Acceptable group size?

Good post Joe.

But I will say that shooting a 250-25x on a USBR target at 50yds and actually doing with witnesses ain't going to happen in our lifetime at least not unless a miracle happens and God helps steer each bullet. :D

As far as score shooting goes, shooting the highest possible points on score targets and not counting any x's, the 2500 ARA target is way tougher than just shooting a 250 IR50/50, RBA, or USBR target. ARA don't count x's anyways to my knowledge. A 2500 score more than likely is going to score a 250-25x on most targets if you score it as such. A 250-25x IR50/50 or RBA target is going to probably score a 2500 ARA target.

But for shooting perfect scores goes, the USBR target is by far the toughest to do if your talking about a 250-25x score.

Brad
 
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shoot for score

Statisticaly speaking, average raduis from group center would best aproximate actual br target scores. problem is it is imposible to do this even from a 3-shot group (if it is a br class rifle;)). Back to the question---- why not shoot for score:confused:? there are br50 practice targets that you can downlaod from the web. if you dont want to shoot 25 rounds, shoot 5 rounds and multiply score by 5 including the x's:D.
 
Yup:

If you don't count Xs, the ARA target is the toughest.
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AllXtargets.jpg

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But: If you wanted to count the dot on the ARA target as an X: And you shot it completely out, as you must shoot out the 10 ring on the USBR, the group size would still not be as demanding as the group needed for a 25x on the USBR.

Not sure of the dot size on the ARA target, but if it is the same size as the dot on the IR-50/50, the group size needed to get a 2500-25x would be .224 - .032 = .192"


So: Another way to look at it is: If we had an X count on all three targets:
The needed 25 shot group sizes would be:
USBR .124"
ARA .192"
IR-50/50 .256"

I believe to get an X on the IR-50/50 target the shot must just touch the dot, not punch it out: Right?
 
Your correct Joe.

I was just stating that no one to my knowledge has ever even come close to shooting a 50yd 250-25x USBR target. A 250-10x would be a smokin.
 
Brad
Best you check out some of the records......There are some 250s with 20 plus Xs.
Fred K
 
Thanks for all the replies, when I can get out I will take some pictures of my groups and my gun and get your guys/gals expert opinion, I would really like to know what everybody thinks.
Thanks
Bored184
 
Fred,

I'm familiar with all the records that have been shot. I've pretty well got them in the back of my head who shot what and who holds all the records. What I was saying is to the best of my knowledge no one has ever shot a 250-25x USBR target. It will be years before someone ever does. Shooting a 250-25x on a IR50/50 or RBA target is still not even close to shooting a 250-25x USBR target where you have to shoot out the entire 10 ring which is only .100 in diameter. You can't be off much with your bullet and it has to be almost perfectly centered or your not going to get an X. Shooting an x on the IR50/50 or RBA is not easy to do either, but a bullet that touches the inside edge on the dot isn't going to be close to an x on the USBR target.

If my math is correct, and you use a .224 plug, you can be off center of the 10 ring by about .060 either up, down, right, left or diagonally in between all of these with each bullet and still probably plug a 10x. Doing that on every single bull is dang near impossible. That's why I said God would have to be helping steer each bullet for the shooter to pull off a 250-25x USBR score at 50yds.

Brad
 
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I came up with the .060 being off center of the 10 ring on each target by taking the .100 for the diameter of each 10 ring and you have .124 left approx. That leaves about .062 you can be off center since you have to double that figure in order to shoot out each and every 10 ring with each bullet.

Brad
 
That's providing if you use the plug which actually will help your score on the shots that are borderline and don't really take out the entire 10 ring. The plug has been said to be your friend.

Brad
 
A plug will actually hurt your score shooting and ARA target. I've shot ARA targets that I could plainly see scored 100 on the actual target. But since they are borderline shots and close to breaking the 100 ring edge they stick a plug in the bullet hole and score it a 50. It's kind of weird in my mind how this whole plug thing works to be honest with the .224 diameter plugs that they use, but I guess it's fair for all since they should be plugging borderline shots for all shooters. But technically speaking, a 22 bullet won't print a .224 diameter hole. I've seen other targets that other shooters have shot that scored 100 on the paper no doubt about it, but were plugged and given a 50 score as well. Technically it's fair to all, but in reality shooters or being ripped off from what the bullet actually truely scored on ARA targets.

