. Lock a rifle down and see if it can repeat itself.
A few years ago someone here to ok a 6.5 swede mauser and started shooting for 1000 yards, and made it. Underdog using a 60 or 70 year old rifle - that's challenging!
If I could see someone do groups like that with a K98 or an antique - that would impress me!
I guess I'm getting old(er), Next thing you know I'll be using a c-sharpes at 1000.......hmmm that's not a bad idea...
The plate is 36 inches in diameter - 1 mil in the scope. On that day my aim point was the center of the plate, about a foot to the left - about 1.25 MOA or .3 mills. I think that the group ended up there because on that day I did not adjust for spin drift. With those bullets at that range, spin drift is just a hair over 1 MOA.
I still have the BR shooter attitude -- I can always adjust the scope to move the group. I never shot bullseye so my score and place came from group size, not distance from the center.
Today, at 1,000 yards, my groups average 1 MOA +- 0.1 MOA. At my skill level, I need fairly good conditions to do that. If I can consistently make A-zone hits at 1,000 yards with tougher conditions, then I will have the skill I want. At that shooting range there is a 12-inch plate and an IPSC target at 1,000 yards. When I can hit the IPSC target in most conditions and hit the 12-inch steel about 8 out of 10 times, I will be pretty happy. When I can do that with my 308 I will be overjoyed. You have your standards and goals, I have mine.
I still have the BR shooter attitude -- I can always adjust the scope to move the group. I never shot bullseye so my score and place came from group size, not distance from the center.
Today, at 1,000 yards, my groups average 1 MOA +- 0.1 MOA. At my skill level, I need fairly good conditions to do that. If I can consistently make A-zone hits at 1,000 yards with tougher conditions, then I will have the skill I want. At that shooting range there is a 12-inch plate and an IPSC target at 1,000 yards. When I can hit the IPSC target in most conditions and hit the 12-inch steel about 8 out of 10 times, I will be pretty happy. When I can do that with my 308 I will be overjoyed. You have your standards and goals, I have mine.
That is what I enjoy about this sport. We're all at different skill levels, different equipment, etc...
I have 2 standards for myself. My first standard is "will it put dinner on the table" covering POA, The 2nd standard is if I were a Boy Scout, would it earn me my rifle merit badge? (5, 5 shot groups within the diameter of a quarter). Those are probably pretty weak standards for a lot of guys but since I'm a LR newbie, you gotta start somewhere that is attainable.