That's the truth. Not complaining, but it is reality.

Brad
 
Brad, a plug does not help or hurt. The rimfire bullet is nominally .224 in diameter. Yes, the hole "appears" to be smaller because of the paper rebound but the bullet went through it so the hole can't be smaller. I have scored a lot of position targets both rimfire and highpower in my life and plugged a lot of holes and I have yet to hear anyone complain that the plug helped.

BTW, are benchrest targets scored with a light box behind the target?
 
I understand what your saying but technically speaking your wrong. When you shoot a group with your 22 rifle, and measure it from farthest outside smear to smear or lead ring or powder smear or whatever you want to call it, the bullets that made up the group never really on avg print a .224 hole. But yet most and a lot of guys will deduct .224 for bullet diameter. So technically speaking if our rimfire bullets although they are .224 in true diameter going to our targets, and they only print a .204 bullet hole avg, then why are we using .224 for bullet diameter to subtract from outside to outside edge? The same can be said for why we are using a .224 plug to plug our holes when on paper the bullet prints a smaller hole. Why not just use a .204 plug?

And a plug can hurt your score shooting ARA targets. I've seen a target Joe Besche shot that scored a 100 but was plugged a 50 score. Why not just go by what the print of the bullet is saying and be done with it and use a smaller plug?

Brad
 
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Brad,
Using your method, I wonder how many different size plugs the judges would need to score each shooters targets. Not all ammo cuts the same size hole. :confused:

Every target is scored with the same plug (.224), that is the only fair way to do it. And that is what the rules call for. If the rules were changed now to use your method, what happens to all the targets that were scored in the past at less then 2500 because of close 50s? Do we throw out all the records and start over?
Jerry
 
Jerry,

I'm not saying to change anything just proving my point that the print of bullets on paper get scored according to the plug that is .224 in diameter. My whole point was to say that when use the scenario of groups to illustrate the point that measuring outside edge to edge we don't add on to the diameter of what that measurement is for the supposedly true diameter, but yet we use a plug to in fact do that when we score shoot. I see the need to have a norm or standard to go by, but just illustrating my point.

Brad
 
The way I see it . . .

I have measured a number of bullet holes from edge to edge of the lead/grease smear. I found the range to be from about .214" to .219". The variation is the result of:
1. Paper thickness.
2. Length of fibers.
3. Moisture content.
4. Diameter and shape of bullet.
5. Type of lubricant on the bullet.
6. Angle of bullet as it passes through the target.

And: Not all .22 rimfire bullets are of the same diameter. Lapua Midas L is .2240" and Midas M is .2232". AND: The grove diameter of the bore in some rimfire rifles is smaller than the bullet diameter.

Because of these variables, the best way to measure group size is with the Sweeny Reticule Rule as used by NBRSA, IBS and ARG in group tournaments: More accurate than measuring outside edge to outside edge and subtracting the diameter of a bullet, based on the lead/grease marks.

To use the reticule rule you first draw a line parallel to the length of the group. You close the caliper and, look through a magnifying glass, at a circular reticule of the correct size: (There are 3 or 4 different size reticules etched in the clear plastic plate). You center the .22 caliber reticule over the left hand bullet hole and check to be sure the caliper is parallel to the line your drew parallel to the length of the group.

With the round reticule centered over that left hand hole, you press done on a push pin that is built into the caliper, to anchor the rule to the paper. Then with a friction wheel on some models, or a small handle on others, you slide the caliper right until the reticule is centered over the hole on the right side of the group. Then you read the group size to the nearest thousandth of an inch on the caliper.

The Sweeny Reticle Rule can be attached to most dial or digital calipers and can be ordered from:
Robert Hart: 1 (800) 368-3656
or
Neil Jones: 1 (814) 763-2769

JonesReticuleRule-1.jpg
 
Brad, I understand the reason for using a different bullet diameter when measuring a group with a regular caliper. BUT, when you are measuring a position target or an ARA target the correct way is to use a .224 plug. The idea that that hurts scoring is wishful thinking. Besides, it doesn't matter what diameter the bullet is, by the time it reaches the target, it will be the diameter of the barrel. And what is the bore diameter of most barrels? Or as Joe said, how many plugs would the scorer need?

And, ask Joe what the diameter of the reticle is on his caliper. .224 maybe?
 
My hole point is that what a bullet prints on paper, it ought to be scored by the print. When you print a sentence, it says what you printed. I'm not suggesting change, but really it is being done all wrong. We can argue all we want, it is what it is.

Joe,

I know you have measured a lot of bullet holes and targets as well. From the bullet holes I have measured, I have found .204 to be just about the normal avg for a bullet hole on the various types of paper used. I've measured 22 bullet holes down to .193 depending on the paper used like you said. I've seen very, very few that would calibrate to even .214. A lot can be seen under a magnifier and a super bright LED flashlight. That's according to my eyes. I have 20/13 vision.

Brad
 
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Well, just typing out loud here so....

Why not just use the bore dia of barrel .221/.222 for the plug? Seems to me that most bores would fall into this realm and unless I'm mistaken it's what the bullet dia. really is before it crashed headlong into that piece of paper.

Roger
 
Here's a couple of examples of bullet holes on USBR paper targets. ARA, IR50/50, and RBA targets will print more of a cleaner cut hole from my experiences. The diameter won't change that much though. These are some groups with fliers that I had sitting around. Like I said, you will get some to go up to around .210 if you have the eyes to measure them. I did these over a few times to be sure. The one on the left looks to be a smaller hole, but from smear to smear it isn't.

IMGP3782.JPG
 
HuskerP7M8 said:
Okay, if the above is true, we have one more problem.
No one is going to be willing to shoot 25 shot groups for determination of firearm accuracy or ammo testing.
I hope everyone is aware of the nature of group enlargement with the addition of each shot. I think we all know 2 shot groups will be smaller that 3 shot groups, 3 shots smaller than 5 shots, 5 shots smaller than 10 shots, etc.

Without doing a detailed statistical analysis for the group growth of 5 vs 25 shots, I’ll just make an educated guess which could be wrong and estimate that size as being somewhere in the low .2’s.

I have to go to work, so maybe someone else can jump in with a closer number.
Does this make sense to anybody or have I made any obvious errors?
Click to expand...

HuskerP7M8,

Not too long ago I did a calculation that can be used to address the question of how group size (extreme spread) depends on the number of shots in the group. I'm not a competition shooter, but I read this forum sometimes because I'm interested in the application of statistics and probability to shooting. So, when I saw your comment I thought maybe I could contribute something useful, which also has some connection to Bored184's question.

There are a couple of complications so bear with me. First the situation is complicated by the fact that the most common way to measure group size is extreme spread, ES (the distance between the two most widely separated holes). This is fine for scoring targets, but if you want to say anything about expected (that is, predicted) average group size for a shooter and/or equipment, it is a very poor statistic to use. For one thing as you pointed out it varies with the number of shots, and for another, just the natural random differences between groups will cause it (extreme spread aka group size) to vary substantially between groups even if they are effectively shot under identical conditions.

So, to see how group size varies you need something more constant to compare it against. There is a statistic which for the sake of discussion I'll call the "true group size" or TGS, which is completely independent of the number of shots in the group and so is a good description of average group size produced by a particular combination of shooter, rifle, load, etc. Rather than get into the details of that statistic here, I'll just say it exists and can be calculated.

Given all of this, the question of how group size/ES grows with increasing number of shots has to be answered in probabilities. I have a web page that lets people do the extreme spread (group size) probability calculation for different numbers of shots in a group and below I've listed probabilities of getting a group size (ES) greater than the "true group size" TGS, for 5, 10, and 25 shot groups. Remember, TGS (true group size) is a fixed size, independent of the number of shots in the group, ES will vary from group to group.

5 shot group
94.4% chance that ES > TGS
36.4% chance that ES > 1.5 x TGS
3.84% chance that ES > 2 x TGS

10 shot group
more than 99.99% chance that ES > TGS
86.9% chance that ES > 1.5 x TGS
16.2% chance that ES > 2 x TGS

25 shot group
more than 99.99% chance that ES > TGS
more than 99.99% chance that ES > 1.5 x TGS
64.1% chance that ES > 2 x TGS

So this tells you that for a 25 shot group the chance of seeing a group size more than twice as big as the TGS is 61.1/3.84 or about 16 times the chance of seeing that group size for a 5 shot group.

Keep in mind that if the conditions (barrel cleanliness, temp., etc.) are effectively the same, then five 5-shot groups are equivalent to one 25-shot group. This tells you a lot about "flyers".

I've left out some details and could fill them in if anyone is interested.
 
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